Updated on 2024/12/26

Information

 

写真a

 
SHIOTA YOSHIHITO
 
Organization
Institute for Materials Chemistry and Engineering Department of Fundamental Organic Chemistry Associate Professor
Graduate School of Engineering (Concurrent)
Title
Associate Professor
Contact information
メールアドレス
Tel
0928022530
Profile
学部、大学院における研究教育活動として、コンピュータを使った化学反応の理論解析を行っている。これまでに金属酸化物イオンにより触媒されるメタンーメタノール転化反応を理論的に解析し、反応性、反応メカニズムを明らかにした。 さらにC-H結合を活性化する遷移金属の触媒作用を理論計算により明らかにするとともに、触媒や酵素のモデルを用いて触媒反応の解析をおこなった。

Research Areas

  • Nanotechnology/Materials / Bio chemistry

  • Nanotechnology/Materials / Inorganic/coordination chemistry

  • Natural Science / Mathematical physics and fundamental theory of condensed matter physics

  • Nanotechnology/Materials / Fundamental physical chemistry

Degree

  • Doctor of Engineering

Research History

  • Kyushu University Institute for Materials Chemistry and Engineering Associate Professor 

    2014.7 - Present

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Research Interests・Research Keywords

  • Research theme: 基礎化学

    Keyword: 基礎化学

    Research period: 2024

  • Research theme: 反応機構

    Keyword: 反応機構

    Research period: 2024

  • Research theme: 原子価互変異性

    Keyword: 原子価互変異性

    Research period: 2024

  • Research theme: 分子力学

    Keyword: 分子力学

    Research period: 2024

  • Research theme: メタン活性化

    Keyword: メタン活性化

    Research period: 2024

  • Research theme: メタンモノオキシゲナーゼ

    Keyword: メタンモノオキシゲナーゼ

    Research period: 2024

  • Research theme: ミニマムクロッシングポイント

    Keyword: ミニマムクロッシングポイント

    Research period: 2024

  • Research theme: ヘムオキシゲナーゼ

    Keyword: ヘムオキシゲナーゼ

    Research period: 2024

  • Research theme: トラジェクトリ法

    Keyword: トラジェクトリ法

    Research period: 2024

  • Research theme: チロシナーゼ

    Keyword: チロシナーゼ

    Research period: 2024

  • Research theme: スピン軌道相互作用

    Keyword: スピン軌道相互作用

    Research period: 2024

  • Research theme: スピンクロスオーバー

    Keyword: スピンクロスオーバー

    Research period: 2024

  • Research theme: シトクロムP450

    Keyword: シトクロムP450

    Research period: 2024

  • Research theme: コバルト錯体

    Keyword: コバルト錯体

    Research period: 2024

  • Research theme: transtion state

    Keyword: transtion state

    Research period: 2024

  • Research theme: electronic structure

    Keyword: electronic structure

    Research period: 2024

  • Research theme: Dnsity functional theory

    Keyword: Dnsity functional theory

    Research period: 2024

  • Research theme: 密度汎関数法

    Keyword: 密度汎関数法

    Research period: 2024

  • Research theme: 電子輸送

    Keyword: 電子輸送

    Research period: 2024

  • Research theme: 電子状態

    Keyword: 電子状態

    Research period: 2024

  • Research theme: 鉄錯体

    Keyword: 鉄錯体

    Research period: 2024

  • Research theme: 金属錯体

    Keyword: 金属錯体

    Research period: 2024

  • Research theme: 金属酵素

    Keyword: 金属酵素

    Research period: 2024

  • Research theme: 量子化学計算

    Keyword: 量子化学計算

    Research period: 2024

  • Research theme: 量子化学

    Keyword: 量子化学

    Research period: 2024

  • Research theme: 酸素活性化

    Keyword: 酸素活性化

    Research period: 2024

  • Research theme: 酵素反応

    Keyword: 酵素反応

    Research period: 2024

  • Research theme: 酵素化学

    Keyword: 酵素化学

    Research period: 2024

  • Research theme: 遷移金属錯体

    Keyword: 遷移金属錯体

    Research period: 2024

  • Research theme: 遷移状態

    Keyword: 遷移状態

    Research period: 2024

  • Research theme: 触媒反応

    Keyword: 触媒反応

    Research period: 2024

  • Research theme: 触媒化学

    Keyword: 触媒化学

    Research period: 2024

  • Research theme: 生物無機化学

    Keyword: 生物無機化学

    Research period: 2024

  • Research theme: 理論計算

    Keyword: 理論計算

    Research period: 2024

  • Research theme: 理論化学

    Keyword: 理論化学

    Research period: 2024

  • Research theme: 無機化学

    Keyword: 無機化学

    Research period: 2024

  • Research theme: 密度汎関数理論

    Keyword: 密度汎関数理論

    Research period: 2024

  • Research theme: Theoretical study of C-H bond activation by metal-oxo species Theoretical study of oxygen activation by metalioenzyme Theoretical study of thermal reaction of organic silicon compounds Theoretical study of zeolite catalyst Large scale calculation of enzymatic reaction Theoretical study of Spin-crossover phenomenon

    Keyword: theoretical chemistry computational chemistry

    Research period: 2001.5 - 2010.3

Papers

  • Dynamic Luminescence Vapochromism of Pyridinium‐Based Organic Salts

    Verner Sääsk, Ayano Abe, Yohei Kametani, Yoshihito Shiota, Osamu Sato, Chihaya Adachi

    Chemistry – A European Journal   30 ( 69 )   e202402777   2024.12   ISSN:0947-6539 eISSN:1521-3765

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    Organic vapochromic materials which undergo a drastic change in their photophysical properties upon exposure to vapors or gases are attracting growing scientific attention because of their low price and wide range of possible applications. In this work, luminescence vapochromism of carbazole-pyridinium-based organic salts with a general structure of (CzPy)X (CzPy+=2,3-di(9H-carbazol-9-yl)pyridinium ion; X=Cl, Br or I) is reported. It was found that (CzPy)X compounds form J-aggregates, which rearranged back to monomeric form upon exposure to methanol, ethanol, acetone, and water vapors. In contrast, acetonitrile was found to promote the J-aggregation in (CzPy)X compounds by occupying the voids in their crystal lattice and pushing cations closer together. It was further demonstrated that the efficiency of J-aggregation in (CzPy)X compounds depends on the size of the anion, which was employed to realize dynamic luminescence vapochromism, with vapochromic response times ranging from a couple of minutes in (CzPy)Cl to more than an hour in (CzPy)I. In addition, (CzPy)X compounds exhibited high melting points of about 250 °C and excellent thermal stability. (CzPy)Cl and (CzPy)Br have also shown good photoluminescence quantum yields at room temperature in a solid state.

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  • Mechanistic studies of NOx reduction reactions involving copper complexes: encouragement of DFT calculations

    Yohei Kametani, Yoshihito Shiota

    Dalton Transactions   53 ( 48 )   19081 - 19087   2024.12   ISSN:1477-9226 eISSN:1477-9234

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Dalton Transactions  

    The reduction of nitrogen oxides (NOx), which is mainly mediated by metalloenzymes and metal complexes, is a critical process in the nitrogen cycle and environmental remediation. This Frontier article highlights the importance of density functional theory (DFT) calculations to gain mechanistic insights into nitrite (NO2−) and nitric oxide (NO) reduction reactions facilitated by copper complexes by focusing on two key processes: the reduction of NO2− to NO by a monocopper complex, with special emphasis on the concerted proton-electron transfer, and the reduction of NO to N2O by a dicopper complex, which involves N-N bond formation, N2O2 isomerization, and N-O bond cleavage. These findings underscore the utility of DFT calculations in unraveling complicated reaction mechanisms and offer a foundation for future research aimed at improving the reactivity of transition metal complexes in NOx reduction reactions.

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  • Self‐Assembly of Thienopyrrole‐Fused Thiadiazoles Containing an Amide Linker: Control of Supramolecular Polymerization Mechanism and Chiroptical Properties by Trialkoxy Side Chains

    Taiki Yamaguchi, Yukako Naito, Chitoshi Kitamura, Hiroki Takeshita, Shohei Ida, Tsutomu Ishi‐i, Kazumasa Suzuki, Taisuke Matsumoto, Yoshihito Shiota, Daiya Suzuki, Yoshitane Imai, Toshiaki Ikeda, Shin‐ichiro Kato

    Chemistry – An Asian Journal   19 ( 23 )   e202400829   2024.12   ISSN:1861-4728 eISSN:1861-471X

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Chemistry - An Asian Journal  

    Three thienopyrrole-fused thiadiazole (TPT) fluorescent dyes featuring a common amide linker and different alkoxy substituents on peripheral trialkoxybenzene moieties were synthesized, and their self-assembly behavior in solution was investigated. The obtained results revealed a substantial steric effect of the alkoxy substituents on the supramolecular polymerization mechanism, which results from a combination of π-stacking and hydrogen (H)-bonding interactions. Detailed spectroscopic measurements revealed that with increasing steric demand of the substituents, the supramolecular polymerization processes in pure methylcyclohexane (MCH) or a mixture of MCH and toluene become temperature-sensitive and enthalpically favorable, resulting in a change from the isodesmic assembly mechanism to the cooperative mechanism. Theoretical calculations suggested that in TPTs with bulky substituents, steric hindrance causes the H-bonding array of the amide moieties to be aligned along the stacking axis of the π-systems; thus, the H-bonding interactions are strengthened compared to those in TPTs with less bulky substituents, compensating for the weakened π-stacking interactions. A chiral TPT derivative with (S) stereogenic centers was found to form homochiral helical supramolecular assemblies that generate discernible circularly polarized luminescence. Achiral TPTs also generate helical assemblies to which preferential helicity can be imparted through the external chiral bias of the solvents (R)- and (S)-limonene.

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  • Photocatalytic Substrate Oxidation Catalyzed by a Ruthenium(II) Complex with a Phenazine Moiety as the Active Site Using Dioxygen as a Terminal Oxidant

    Tomoya Ishizuka, Taichiro Nishi, Nanase Namura, Hiroaki Kotani, Yasuko Osakada, Mamoru Fujitsuka, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    Journal of the American Chemical Society   146 ( 48 )   33022 - 33034   2024.11   ISSN:0002-7863 eISSN:1520-5126

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    DOI: 10.1021/jacs.4c09962

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  • B12‐Catalyzed Carbonylation of Carbon Tetrahalides: Using a Broad Range of Visible Light to Access Diverse Carbonyl Compounds

    Keita Shichijo, Miho Tanaka, Yohei Kametani, Yoshihito Shiota, Mamoru Fujitsuka, Hisashi Shimakoshi

    Chemistry – A European Journal   e202403663   2024.11   ISSN:0947-6539 eISSN:1521-3765

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Chemistry - A European Journal  

    Visible-light-driven organic synthesis is a green and sustainable method for producing fine chemicals and is highly desirable at both laboratory and industrial scales. In this study, we developed a broad-range (including the red region) visible-light-driven carbonylation of CCl4, CBr4, and CBr3F with nucleophiles, such as amines and alcohols, using a B12−Mg2+/TiO2 hybrid catalyst. Carbonyl molecules such as ureas, carbamates, carbonate esters, and carbamoyl fluorides were synthesized with high selectivity and efficiency under mild conditions. Diffuse reflectance UV-vis spectroscopy, femtosecond time-resolved diffuse reflectance spectroscopy, and density functional theory calculations revealed the reaction mechanism is a combination of SN2 and single-electron transfer. This is a rare example of a low-energy, red-light-driven photocatalysis, which has been a highly desired organic reaction in recent years. We believe that this study provides a general platform to access diverse carbonyl molecules and could promote photocatalytic carbonylation reactions on a pilot scale.

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  • The Effect of Intramolecular Proton Transfer on the Mechanism of NO Reduction to N2O by a Copper Complex: A DFT Study

    Ryoga Toyoshima, Yohei Kametani, Kazunari Yoshizawa, Yoshihito Shiota

    Inorganic Chemistry   63 ( 46 )   22138 - 22148   2024.11   ISSN:00201669

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    DFT calculations were performed to explore the mechanism underlying the reduction of NO to N2O by a CuI complex. A nitrosyl complex reacts with another NO molecule and the CuI complex, leading to the formation of a dicopper-hyponitrite complex (Cu2N2O2). The first steps follow a common pathway until the formation of the intermediate [CuII-N2O2]+, after which the reaction pathway diverges into three Cu2N2O2 species: κ2-N,N′, κ2-O,O′, and κ3-N,O,O′. These species yield different products along their respective reaction pathways. In the case of the κ2-N,N′ and κ3-N,O,O′ species, the subsequent steps involve a methanol-mediated proton transfer and N-O bond cleavage, resulting in the generation of N2O and [CuII-OH]+. Conversely, for the κ2-O,O′ species, two proton transfers occur without N-O bond cleavage, leading to the formation of H2N2O2 and [CuII]2+. H2N2O2 spontaneously converts into N2O and H2O. These computational results elucidate how the coordination mode of hyponitrite influences reactivity and provide insights into NO reduction via proton transfer. Notably, switching of the N2O2 coordination mode to metal ions from N to O was not required, offering insights for more efficient NO reduction strategies in the future.

    DOI: 10.1021/acs.inorgchem.4c03619

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  • (PNCP)Ir vs (PNNP)Ir: Neutral Iridium Complex for Direct Hydrogenation of Carboxylic Acids

    Koichiro Nishimoto, Naoki Noto, Yohei Kametani, Bendik Gro̷mer, Chihaya Murata, Hiroko Okuwa, Yoshihito Shiota, Kazunari Yoshizawa, Susumu Saito

    Organometallics   43 ( 23 )   3013 - 3021   2024.10   ISSN:0276-7333 eISSN:1520-6041

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    Herein, we demonstrate the significant impact of tetradentate-ligand-coordinated metal complexes, which have not yet been exploited for the direct catalytic hydrogenation of carboxylic acids (CAs). Our previously developed cationic iridium complex coordinated with a PNNP-ligand [(PNNP)Ir] is effective for hydrogenating esters and carboxylic anhydrides generated in situ from CAs but unsuitable for the direct hydrogenation of CAs. In sharp contrast, the corresponding neutral iridium complex with a PNCP-ligand [(PNCP)Ir] developed in this study facilitates the direct hydrogenation of CAs, including biorelevant and pharmaceutical compounds, under not more than 1 MPa of H2. Quantum-chemical calculations indicated that (PNCP)Ir is kinetically a far more competent catalyst than (PNNP)Ir, particularly for the C-H bond formation via hydride transfer from Ir-H to the carbonyl carbon of CA, which was identified as the rate-determining step. While Ir-carboxylates are in resting states throughout the catalytic cycle, CA itself barely interacts with the Ir center during the hydride transfer process.

    DOI: 10.1021/acs.organomet.4c00355

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  • A Stealthiness Evaluation of Main Chain Carboxybetaine Polymer Modified into Liposome

    Najmina, M; Kobayashi, S; Shimazui, R; Takata, H; Shibata, M; Ishibashi, K; Kamizawa, H; Kishimura, A; Shiota, Y; Ida, D; Shimizu, T; Ishida, T; Katayama, Y; Tanaka, M; Mori, T

    PHARMACEUTICS   16 ( 10 )   2024.10   ISSN:1999-4923 eISSN:1999-4923

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  • Ferrocenyl PNNP Ligands-Controlled Chromium Complex-Catalyzed Photocatalytic Reduction of CO2 to Formic Acid

    Taku Wakabayashi, Yohei Kametani, Eimi Tanahashi, Yoshihito Shiota, Kazunari Yoshizawa, Jieun Jung, Susumu Saito

    Journal of the American Chemical Society   146 ( 38 )   25963 - 25975   2024.9   ISSN:0002-7863 eISSN:1520-5126

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    3d-transition metal complexes have been gaining much attention as promising candidates for photocatalytic carbon dioxide (CO2) reduction systems. In contrast to the group 7-12 elements, Cr in group 6 has not yet been investigated as the catalyst of CO2 photoreduction because of its intrinsic disadvantages. Cr has a weak reducing ability due to an insufficient number of d electrons and high Lewis acidity which may deactivate the catalyst by strong coordination with a product formate. To overcome these drawbacks, we rationally designed molecular Cr complexes bearing ferrocenyl PNNP tetradentate ligands (FcCrCy, FcCriPr, FcCrtBu, and FcCrPh). These Cr complexes selectively converted CO2 into formic acid (HCO2H) under photocatalytic conditions and, to our knowledge, represent the first molecular Cr catalysts for CO2 photoreduction. The best catalyst FcCrPh achieved a turnover number of 1180 for HCO2H formation with 86% selectivity after 48 h of light irradiation, with a combined use of an organic photosensitizer. Electrochemical and continuous UV-vis absorption analyses clarified the sequential reaction pathways involving multielectron reduction and protonation of a Cr complex. Moreover, through detailed computational studies, photoinduced electron transfer mediated by ferrocenyl groups and intramolecular proton transfer attributed to hemilabile phosphine ligands would be key to the efficient catalysis that overwhelms the inherent disadvantages of Cr.

    DOI: 10.1021/jacs.4c03683

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  • A new class of crystalline X-ray induced photochromic materials assembled from anion-directed folding of a flexible cation

    Hong Jin Liao, Zhu Zhuo, Qing Li, Yoshihito Shiota, Jonathan P. Hill, Katsuhiko Ariga, Zi Xiu Lu, Lu Yao Liu, Zi Ang Nan, Wei Wang, You Gui Huang

    Chinese Chemical Letters   35 ( 8 )   2024.8   ISSN:1001-8417 eISSN:1878-5964

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    Electron-deficient viologens are widely used as ligands or structure-directing agents (SDAs) to synthesize crystalline X-ray induced photochromic materials. Here, a new rational strategy of anion-directed folding a flexible cation (H2imb)2+ ((H2imb)2+ = di-protonated 2,3-bis(imidazolin-2-yl)-2,3-dimethylbutane) has been developed. Electron-donating Cl− and (ZnCl4)2− are used to direct folding a flexible electron-deficient (H2imb)2+ cation. Three complexes (H2imb)(NO3)2 (1), (H2imb)Cl2·H2O (2), and (H2imb)ZnCl4 (3) have been synthesized in which (H2imb)2+ crystallize in an anti-conformation, 88.8°-gauche, and 51.8°-gauche, respectively. In contrary to X-ray silent complex 1, X-ray induced photochromism has been achieved in both complex 2 and 3. An intermolecular charge-transfer mechanism has been elucidated and the anion directed folding of (H2imb)2+ has been validated to be critical to yield colored long-lived charge-separated states.

    DOI: 10.1016/j.cclet.2023.109052

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  • Photosynthesis of NH3 from NO3– using CH4 in Homogenous Re Catalysis at Room Temperature and Normal Pressure

    Genta Nakamura, Masaya Sakurai, Yohei Kametani, Yudai Kawasaki, Yoshihito Shiota, Kazunari Yoshizawa, Seiji Ogo, Takahiro Matsumoto

    ChemRxiv   2024.8

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    DOI: 10.26434/chemrxiv-2024-mzzcr

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  • Efficient Synthesis and Structural Analysis of Chiral 4,4′-Biazulene

    Ryoji Hatakenaka, Nanami Nishikawa, Yuji Mikata, Hiroki Aoyama, Kohsuke Yamashita, Yoshihito Shiota, Kazunari Yoshizawa, Yuuya Kawasaki, Katsuhiko Tomooka, Shin Kamijo, Fumito Tani, Toshihiro Murafuji

    Chemistry - A European Journal   30 ( 24 )   e202400098   2024.4   ISSN:0947-6539 eISSN:1521-3765

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    4,4′-Biazulene is a potentially attractive key component of an axially chiral biaryl compound, however, its structure and properties have not been clarified owing to the lack of its efficient synthesis. We report a breakthrough in the reliable synthesis of 4,4′-biazulene, which is achieved by the access to azulen-4-ylboronic acid pinacol ester and 4-iodoazulene as novel key synthetic intermediates for the Suzuki-Miyaura cross-coupling reaction. The X-ray crystallographic analysis of 4,4′-biazulene confirmed its axial chirality. The enantiomers of 4,4′-biazulene were successfully resolved by HPLC on the chiral stationary phase column. The kinetic experiments and DFT calculations indicate that the racemization energy barrier of 4,4′-biazulene is comparable to that of 1,1′-binaphthyl.

    DOI: 10.1002/chem.202400098

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  • Polar Crystals Using Molecular Chirality: Pseudosymmetric Crystallization toward Polarization Switching Materials

    Shinji Kanegawa, Shu-Qi Wu, Ziqi Zhou, Yoshihito Shiota, Takumi Nakanishi, Kazunari Yoshizawa, Osamu Sato

    Journal of the American Chemical Society   146 ( 16 )   11553 - 11561   2024.4   ISSN:0002-7863 eISSN:1520-5126

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    Polar compounds with switchable polarization properties are applicable in various devices such as ferroelectric memory and pyroelectric sensors. However, a strategy to prepare polar compounds has not been established. We report a rational synthesis of a polar CoGa crystal using chiral cth ligands (SS-cth and RR-cth, cth = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane). Both the original homo metal Co crystal and Ga crystal exhibit a centrosymmetric isostructure, where the dipole moment of metal complexes with the SS-cth ligand and those with the RR-cth ligand are canceled out. To obtain a polar compound, the Co valence tautomeric complex with SS-cth in the homo metal Co crystal is replaced with the Ga complex with SS-cth by mixing Co valence tautomeric complexes with RR-cth and Ga complexes with SS-cth. The CoGa crystal exhibits polarization switching between the pseudononpolar state at a low temperature and the polar state at a high temperature because only Co complexes exhibit changes in electric dipole moment due to metal-to-ligand charge transfer. Following the same strategy, the polarization-switchable CoZn complex was synthesized. The CoZn crystal exhibits polarization switching between the polar state at a low temperature and the pseudononpolar state at a high temperature, which is the opposite temperature dependence to that of the CoGa crystal. These results revealed that the polar crystal can be synthesized by design, using a chiral ligand. Moreover, our method allows for the control of temperature-dependent polarization changes, which contrasts with typical ferroelectric compounds, in which the polar ferroelectric phase typically occurs at low temperatures.

    DOI: 10.1021/jacs.4c02882

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  • Cyclopropanation Using Electrons Derived from Hydrogen: Reaction of Alkenes and Hydrogen without Hydrogenation

    Seiji Ogo, Takeshi Yatabe, Keishi Miyazawa, Yunosuke Hashimoto, Chiaki Takahashi, Hidetaka Nakai, Yoshihito Shiota

    JACS Au   4 ( 4 )   1615 - 1622   2024.3   ISSN:2691-3704 eISSN:2691-3704

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    Have you ever imagined reactions of alkenes with hydrogen that result in anything other than hydrogenation or hydrogenative C-C coupling? We have long sought to develop not only hydrogenation catalysts that activate H2 as hydride ions but also electron transfer catalysts that activate H2 as a direct electron donor. Here, we report the reductive cyclopropanation of alkenes using an iridium electron storage catalyst with H2 as the electron source without releasing metal waste from the reductant. We discuss the catalytic mechanism with selectivity to give the trans-isomer. These findings are based on the isolation of three complexes and density functional theory calculations.

    DOI: 10.1021/jacsau.4c00098

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  • Solvatochromism of a saddle-distorted cationic Zn(II)-porphyrin complex

    Hidemi Ochiai, Tomoya Ishizuka, Hiro Tanaka, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    Journal of Porphyrins and Phthalocyanines   28 ( 3 )   151 - 156   2024.3   ISSN:1088-4246 eISSN:1099-1409

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    Language:Others   Publishing type:Research paper (scientific journal)   Publisher:Journal of Porphyrins and Phthalocyanines  

    A saddle-distorted and cationic Zn(II)-porphyrin complex was revealed to exhibit solvatochromism in organic solvents, depending on the donor numbers. The color change was derived from the alteration of the HOMO-LUMO gap caused by the distortion of the porphyrin mean plane due to solvent coordination.

    DOI: 10.1142/S108842462450007X

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  • Neutral Nazarov reaction using protic solvents as activators

    Takayuki Iwata, Shingo Funatsu, Kohei Kajiwara, Yoshihito Shiota, Kazunari Yoshizawa, Mitsuru Shindo

    Bulletin of the Chemical Society of Japan   97 ( 2 )   2024.2   ISSN:0009-2673 eISSN:1348-0634

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    Herein, we report a neutral Nazarov reaction using protic solvents instead of strong acids as activators. The key to the success of this reaction lies in the rational design of the divinyl ketone substrates. In particular, the introduction of electron-donating groups (EDGs) at the β- and β′-positions of the carbonyl group in the divinyl ketone increases the Lewis basicity dramatically, an EDG at α-position promotes the cyclization, and the presence of a phenoxy group at β-position enables the irreversible elimination of phenol from the cyclized intermediate, thus shifting the reversible cyclization to the product side. This phenol-releasing reaction can be applied to clip chemistry to target acidic biological environments.

    DOI: 10.1093/BULCSJ/UOAD014

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  • A rhodium(<scp>ii</scp>)/rhodium(<scp>iii</scp>) redox couple for C–H bond amination with alkylazides: a rhodium(<scp>iii</scp>)–nitrenoid intermediate with a tetradentate [14]-macrocyclic ligand Reviewed International journal

    Hideki Sugimoto, Megumu Sakaida, Yoshihito Shiota, Mayuko Miyanishi, Yuma Morimoto, Kazunari Yoshizawa, Shinobu Itoh

    Dalton Trans.   53 ( 4 )   1607 - 1615   2024.1   ISSN:1477-9226 eISSN:1477-9234

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Royal Society of Chemistry (RSC)  

    The catalytic activity of a rhodium(ii) dimer complex, [Rh<sup>II</sup>(TMAA)]<sub>2</sub> (TMAA = tetramethyltetraaza[14]annulene), in C–H amination reactions with organic azides is explored.

    DOI: 10.1039/d3dt03429a

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  • Enhancement of Reactivity of a RuIV-Oxo Complex in Oxygen-Atom-Transfer Catalysis by Hydrogen-Bonding with Amide Moieties in the Second Coordination Sphere

    Tomoya Ishizuka, Taichi Kogawa, Chisato Ogawa, Hiroaki Kotani, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    JACS Au   3 ( 10 )   2813 - 2825   2023.10   eISSN:2691-3704

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    We have synthesized and characterized a RuII-OH2 complex (2), which has a pentadentate ligand with two pivalamide groups as bulky hydrogen-bonding (HB) moieties in the second coordination sphere (SCS). Complex 2 exhibits a coordination equilibrium through the coordination of one of the pivalamide oxygens to the Ru center in water, affording a η6-coordinated complex, 3. A detailed thermodynamic analysis of the coordination equilibrium revealed that the formation of 3 from 2 is entropy-driven owing to the dissociation of the axial aqua ligand in 2. Complex 2 was oxidized by a CeIV salt to produce the corresponding RuIII(OH) complex (5), which was characterized crystallographically. In the crystal structure of 5, hydrogen bonds are formed among the NH groups of the pivalamide moieties and the oxygen atom of the hydroxo ligand. Further 1e--oxidation of 5 yields the corresponding RuIV(O) complex, 6, which has intramolecular HB of the oxo ligand with two amide N-H protons. Additionally, the RuIII(OH) complex, 5, exhibits disproportionation to the corresponding RuIV(O) complex, 6, and a mixture of the RuII complexes, 2 and 3, in an acidic aqueous solution. We investigated the oxidation of a phenol derivative using complex 6 as the active species and clarified the switch of the reaction mechanism from hydrogen-atom transfer at pH 2.5 to electron transfer, followed by proton transfer at pH 1.0. Additionally, the intramolecular HB in 6 exerts enhancing effects on oxygen-atom transfer reactions from 6 to alkenes such as cyclohexene and its water-soluble derivative to afford the corresponding epoxides, relative to the corresponding RuIV(O) complex (6′) lacking the HB moieties in the SCS.

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  • Mechanisms of Co<inf>2</inf>L<inf>8</inf> (L = CO, CNR)-Catalyzed Hydrosilylation of Alkenes: A Theoretical Study

    Hideo Nagashima, Yoshihito Shiota, Kazunari Yoshizawa

    Organometallics   42 ( 20 )   2963 - 2972   2023.10   ISSN:0276-7333 eISSN:1520-6041

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    For the hydrosilylation of alkenes catalyzed by Co2L8 (L = CO, CNR), the Type II Chalk-Harrod cycle (the CH-II cycle) starting from HCoL4 ([2H]L) and the Type II modified Chalk-Harrod cycle (the mCH-II cycle) from Me3SiCoL4 ([2Si]L) have been proposed as the reaction mechanisms, but neither mechanism is fully consistent with the experimental results. Density functional theory (DFT) calculations verified the reaction pathways of the two catalytic cycles, leading to the conclusion that the behavior of CNR as a ligand is similar to that of CO in catalysis, and a comparison of the activation energies of the rate-determining step of the two cycles suggests that the mCH-II cycle is more favorable. The mCH-II mechanism contradicts the following three experimental results: [2Si]L is not catalytically active without photolysis; vinylsilane is not formed; and facile alkene isomerization occurs. These discrepancies were resolved by assuming that both HCoL3 ([3H]L) and Me3SiCoL3 ([3Si]L) generated from [2H]L were present in the system and acted as catalysts; [3H]L was responsible for the alkene isomerization and thermal generation of [3Si]L, whereas [3Si]L initiated the hydrosilylation of alkenes through the mCH-II cycle. Vinylsilanes could be formed from an intermediate in the mCH-II cycle; however, this pathway is thermodynamically unfavorable.

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  • Mechanistic Study of Reduction of Nitrite to NO by the Copper(II) Complex: Different Concerted Proton-Electron Transfer Reactivity between Nitrite and Nitro Complexes

    Yohei Kametani, Kei Ikeda, Kazunari Yoshizawa, Yoshihito Shiota

    Inorganic Chemistry   62 ( 34 )   13765 - 13774   2023.8   ISSN:0020-1669 eISSN:1520-510X

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    The literature contains numerous reports of copper complexes for nitrite (NO2-) reduction. However, details of how protons and electrons arrive and how nitric oxide (NO) is released remain unknown. The influence of the coordination mode of nitrite on reactivity is also under debate. Kundu and co-workers have reported nitrite reduction by a copper(II) complex [J. Am. Chem. Soc. 2020, 142, 1726-1730]. In their report, the copper(II) complex reduced nitrite using a phenol derivative as a reductant, resulting in NO, a hydroxyl copper(II) complex, and the corresponding biphenol. Also, the involvement of proton-coupled electron transfer was proposed by mechanistic studies. Herein, density functional theory calculations were performed to determine a mechanism for reduction of nitrite by a copper(II) complex. As a result of geometry optimization of an initial complex, two possible structures were obtained: Cu-ONO and Cu-NO2. Two possible reaction pathways initiated from Cu-ONO or Cu-NO2 were then considered. The calculation results indicated that the Cu-ONO pathway is energetically favorable. When changes in the electronic structure were considered, both pathways were found to involve concerted proton-electron transfer (CPET). In addition, an intrinsic reaction coordinate analysis revealed that the two pathways were achieved by different types of CPET. Furthermore, an intrinsic bond orbital analysis clearly indicated that, in the Cu-ONO pathway, the chemical events involved proceeded concertedly yet asynchronously.

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  • Intramolecular Hiyama Coupling: Synthesis of 1,8,13-Trisubstituted Chiral Triptycenes with Three Different Substituents by Intramolecular Substituent Transfer

    Takayuki Iwata, Masato Hanada, Satoru Kumagai, Tatsuro Yoshinaga, Yoshihito Shiota, Kazunari Yoshizawa, Mitsuru Shindo

    Chemistry - A European Journal   29 ( 39 )   e202300988   2023.7   ISSN:0947-6539 eISSN:1521-3765

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    Herein, we describe Hiyama coupling via intramolecular substituent transfer from silicon on one blade of triptycenes to another to yield 1,8,13-trisubstituted chiral triptycenes. This reaction is attributed to the proximity effect of substituents on triptycene, which plays an important role in not only the formation of the oxy-palladacycle but also the activation of the silyl group to facilitate σ-bond metathesis. After bromination and nucleophilic ring opening, the second intramolecular Hiyama coupling provided various 1,8,13-trisubstituted chiral triptycenes. The optical resolution of 1,8,13-triptycene afforded an optically active form for the first time.

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  • Effect of Macrocycles on the Photochemical and Electrochemical Properties of Cobalt-Dehydrocorrin Complex: Formation and Investigation of Co(I) Species

    Keita Shichijo, Yohei Kametani, Yoshihito Shiota, Kazunari Yoshizawa, Mamoru Fujitsuka, Hisashi Shimakoshi

    Inorganic Chemistry   62 ( 30 )   11785 - 11795   2023.6   ISSN:0020-1669 eISSN:1520-510X

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    Co(II)-pyrocobester (P-Co(II)), a dehydrocorrin complex, was semisynthesized from vitamin B12 (cyanocobalamin), and its photochemical and electrochemical properties were investigated and compared to those of the cobester (C-Co(II)), the cobalt-corrin complex. The UV-vis absorptions of P-Co(II) in CH2Cl2, ascribed to the π-π* transition, were red-shifted compared to those of C-Co(II) due to the π-expansion of the macrocycle in the pyrocobester. The reversible redox couple of P-Co(II) was observed at E1/2 = −0.30 V vs Ag/AgCl in CH3CN, which was assigned to the Co(II)/Co(I) redox couple by UV-vis, ESR, and molecular orbital analysis. This redox couple was positively shifted by 0.28 V compared to that of C-Co(II). This is caused by the high electronegativity of the dehydrocorrin macrocycle, which was estimated by DFT calculations for the free-base ligands. The reactivity of the Co(I)-pyrocobester (P-Co(I)) was evaluated by the reaction with methyl iodide in CV and UV-vis to form a photosensitive Co(III)-CH3 complex (P-Co(III)-CH3). The properties of the excited state of P-Co(I), *Co(I), were also investigated by femtosecond transient absorption (TA) spectroscopy. The lifetime of *Co(I) was estimated to be 29 ps from the kinetic trace at 587 nm. The lifetime of *Co(I) became shorter in the presence of Ar-X, such as iodobenzonitrile (1a), bromobenzonitrile (1b), and chlorobenzonitrile (1c), and the rate constants of electron transfer (ET) between the *Co(I) and Ar-X were determined to be 2.9 × 1011 M-1 s-1, 4.9 × 1010 M-1 s-1, and 1.0 × 1010 M-1 s-1 for 1a, 1b, and 1c, respectively.

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  • Site-selective radical reactions of kinetically stable open-shell singlet diradicaloid difluorenoheteroles with tributyltin hydride and azo-based radical initiators

    Naoki Tabata, Takumi Uchino, Chitoshi Kitamura, Kazunari Yoshizawa, Yoshihito Shiota, Shin Ichiro Kato

    Chemical Science   14 ( 22 )   5974 - 5982   2023.5   ISSN:2041-6520 eISSN:2041-6539

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    We have demonstrated site-selective radical reactions of the kinetically stable open-shell singlet diradicaloids difluoreno[3,4-b:4′,3′-d]thiophene (DFTh) and difluoreno[3,4-b:4′,3′-d]furan (DFFu) with tributyltin hydride (HSn(n-Bu)3) and azo-based radical initiators. Treatment of these diradicaloids with HSn(n-Bu)3 induces hydrogenation at the ipso-carbon in the five-membered rings, while treatment with 2,2′-azobis(isobutyronitrile) (AIBN) induces substitution at the carbon atoms in the peripheral six-membered rings. We have also developed one-pot substitution/hydrogenation reactions of DFTh/DFFu with various azo-based radical initiators and HSn(n-Bu)3. The resulting products can be converted into substituted DFTh/DFFu derivatives via dehydrogenation. Theoretical calculations unveiled a detailed mechanism of the radical reactions of DFTh/DFFu with HSn(n-Bu)3 and with AIBN, and that the site-selectivity of these radical reactions is controlled by the balance of the spin density and the steric hindrance in DFTh/DFFu.

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  • Selective methane oxidation by molecular iron catalysts in aqueous medium

    Hiroto Fujisaki, Tomoya Ishizuka, Hiroaki Kotani, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    Nature   616 ( 7957 )   476 - 481   2023.4   ISSN:0028-0836 eISSN:1476-4687

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    Using natural gas as chemical feedstock requires efficient oxidation of the constituent alkanes—and primarily methane1,2. The current industrial process uses steam reforming at high temperatures and pressures3,4 to generate a gas mixture that is then further converted into products such as methanol. Molecular Pt catalysts5–7 have also been used to convert methane to methanol8, but their selectivity is generally low owing to overoxidation—the initial oxidation products tend to be easier to oxidize than methane itself. Here we show that N-heterocyclic carbene-ligated FeII complexes with a hydrophobic cavity capture hydrophobic methane substrate from an aqueous solution and, after oxidation by the Fe centre, release a hydrophilic methanol product back into the solution. We find that increasing the size of the hydrophobic cavities enhances this effect, giving a turnover number of 5.0 × 102 and a methanol selectivity of 83% during a 3-h methane oxidation reaction. If the transport limitations arising from the processing of methane in an aqueous medium can be overcome, this catch-and-release strategy provides an efficient and selective approach to using naturally abundant alkane resources.

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  • Safe, One-Pot, Homogeneous Direct Synthesis of H2O2

    Ogo, S; Yatabe, T; Tome, T; Takenaka, R; Shiota, Y; Kato, K

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   145 ( 8 )   4384 - 4388   2023.3   ISSN:0002-7863 eISSN:1520-5126

  • Safe, One-Pot, Homogeneous Direct Synthesis of H2O2

    Seiji Ogo, Takeshi Yatabe, Tamon Tome, Riko Takenaka, Yoshihito Shiota, Kenji Kato

    Journal of the American Chemical Society   145 ( 8 )   4384 - 4388   2023.2   ISSN:00027863 eISSN:20462069

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    This paper reports the first example of a reductive C(sp^3)–C(sp^3) homo-coupling of benzyl/allyl halides in aqueous solution by using H_2 as an electron source {turnover numbers (TONs) = 0.5–2.3 for 12 h}. This homo-coupling reaction, promoted by visible light, is catalysed by a water-soluble electron storage catalyst (ESC). The reaction mechanism, and four requirements to make it possible, are also described.

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  • A Computational Study on the Mechanism of Catalytic Cyclopropanation Reaction with Cobalt N-Confused Porphyrin: The Effects of Inner Carbon and Intramolecular Axial Ligand

    Osamu Iwanaga, Mayuko Miyanishi, Toshihiro Tachibana, Takaaki Miyazaki, Yoshihito Shiota, Kazunari Yoshizawa, Hiroyuki Furuta

    Molecules   27 ( 21 )   7266 - 7266   2022.10   eISSN:1420-3049

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    The factors that affect acceleration and high trans/cis selectivity in the catalytic cyclopropanation reaction of styrene with ethyl diazoacetate by cobalt N-confused porphyrin (NCP) complexes were investigated using density functional theory calculations. The reaction rate was primarily related to the energy gap between the cobalt–carbene adduct intermediates, A and B, which was affected by the NCP skeletons and axial pyridine ligands more than the corresponding porphyrin complex. In addition, high trans/cis stereoselectivity was determined at the TS1 and, in part, in the isomerization process at the carbon-centered radical intermediates, Ctrans and Ccis.

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  • Spontaneous Assembly and Three‐Dimensional Stacking of Antiaromatic 5,15‐Dioxaporphyrin on HOPG

    Tsang-Wei Matt Chen, Yuki Tanaka, Yohei Kametani, Kum-Yi Cheng, Chih-Hsun Lin, Yi Rick Lin, Ting-Rong Hsu, Zuqian Chen, Jiping Hao, Shigeki Mori, Yoshihito Shiota, Kazunari Yoshizawa, Hiroyuki Furuta, Soji Shimizu, Chun-hsien Chen

    Angewandte Chemie International Edition   61 ( 48 )   e202212726   2022.10   ISSN:14337851 eISSN:15213773

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    Antiaromatic compounds have recently received considerable attention because of their novel properties such as narrow HOMO–LUMO gaps and facile formation of mutual stacking. Here, the spontaneous assembly of antiaromatic meso-2-thienyl-substituted 5,15-dioxaporphyrin (DOP-1) is scrutinized at the liquid-solid interface by scanning tunneling microscopy (STM). Polymorphism in monolayers characterized by the orthogonal and parallel assemblies is found at the low concentration of 0.05 mM. The parallel assembly is more stable and dominantly formed at higher concentrations. Aggregation was observed at concentrations >0.2 mM, and the STM images of the aggregates implied the formation of stacked layers. The intrinsic electronic structures of the mutually stacked bilayer generated by applying an electric pulse to the monolayer were probed by scanning tunneling spectroscopy to reveal the narrowing of the HOMO–LUMO gap by about 20 % compared with the monolayer, thus suggesting significant molecular orbital interactions.

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  • Importance of steric bulkiness of iridium photocatalysts with PNNP tetradentate ligands for CO<sub>2</sub> reduction Reviewed

    Kenji Kamada, Jieun Jung, Yohei Kametani, Taku Wakabayashi, Yoshihito Shiota, Kazunari Yoshizawa, Seong Hee Bae, Manami Muraki, Masayuki Naruto, Keita Sekizawa, Shunsuke Sato, Takeshi Morikawa, Susumu Saito

    Chemical Communications   58 ( 66 )   9218 - 9221   2022.8   ISSN:1359-7345 eISSN:1364-548X

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    Steric bulkiness – the metric of the robustness of the self-photosensitized, single metal-active-site catalysis, elucidated in CO<sub>2</sub> photoreduction.

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  • Mercury levels in hair are associated with reduced neurobehavioral performance and altered brain structures in young adults

    Takeuchi, H; Shiota, Y; Yaoi, K; Taki, Y; Nouchi, R; Yokoyama, R; Kotozaki, Y; Nakagawa, S; Sekiguchi, A; Iizuka, K; Hanawa, S; Araki, T; Miyauchi, CM; Sakaki, K; Nozawa, T; Ikeda, S; Yokota, S; Magistro, D; Sassa, Y; Kawashima, R

    COMMUNICATIONS BIOLOGY   5 ( 1 )   529   2022.6   eISSN:2399-3642

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  • Mechanistic Study for the Reaction of B-12 Complexes with m-Chloroperbenzoic Acid in Catalytic Alkane Oxidations

    Jiamin Cheng, Yoshihito Shiota, Mikako Yamasaki, Kureha Izukawa, Yoshimitsu Tachi, Kazunari Yoshizawa, Hisashi Shimakoshi

    INORGANIC CHEMISTRY   61 ( 25 )   9710 - 9724   2022.6   ISSN:0020-1669 eISSN:1520-510X

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    The oxidation of alkanes with m-chloroperbenzoic acid (mCPBA) catalyzed by the B12 derivative, heptamethyl cobyrinate, was investigated under several conditions. During the oxidation of cyclohexane, heptamethyl cobyrinate works as a catalyst to form cyclohexanol and cyclohexanone at a 0.67 alcohol to ketone ratio under aerobic conditions in 1 h. The reaction rate shows a firstorder dependence on the [catalyst] and [mCPBA] while being independent of [cyclohexane]; Vobs = k2[catalyst][mCPBA]. The kinetic deuterium isotope effect was determined to be 1.86, suggesting that substrate hydrogen atom abstraction is not dominantly involved in the rate-determining step. By the reaction of mCPBA and heptamethyl cobyrinate at low temperature, the corresponding cobalt(III)acylperoxido complex was formed which was identified by UV-vis, IR, ESR, and ESI-MS studies. A theoretical study suggested the homolysis of the O-O bond in the acylperoxido complex to form Co(III)-oxyl (Co-O center dot) and the m-chlorobenzoyloxyl radical. Radical trapping experiments using Ntert-butyl-alpha-phenylnitrone and CCl3Br, product analysis of various alkane oxidations, and computer analysis of the free energy for radical abstraction from cyclohexane by Co(III)-oxyl suggested that both Co(III)-oxyl and the m-chlorobenzoyloxyl radical could act as hydrogen-atom transfer reactants for the cyclohexane oxidation.

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  • Light-driven oxidation of CH<sub>4</sub> to C<sub>1</sub> chemicals catalysed by an organometallic Ru complex with O<sub>2</sub> Reviewed

    Tatsuya Nakano, Tsukasa Abe, Takahiro Matsumoto, Kento Kimura, Genta Nakamura, Shinya Hayami, Yoshihito Shiota, Kazunari Yoshizawa, Seiji Ogo

    RSC Advances   12 ( 20 )   12253 - 12257   2022.4   eISSN:2046-2069

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    We have achieved aerobic transformation of methane to C<sub>1</sub> chemicals catalysed by a homogeneous organometallic catalyst with light energy input.

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  • Light-driven oxidation of CH4 to C1 chemicals catalysed by an organometallic Ru complex with O2 Invited Reviewed International journal

    Nakano, T., Abe, T., Matsumoto, T., Kimura, K., Nakamura, G., Hayami, S., Shiota, Y., Yoshizawa, K. Ogo, S.

    RSC Advances.   12 ( 20 )   12253 - 12257   2022.4

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  • Mechanistic study on reduction of nitric oxide to nitrous oxide using a dicopper complex Reviewed

    Yohei Kametani, Tsukasa Abe, Kazunari Yoshizawa, Yoshihito Shiota

    Dalton Transactions   51 ( 14 )   5399 - 5403   2022.3   ISSN:1477-9226 eISSN:1477-9234

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    A density functional theory study was carried out to investigate the reduction mechanisms of NO to N2O using a dicopper complex reported by Zhang and coworkers (J. Am. Chem. Soc., 2019, 141, 10159-10164). The reaction mechanism consists of three steps: N-N bond formation, isomerization of the resultant N2O2 moiety, and cleavage of the N-O bond.

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  • Synthesis, redox properties, and catalytic hydrogen gas generation of porphycene cobalt complexes Reviewed

    Zihan Zhou, Taro Koide, Yoshihito Shiota, Yoshio Yano, Ning Xu, Toshikazu Ono, Hisashi Shimakoshi, Kazunari Yoshizawa, Yoshio Hisaeda

    Journal of Porphyrins and Phthalocyanines   26 ( 3 )   263 - 272   2022.3   ISSN:1088-4246 eISSN:1099-1409

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    A new meso-tetrakis(3,5-di-tert-butylphenyl) substituted porphycene and its cobalt complex were synthesized and characterized. Several meso-tetraarylporphycene cobalt complexes having different substituents showed catalytic activity for the hydrogen gas evolution reaction (HER) in the presence of trifluoroacetic acid (TFA) under electrochemical reductive conditions. The electrochemical potential of the HER was -1.50V vs. Ag/AgCl in THF. The active species of this reaction were determined to be the ligand reduced species of Co(II) porphycenes. The catalytic efficiencies of the cobalt complexes of meso-aryl substituted porphycenes and meso-tetraphenylporphyrin were compared and meso-tetraphenyl porphycene cobalt complex exhibited the best current efficiency of 72%. Based on these experimental results and theoretical calculations, we proposed a possible HER mechanism of this system.

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  • Augmented Self-Association by Electrostatic Forces in Thienopyrrole-Fused Thiadiazoles that Contain an Ester instead of an Ether Linker Reviewed

    Yukako Naito, Ryo Moriguchi, Chitoshi Kitamura, Taisuke Matsumoto, Toshitada Yoshihara, Tsutomu Ishi-i, Yuka Nagata, Hiroki Takeshita, Kazunari Yoshizawa, Yoshihito Shiota, Kazumasa Suzuki, Shin ichiro Kato

    Chemistry - An Asian Journal   17 ( 4 )   e202101341   2022.2   ISSN:1861-4728 eISSN:1861-471X

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    During the self-assembly of π-conjugated molecules, linkers and substituents can potentially add supportive noncovalent intermolecular interactions to π-stacking interactions. Here, we report the self-assembly behavior of thienopyrrole-fused thiadiazole (TPT) fluorescent dyes that possess ester or ether linkers and dodecyloxy side chains in solution and the condensed phase. A comparison of the self-association behavior of the ester- and ether-bridged compounds in solution using detailed UV-vis, fluorescence, and NMR spectroscopic studies revealed that the subtle replacement of the ether linkers by ester linkers leads to a distinct increase in the association constant (ca. 3–4 fold) and the enthalpic contribution (ca. 3 kcal mol−1). Theoretical calculations suggest that the ester linkers, which are in close proximity to one another due to the π-stacking interactions, induce attractive electrostatic forces and augment self-association. The self-assembly of TPT dyes into well-defined 1D clusters with high aspect ratios was observed, and their morphologies and crystallinity were investigated using SEM and X-ray diffraction analyses. TPTs with ester linkers exhibit a columnar liquid crystalline mesophase in the condensed phase.

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  • Importance of steric bulkiness of iridium photocatalysts with PNNP tetradentate ligands for CO2 reduction Reviewed International journal

    Kamada, K., Jung, J., Kametani, Y., Wakabayashi, T., Shiota, Y., Yoshizawa, K., Bae, S. H., Muraki, M., Naruto, M., Sekizawa, K., Sato, S., Morikawa, T. Saito, S.

    Chemical Communications.   58 ( 66 )   9218 - 9221   2022.1

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  • C(sp3)-H bond activation by the carboxylate-adduct of osmium tetroxide (OsO<inf>4</inf>) Reviewed

    Tomohiro Fujimoto, Yuka Hirata, Hideki Sugimoto, Mayuko Miyanishi, Yoshihito Shiota, Kazunari Yoshizawa, Shinobu Itoh

    Dalton Transactions   51 ( 3 )   1123 - 1130   2022.1   ISSN:1477-9226 eISSN:1477-9234

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    The reaction of osmium tetroxide (OsO4) and carboxylate anions (acetate: X- = AcO- and benzoate: X- = BzO-) gave 1 : 1 adducts, [OsO4(X)]- (1X), the structures of which were determined by X-ray crystallographic analysis. In both cases, the carboxylate anion X coordinates to the osmium centre to generate a distorted trigonal bipyramidal osmium(viii) complex. The carboxylate adducts show a negative shift of the redox potentials (E1/2) and a red shift of the νOsO stretches as compared to those of tetrahedral OsO4 itself. Despite the negative shift of E1/2, the reactivity of these adduct complexes 1X was enhanced compared to that of OsO4 in benzylic C(sp3)-H bond oxidation. The reaction obeyed the first-order kinetics on both 1X and the substrates, giving the second-order rate constant (k2), which exhibits a linear correlation with the C-H bond dissociation energy (BDEC-H) of the substrates (xanthene, 9,10-dihydroanthracene, fluorene and 1,2,3,4-tetrahydronaphthalene) and a kinetic deuterium isotope effect (KIE) of 9.7 (k2(xanthene-h2)/k2(xanthene-d2)). On the basis of these kinetic data together with the DFT calculation results, we propose a stepwise reaction mechanism involving rate-limiting benzylic hydrogen atom abstraction and subsequent rebound of the generated organic radical intermediate to a remaining oxido group on the osmium centre.

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  • Theoretical Investigation into Selective Benzene Hydroxylation by Ruthenium-Substituted Keggin-Type Polyoxometalates Reviewed

    Kei Ikeda, Kazunari Yoshizawa, Yoshihito Shiota

    Inorganic Chemistry   61 ( 1 )   10 - 14   2022.1   ISSN:0020-1669 eISSN:1520-510X

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    Benzene hydroxylation catalyzed by ruthenium-substituted Keggin-type polyoxometalates [RuV(O)XW11O39]n- (RuVOX; X = Al, Ga, Si, Ge, P, As, S; heteroatoms; 3 ≤ n ≤ 6) is investigated using the density functional theory approach. As a possible side reaction, the water oxidation reaction is also considered. We found that the rate-determining step for water oxidation by RuVOX requires a higher activation free energy than the benzene hydroxylation reaction, suggesting that all of the RuVOX catalysts show high chemoselectivity toward benzene hydroxylation. Additionally, the heteroatom effect in benzene hydroxylation by RuVOX is discussed. The replacement of Si by X induces changes in the bond length of μ4O-X, resulting in a change in the activation free energy for benzene hydroxylation by RuVOX. Consequentially, RuVOS is expected to be the most effective catalyst among the (RuVOX) catalysts for the benzene hydroxylation reaction.

    DOI: 10.1021/acs.inorgchem.1c02605

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  • Halide-Adducts of OsO<inf>4</inf>. Structure and Reactivity in Alcohol-Oxidation Reviewed

    Tomohiro Fujimoto, Yuka Hirata, Hideki Sugimoto, Mayuko Miyanishi, Yoshihito Shiota, Kazunari Yoshizawa, Shinobu Itoh

    Bulletin of the Chemical Society of Japan   95 ( 1 )   64 - 72   2022.1   ISSN:0009-2673 eISSN:1348-0634

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    Interaction of osmium tetroxide (OsO4) with a series of halide ions (X1 = I1, Br1, Cl1, and F1) is examined. Stable 1:1 adducts, [OsO4(X)]1 (1X), are formed in the case of Br1, Cl1, and F1, whereas redox reaction takes place with I1 to give [OsVIIO4]1 and I•. The adduct formation constant (KfX) increases as the basicity of the halide ion increases (Br1 < Cl1 < F1). Upon the adduct formation, the symmetric (¯(Os=O)sym) and asymmetric (¯(Os=O)asym) Os=O stretching vibration energies are lowered as compared with those of OsO4. The X-ray crystallographic analyses of the halide adducts indicate that the structural distortion of the osmium center from tetrahedron to trigonal bipyramid becomes larger as the KfX value becomes larger. 1F shows much higher reactivity compared with 1Br and 1Cl in the oxidation of benzyl alcohol to benzaldehyde, even though 1F has a lower reduction potential compared to 1Br and 1Cl. Mechanistic details of the alcohol oxidation reaction are evaluated by kinetic studies including Hammett analysis and kinetic deuterium isotope effect as well as by DFT calculations.

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  • Visualising Martensite Phase Fraction in Bulk Ferrite Steel by Superimposed Bragg-edge Profile Analysis of Wavelength resolved Neutron Transmission Imaging

    Sato, H; Kusumi, A; Shiota, Y; Hayashida, H; Su, YH; Parker, JD; Watanabe, K; Kamiyama, T; Kiyanagi, Y

    ISIJ INTERNATIONAL   62 ( 11 )   2319 - 2330   2022   ISSN:0915-1559 eISSN:1347-5460

  • Halide-Adducts of OsO<inf>4</inf>. Structure and Reactivity in Alcohol-Oxidation Reviewed International journal

    Tomohiro Fujimoto, Yuka Hirata, Hideki Sugimoto, Mayuko Miyanishi, Yoshihito Shiota, Kazunari Yoshizawa, Shinobu Itoh

    Bulletin of the Chemical Society of Japan   95 ( 1 )   64 - 72   2021.12

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    Interaction of osmium tetroxide (OsO4) with a series of halide ions (X1 = I1, Br1, Cl1, and F1) is examined. Stable 1:1 adducts, [OsO4(X)]1 (1X), are formed in the case of Br1, Cl1, and F1, whereas redox reaction takes place with I1 to give [OsVIIO4]1 and I•. The adduct formation constant (KfX) increases as the basicity of the halide ion increases (Br1 < Cl1 < F1). Upon the adduct formation, the symmetric (¯(Os=O)sym) and asymmetric (¯(Os=O)asym) Os=O stretching vibration energies are lowered as compared with those of OsO4. The X-ray crystallographic analyses of the halide adducts indicate that the structural distortion of the osmium center from tetrahedron to trigonal bipyramid becomes larger as the KfX value becomes larger. 1F shows much higher reactivity compared with 1Br and 1Cl in the oxidation of benzyl alcohol to benzaldehyde, even though 1F has a lower reduction potential compared to 1Br and 1Cl. Mechanistic details of the alcohol oxidation reaction are evaluated by kinetic studies including Hammett analysis and kinetic deuterium isotope effect as well as by DFT calculations.

  • Electrochemical Synthesis of Cyanoformamides from Trichloroacetonitrile and Secondary Amines Mediated by the B12Derivative Invited Reviewed International journal

    Mohammad Moniruzzaman, Yoshio Yano, Toshikazu Ono, Hisashi Shimakoshi, Yoshihito Shiota, Kazunari Yoshizawa, Yoshio Hisaeda

    Journal of Organic Chemistry   86 ( 22 )   16134 - 16143   2021.11

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  • Tin(II)–Nitrene Radical Complexes Formed by Electron Transfer from Redox-Active Ligand to Organic Azides and Their Reactivity in C(sp3)–H Activation Reviewed

    Hideki Sugimoto, Mayuka Yano, Kazunobu Sato, Mayuko Miyanishi, Kenji Sugisaki, Yoshihito Shiota, Akira Kaga, Kazunari Yoshizawa, Shinobu Itoh

    Inorganic Chemistry   60 ( 24 )   18603 - 18607   2021.11

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    A tin(II) complex coordinated by a sterically demanding o-phenylenediamido ligand is synthesized. The ligand is redox-active to reach a tin(II) complex with the diiminobenzosemiquinone radial anion in the oxidation by AgPF6. The tin(II) complex reacts with a series of nosylazides (x-NO2C6H4–SO2–N3; x = o, m, or p) at −30 °C to yield the corresponding nitrene radical bound tin(II) complexes. The nitrene radical complexes exhibit C(sp3)–H activation and amination reactivity.

    DOI: 10.1021/acs.inorgchem.1c02806

  • S,C,C- and O,C,C-Bridged Triarylamines and Their Persistent Radical Cations Reviewed

    Shunpei Kataoka, Shuichi Suzuki, Yoshihito Shiota, Kazunari Yoshizawa, Taisuke Matsumoto, Motoko S. Asano, Toshitada Yoshihara, Chitoshi Kitamura, Shin-ichiro Kato

    The Journal of Organic Chemistry   86 ( 18 )   12559 - 12568   2021.9

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    This work reports the synthesis, crystal structures, and electronic properties of structurally constrained S,C,C- and O,C,C-bridged triarylamine derivatives and their persistent radical cations. O,C,C-Bridged triphenylamines and a dinaphthylphenylamine were obtained through a straightforward synthetic protocol. Similar to a previously reported S,C,C-bridged triphenylamine, the O,C,C-bridged triarylamines were easily oxidized to afford the corresponding radical cations, which were obtained as hexachloroantimonate salts. X-ray crystallographic analyses showed almost planar structures for these O,C,C-bridged triarylamine radical cations, which represent new members of the family of planar triarylamine radical cations without substituents on the aryl rings. Detailed investigations of the electronic properties of the S,C,C- and O,C,C-bridged triarylamine radical cations demonstrated that the spin and positive charge are sufficiently delocalized over the planar triarylamine scaffolds. The results provide the following insights into the effects of the bridging unit (sulfur vs oxygen) and the dibenzo-annulation on the spin delocalization in the bridged triarylamine radical cations: (1) An effective decrease of the spin density on the nitrogen atom is observed for the sulfur bridge relative to the oxygen bridge; and (2) a moderate decrease of the spin density on the oxygen atom rather than the nitrogen atom is induced by the dibenzo-annulation.

    DOI: 10.1021/acs.joc.1c00969

  • Manipulating electron redistribution to achieve electronic pyroelectricity in molecular [FeCo] crystals. Reviewed International journal

    Pritam Sadhukhan, Shu-Qi Wu, Jeremy Ian Long, Takumi Nakanishi, Shinji Kanegawa, Kaige Gao, Kaoru Yamamoto, Hajime Okajima, Akira Sakamoto, Michael L Baker, Thomas Kroll, Dimosthenis Sokaras, Atsushi Okazawa, Norimichi Kojima, Yoshihito Shiota, Kazunari Yoshizawa, Osamu Sato

    Nature communications   12 ( 1 )   4836 - 4836   2021.8

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    Pyroelectricity plays a crucial role in modern sensors and energy conversion devices. However, obtaining materials with large and nearly constant pyroelectric coefficients over a wide temperature range for practical uses remains a formidable challenge. Attempting to discover a solution to this obstacle, we combined molecular design of labile electronic structure with the crystal engineering of the molecular orientation in lattice. This combination results in electronic pyroelectricity of purely molecular origin. Here, we report a polar crystal of an [FeCo] dinuclear complex exhibiting a peculiar pyroelectric behavior (a substantial sharp pyroelectric current peak and an unusual continuous pyroelectric current at higher temperatures) which is caused by a combination of Fe spin crossover (SCO) and electron transfer between the high-spin Fe ion and redox-active ligand, namely valence tautomerism (VT). As a result, temperature dependence of the pyroelectric behavior reported here is opposite from conventional ferroelectrics and originates from a transition between three distinct electronic structures. The obtained pyroelectric coefficient is comparable to that of polyvinylidene difluoride at room temperature.

    DOI: 10.1038/s41467-021-25041-4

  • Quadruple Role of Pd Catalyst in Domino Reaction Involving Aryl to Alkyl 1,5‐Pd Migration to Access 1,9‐Bridged Triptycenes Reviewed

    Takayuki Iwata, Satoru Kumagai, Tatsuro Yoshinaga, Masato Hanada, Yoshihito Shiota, Kazunari Yoshizawa, Mitsuru Shindo

    Chemistry – A European Journal   27 ( 45 )   11548 - 11553   2021.8

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    A Pd-catalyzed domino reaction of 1,8,13-tribromo-9-methoxytriptycenes is reported. Under conventional Suzuki coupling conditions, the triptycenes underwent multiple transformations to give 1,9-bridged triptycenes. Based on mechanistic investigations, a single Pd catalyst functions as Pd0, PdII and PdIV species to catalyze four distinct processes: (1) aryl to alkyl 1,5-Pd migration, (2) intramolecular arylation, (3) homocoupling of phenylboronic acid and (4) Suzuki coupling. DFT calculations revealed that 1,5-Pd migration likely proceeds via both concerted PdII and stepwise PdIV routes. Asymmetric synthesis of the chiral triptycenes, as well as optical resolution, and further transformation are also reported.

    DOI: 10.1002/chem.202101728

  • Mechanistic Insights into the Dicopper-Complex-Catalyzed Hydroxylation of Methane and Benzene Using Nitric Oxide: A DFT Study Reviewed

    Tsukasa Abe, Yohei Kametani, Kazunari Yoshizawa, Yoshihito Shiota

    Inorganic Chemistry   60 ( 7 )   4599 - 4609   2021.4

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    Although hydrocarbons are known to act as reductants for the catalytic reduction of nitric oxides (NOx) over copper-based catalysts, the reaction mechanism requires clarification. Herein, density functional theory (DFT) calculations were carried out to investigate the reduction mechanisms of NOx to dinitrogen coupled to the hydroxylation of methane or benzene using the dicopper complex reported by Zhang and co-workers [ J. Am. Chem. Soc. 2019, 141, 10159-10164 ]. The B3LYP functional was used to optimize the (μ-oxo)(μ-nitrosyl)dicopper complex in the quartet state and the (μ-η2:η2-NO2)dicopper complex in the doublet state, the latter of which was found to be the ground state. Then, we investigated the reactivities of the (μ- η2:η2-NO2)dicopper complex toward methane and benzene by considering the conversions of N2O to N2 in the presence and the absence of methane or benzene. In the presence of methane and benzene, the calculated activation energies were 27.0 and 21.0 kcal/mol, respectively, whereas that with N2O alone was prohibitively high (61.9 kcal/mol). Thus, the (μ- η2:η2-NO2)dicopper complex prefers the reactions with methane and benzene to that with N2O. The reaction of the (μ- η2:η2-NO2)dicopper complex with methane or benzene generated the (μ-nitrosyl)dicopper complex. The (μ-nitrosyl)dicopper complex then reacted with N2O to regenerate the (μ- η2:η2-NO2)dicopper complex and N2 with an activation barrier of 31.5 kcal/mol. The overall reactions for methane and benzene hydroxylation were calculated to be exothermic by 41.7 and 54.1 kcal/mol, respectively. These results suggest that the catalytic reduction of NOx using hydrocarbons is feasible at certain operating temperatures. Thus, our calculations provide new insights into the design of catalysts for NOx purification.

    DOI: 10.1021/acs.inorgchem.0c03558

  • One-Pot Synthesis of Tertiary Amides from Organic Trichlorides through Oxygen Atom Incorporation from Air by Convergent Paired Electrolysis Reviewed

    Zhongli Luo, Kenji Imamura, Yoshihito Shiota, Kazunari Yoshizawa, Yoshio Hisaeda, Hisashi Shimakoshi

    The Journal of Organic Chemistry   86 ( 8 )   5983 - 5990   2021.4

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    A convergent paired electrolysis catalyzed by a B12 complex for the one-pot synthesis of a tertiary amide from organic trichlorides (R-CCl3) has been developed. Various readily available organic trichlorides, such as benzotrichloride and its derivatives, chloroform, dichlorodiphenyltrichloroethane (DDT), trichloro-2,2,2-trifluoroethane (CFC-113a), and trichloroacetonitrile (CNCCl3), were converted to amides in the presence of tertiary amines through oxygen incorporation from air at room temperature. The amide formation mechanism in the paired electrolysis, which was mediated by a cobalt complex, was proposed.

    DOI: 10.1021/acs.joc.1c00161

  • Arylene-hexaynylene and -octaynylene macrocycles: Extending the polyyne chains drives self-association by enhanced dispersion force Invited Reviewed International journal

    Kato, S. I., Kumagai, R., Abe, T., Higuchi, C., Shiota, Y., Yoshizawa, K., Takahashi, N., Yamamoto, K., Hossain, M. Z., Hayashi, K., Hirose, T. Nakamura, Y.

    Chemical Communications.   57 ( 5 )   576 - 579   2021.1

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  • Oxygen Atom Insertion into the Osmium–Carbon Bond via an Organometallic Oxido–Osmium(V) Intermediate Reviewed

    Hideki Sugimoto, Kurumi Aoki, Mayuko Miyanishi, Yoshihito Shiota, Kazunari Yoshizawa, Shinobu Itoh

    Organometallics   40 ( 2 )   102 - 106   2021.1

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    A cyclometalated osmium(III) complex, [OsIIICl(phpy)(tpy)]+ (OsIII(phpy); phpy = 2-C6H4-2-C5H4N-κC,N) is synthesized from OsIIICl3(tpy) (tpy = 2,26,2″-terpyridine) and 2-phenylpyridine (H-phpy) in the presence of AgPF6, in which the metalated carbon atom is disposed trans to the chlorido ligand. Oxidation of OsIII(phpy) with oxygen atom transfer oxidants such as N-methylmorpholine N-oxide (NMO), N,N-dimethylaniline N-oxide (DMAO), H2O2, t-BuOOH, and m-chloroperoxybenzoic acid (m-CPBA) in CH3CN or electron transfer type oxidants such as (NH4)2S2O8 and ammonium hexanitratocerate (CAN) in H2O/acetone causes oxygen atom insertion between the osmium(III)-carbon bond to give a phenoxido-osmium(III) complex OsIII(O-phpy). Isotope labeling experiments using H218O and kinetic studies as well as calculation studies indicate formation of an organometallic oxido-osmium(V) complex as the active intermediate.

    DOI: 10.1021/acs.organomet.0c00772

  • Macroscopic Polarization Change via Electron Transfer in a Valence Tautomeric Cobalt Complex Reviewed

    Shu-Qi Wu, Meijiao Liu, Kaige Gao, Shinji Kanegawa, Yusuke Horie, Genki Aoyama, Hajime Okajima, Akira Sakamoto, Michael L. Baker, Myron S. Huzan, Peter Bencok, Tsukasa Abe, Yoshihito Shiota, Kazunari Yoshizawa, Wenhuang Xu, Hui-Zhong Kou, Osamu Sato

    Nature Communications   11 ( 1 )   2020.12

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    Polarization change induced by directional electron transfer attracts considerable attention owing to its fast switching rate and potential light control. Here, we investigate electronic pyroelectricity in the crystal of a mononuclear complex, [Co(phendiox)(rac-cth)](ClO4)·0.5EtOH (1·0.5EtOH, H2phendiox = 9, 10-dihydroxyphenanthrene, rac-cth = racemic 5, 5, 7, 12, 12, 14-hexamethyl-1, 4, 8, 11-tetraazacyclotetradecane), which undergoes a two-step valence tautomerism (VT). Correspondingly, pyroelectric current exhibits double peaks in the same temperature domain with the polarization change consistent with the change in dipole moments during the VT process. Time-resolved Infrared (IR) spectroscopy shows that the photo-induced metastable state can be generated within 150 ps at 190 K. Such state can be trapped for tens of minutes at 7 K, showing that photo-induced polarization change can be realized in this system. These results directly demonstrate that a change in the molecular dipole moments induced by intramolecular electron transfer can introduce a macroscopic polarization change in VT compounds.

    DOI: 10.1038/s41467-020-15988-1

  • Photocatalytic hydrogen evolution using a Ru(ii)-bound heteroaromatic ligand as a reactive site Reviewed

    Takuya Sawaki, Tomoya Ishizuka, Nanase Namura, Dachao Hong, Mayuko Miyanishi, Yoshihito Shiota, Hiroaki Kotani, Kazunari Yoshizawa, Jieun Jung, Shunichi Fukuzumi, Takahiko Kojima

    DALTON TRANSACTIONS   49 ( 47 )   17230 - 17242   2020.12

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    A Ru-II complex, [Ru-II(tpphz)(bpy)(2)](2+) (1) (tpphz = tetrapyridophenazine, bpy = 2,2 '-bipyridine), whose tpphz ligand has a pyrazine moiety, is converted efficiently to [Ru-II(tpphz-HH)(bpy)(2)](2+) (2) having a dihydropyrazine moiety upon photoirradiation of a water-methanol mixed solvent solution of 1 in the presence of an electron donor. In this reaction, the triplet metal-to-ligand charge-transfer excited state ((MLCT)-M-3*) of 1 is firstly formed upon photoirradiation and the (MLCT)-M-3* state is reductively quenched with an electron donor to afford [Ru-II(tpphz(-))(bpy)(2)](+), which is converted to 2 without the observation of detectable reduced intermediates by nano-second laser flash photolysis. The inverse kinetic isotope effect (KIE) was observed to be 0.63 in the N-H bond formation of 2 at the dihydropyrazine moiety. White-light (380-670 nm) irradiation of a solution of 1 in a protic solvent, in the presence of an electron donor under an inert atmosphere, led to photocatalytic H-2 evolution and the hydrogenation of organic substrates. In the reactions, complex 2 is required to be excited to form its (MLCT)-M-3* state to react with a proton and aldehydes. In photocatalytic H-2 evolution, the H-H bond formation between photoexcited 2 and a proton is involved in the rate-determining step with normal KIE being 5.2 on H-2 evolving rates. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations on the reaction mechanism of H-2 evolution from the ground and photo-excited states of 2 were performed to have a better understanding of the photocatalytic processes.

    DOI: 10.1039/d0dt03546g

  • Mechanistic Insight into Concerted Proton-Electron Transfer of a Ru(IV)-Oxo Complex: A Possible Oxidative Asynchronicity. Reviewed International journal

    Hiroaki Kotani, Hinatsu Shimomura, Kei Ikeda, Tomoya Ishizuka, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    Journal of the American Chemical Society   142 ( 40 )   16982 - 16989   2020.10

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    We have thoroughly investigated the oxidation of benzyl alcohol (BA) derivatives by a RuIV(O) complex (Ru
    IV
    (O)) in the absence or presence of Brønsted acids in order to elucidate the proton-coupled electron-transfer (PCET) mechanisms in C-H oxidation on the basis of a kinetic analysis. Oxidation of BA derivatives by Ru
    IV
    (O) without acids proceeded through concerted proton-electron transfer (CPET) with a large kinetic isotope effect (KIE). In contrast, the oxidation of 3,4,5-trimethoxy-BA ((MeO)3-BA) by Ru
    IV
    (O) was accelerated by the addition of acids, in which the KIE value reached 1.1 with TFA (550 mM), indicating an alteration of the PCET mechanism from CPET to stepwise electron transfer (ET) followed by proton transfer (PT). Although the oxidized products of BA derivatives were confirmed to be the corresponding benzaldehydes in the range of acid concentrations (0-550 mM), a one-electron-reduction potential of Ru
    IV
    (O) was positively shifted with increases in the concentrations of acids. The elevated reduction potential of Ru
    IV
    (O) strongly influenced the PCET mechanisms in the oxidation of (MeO)3-BA, changing the mechanism from CPET to ET/PT, as evidenced by the driving-force dependence of logarithms of reaction rate constants in light of the Marcus theory of ET. In addition, dependence of activation parameters on acid concentrations suggested that an oxidative asynchronous CPET, which is not an admixture of the CPET and ET/PT mechanisms, is probably operative in the boundary region (0 mM < [TFA] < 50 mM) involving a one-proton-interacted Ru
    IV
    (O)···H+ as a dominant reactive species.

    DOI: 10.1021/jacs.0c05738

  • Redox properties of a bipyrimidine-bridged dinuclear ruthenium(II) complex Reviewed

    Tomoya Ishizuka, Masaki Itogawa, Hinatsu Shimomura, Yoshihito Shiota, Hiroaki Kotani, Kazunari Yoshizawa, Takahiko Kojima

    INORGANIC CHEMISTRY COMMUNICATIONS   120   2020.10

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    A dinuclear Ru-II complex, [{(RuCl)-Cl-II(MeBPA)}(2)(mu-bpm)](PF6)(2) (1), exhibited three reversible redox waves at -0.75, + 0.91 and +1.15 V vs Ag/AgCl in acetone at -60 degrees C. The former wave can be assigned to the 1e(-)-reduction process of the bridging bpm ligand and the latter two are assigned to the stepwise 1e(-)-oxidation processes of the two Ru centers. Electrochemical oxidation of 1 afforded a "class I" mixed-valence (MV) state, in which the charge localizes on one of the two Ru centers. On the other hand, electrochemical 1e(-)-reduction of 1 predominantly proceeds on the bridging bpm ligand. The valence-localized MV state should be derived from a largely distorted structure of the Ru-II site to reduce the pi-back bonding from a filled Ru-II d pi orbital to the bpm ligand as suggested by DFT calculations.

    DOI: 10.1016/j.inoche.2020.108150

  • Selective catalytic 2e−-oxidation of organic substrates by an FeII complex having an N-heterocyclic carbene ligand in water Reviewed International journal

    Hiroto Fujisaki, Tomoya Ishizuka, Yoshihiro Shimoyama, Hiroaki Kotani, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    Chemical Communications   56 ( 68 )   9783 - 9786   2020.9

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    An FeII complex, 1, having a pentadentate ligand with an NHC moiety catalyzes substrate oxidation to afford 2e-oxidized products with high selectivity by suppression of overoxidation in water. A Bell-Evance-Polanyi plot for the substrate oxidation catalyzed by 1 exhibited an inflection point around 86 kcal mol-1, indicating strong C-H abstraction ability of the reactive species derived from 1.

  • Active catalyst for methane hydroxylation by an iridium-oxo complex Reviewed

    Kazunari Yoshizawa, Kei Ikeda, Muhammad Haris Mahyuddin, Yoshihito Shiota

    ACS Catalysis   10 ( 15 )   8254 - 8262   2020.8

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    Motivated by a recent study on [IrV(η5-C5H5){ppy}(O)]2+ (ppy is 2-phenylpryridine), which is able to cleave the C-H bond of decalin but not of methane due to a high activation energy of 25.7 kcal/mol (Zhou, M. et al. Cp∗ iridium Precatalysts for Selective C-H Oxidation via Direct Oxygen Insertion: A Joint Experimental/Computational Study. ACS Catal. 2012, 2, 208 218), in the present study, we perform density functional theory (DFT) calculations on another kind of an Ir-oxo complex, namely, [IrV(η5-C5Me5){bpy(COOH)2}(O)]2+ or OC, where bpy(COOH)2 is 2,2′-bipyridine-4,4′ dicarboxylic acid, to assess its ability to hydroxylate methane to methanol. OC is formed by light-induced oxidation of the Ir-H2O complex to generate electricity. By hydroxylating methane to methanol and inserting H2O, OC can regenerate the Ir-H2O complex and thus create a catalytic loop similar to a fuel cell. Herein, by utilizing intrinsic bond orbital (IBO) analysis, we show detailed mechanisms of how OC efficiently cleaves the strong C-H bond of methane to form methanol in three possible spin states, namely, the triplet, open-shell singlet, and closed-shell singlet states. In the triplet state, the C-H bond cleavage proceeds with an activation energy of only 11.3 kcal/mol via a hydrogen atom transfer mechanism, where an intermediate species involving •CH3 and Ir-OH• is formed in the same spin state, although a spin change to the open-shell singlet state is likely to occur. A subsequent HO-CH3 recombination occurs without a barrier through direct radical coupling in the open-shell singlet state. In contrast, the C-H bond cleavage in the closed-shell singlet state occurs via a hydride transfer (or oxygen insertion) mechanism, where methanol is directly formed without any intermediate states. Although this reaction mechanism requires a lower C-H activation energy (5.6 kcal/mol), OC in the closed-shell singlet state is less stable by 11.9 kcal/mol than that in the triplet state. These results provide a theoretical prediction of an alternative promising catalyst for the direct conversion of methane to methanol and the methane fuel cell.

    DOI: 10.1021/acscatal.0c01610

  • Anthranoxides as Highly Reactive Arynophiles for the Synthesis of Triptycenes Reviewed

    Takayuki Iwata, Mizuki Hyodo, Takuto Fukami, Yoshihito Shiota, Kazunari Yoshizawa, Mitsuru Shindo

    Chemistry – A European Journal   26 ( 39 )   8506 - 8510   2020.7

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    We report herein an efficient method to synthesize triptycenes by the reaction of benzynes and anthranoxides, which are electron-rich and readily prepared from the corresponding anthrones. Using this method, 1,9-syn-substituted triptycenes were regioselectively obtained employing 3-methoxybenzynes. This method was also applied to synthesize pentiptycenes. A DFT study revealed that the cycloaddition of lithium anthranoxide and benzyne proceeds stepwise.

    DOI: 10.1002/chem.202002065

  • Quenching and Restoration of Orbital Angular Momentum through a Dynamic Bond in a Cobalt(II) Complex Reviewed

    Sheng-Qun Su, Shu-Qi Wu, Michael L. Baker, Peter Bencok, Nobuaki Azuma, Yuji Miyazaki, Motohiro Nakano, Soonchul Kang, Yoshihito Shiota, Kazunari Yoshizawa, Shinji Kanegawa, Osamu Sato

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   142 ( 26 )   11434 - 11441   2020.7

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    Orbital angular momentum plays a vital role in various applications, especially magnetic and spintronic properties. Therefore, controlling orbital angular momentum is of paramount importance to both fundamental science and new technological applications. Many attempts have been made to modulate the ligand-field-induced quenching effects of orbital angular momentum to manipulate magnetic properties. However, to date, reported changes in the magnitude of orbital angular momentum are small in both molecular and solid-state magnetic materials. Moreover, no effective methods currently exist to modulate orbital angular momentum. Here we report a dynamic bond approach to realize a large change in orbital angular momentum. We have developed a Co(II) complex that exhibits coordination number switching between six and seven. This cooperative dynamic bond switching induces considerable modulation of the ligand field, thereby leading to substantial quenching and restoration of the orbital angular momentum. This switching mechanism is entirely different from those of spin-crossover and valence tautomeric compounds, which exhibit switching in spin multiplicity.

    DOI: 10.1021/jacs.0c02257

  • Theoretical Study of the Direct Conversion of Methane to Methanol Using H<inf>2</inf>O<inf>2</inf>as an Oxidant on Pd and Au/Pd Surfaces Reviewed

    P. K. Sajith, Aleksandar Staykov, Masataka Yoshida, Yoshihito Shiota, Kazunari Yoshizawa

    Journal of Physical Chemistry C   124 ( 24 )   13231 - 13239   2020.6

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    First-principle theoretical study was performed to elucidate the reaction mechanism of the direct conversion of methane to methanol using hydrogen peroxide as an oxidant over Pd and Au/Pd catalysts. We have investigated the effect of Au-Pd alloying and its effect on the reaction steps and energetics and we have provided an understanding of the contribution of surface-exposed Au centers to the overall reaction mechanism. The hydrogen peroxide decomposition reactions to OH groups or surface-adsorbed oxo species and water molecules were compared on the Pd and Au/Pd surfaces as an important preliminary process for the methane oxidation. We have evaluated the C-H bond cleavage energetics assisted by either the OH group or oxo species over Pd and Au/Pd surfaces and compared them to the C-H cleavage energy. Our results show that the products of hydrogen peroxide decomposition significantly reduce the high activation barrier for the hydrogen atom abstraction from methane. The recombination of methyl group and OH group was found to be the rate-determining step for the methanol formation. The proposed reaction pathway in our work provides important insights into the oxidation mechanism by hydrogen peroxide and the fine-tuning of the Pd catalyst by other alloying elements such as Au.

    DOI: 10.1021/acs.jpcc.0c03237

  • Theoretical rationalization for the equilibrium between (μ–η2:η2-peroxido)CuIICuII and bis(μ-oxido)CuIIICuIII complexes: perturbational effects from ligand frameworks Reviewed International journal

    Tsukasa Abe, Yoshihito Shiota, Shinobu Itoh, Kazunari Yoshizawa

    Dalton Transactions   49 ( 20 )   6710 - 6717   2020.5

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    DFT calculations are carried out to investigate the geometric effects of the supporting ligands in the relative energies of the (μ-η2:η2-peroxido)CuIICuII complex 1 and the bis(μ-oxido)CuIIICuIII complex 2. The N3-tridentate ligand bearing acyclic propane diamine framework La preferentially provided 1, whereas the N3-tridentate ligand with cyclic diamine framework such as 1,4-diazacycloheptane Lb gave 2 after the oxygenation of the corresponding CuI complexes as reported previously [S. Itoh, et al., Inorg. Chem., 2014, 53, 8786-8794]. Calculations at the B3LYP∗-D3 level of theory can reasonably explain the experimental results in relative energies, structures and harmonic frequencies of 1 and 2. Perturbational effects of the diamine chelates of La and Lb especially on the equilibrium of 1 and 2 are investigated in detail. In the range from 2.30 Å to 3.40 Å of the N-N distance in the diamine moiety, 1 is more stable than 2 by 8.4 kcal mol-1 at the distance of 3.40 Å. Calculated potential energies indicate that the decrease in the N-N distance is associated with a decrease in energy of 2, leading that 2 can be most stabilized at the N-N distance of 2.60 Å. Furthermore, molecular orbitals analyses are performed to explain that the energy gaps between the σ∗ orbital of the O-O bond and the dx2-y2 orbitals of the CuII ions of 1 get small as the diamine moiety is shrunk, leading to facilitate the O-O bond cleavage from 1 to 2.

  • Three‐step Spin State Transition and Hysteretic Proton Transfer in the Crystal of an Iron(II) Hydrazone Complex Reviewed

    Takumi Nakanishi, Yuta Hori, Shuqi Wu, Hiroyasu Sato, Atsushi Okazawa, Norimichi Kojima, Yusuke Horie, Hajime Okajima, Akira Sakamoto, Yoshihito Shiota, Kazunari Yoshizawa, Osamu Sato

    Angewandte Chemie International Edition   59 ( 35 )   14781 - 14787   2020.5

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    A proton–electron coupling system, exhibiting unique bistability or multistability of the protonated state, is an attractive target for developing new switchable materials based on proton dynamics. Herein, we present an iron(II) hydrazone crystalline compound, which displays the stepwise transition and bistability of proton transfer at the crystal level. These phenomena are realized through the coupling with spin transition. Although the multi-step transition with hysteresis has been observed in various systems, the corresponding behavior of proton transfer has not been reported in crystalline systems; thus, the described iron(II) complex is the first example. Furthermore, because proton transfer occurs only in one of the two ligands and π electrons redistribute in it, the dipole moment of the iron(II) complexes changes with the proton transfer, wherein the total dipole moment in the crystal was canceled out owing to the antiferroelectric-like arrangement.

    DOI: 10.1002/anie.202006763

  • Local Structures and Dynamics of Imidazole Molecules in Poly(vinylphosphonic acid)-Imidazole Composite Investigated by Molecular Dynamics Reviewed

    Yuta Hori, Toshiya Suetake, Yoshihito Shiota, Kazunari Yoshizawa, Yasuteru Shigeta, Tomonori Ida, Motohiro Mizuno

    ACS APPLIED POLYMER MATERIALS   2 ( 4 )   1561 - 1568   2020.4

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    The composite materials of acidic polymers and imidazole (Im) exhibit good high-proton conduction, making them potentially useful in proton-exchange membrane fuel cells. The proton conduction mechanism must be clearly elucidated for the design of future high proton-conduction materials. This study examines the local hydrogen-bonding structures and dynamics of Im for proton-conducting poly(vinylphosphonic acid)-Im (PVPA-xIm) composites by using molecular dynamics simulations. Radial distribution functions (RDFs) characterize the hydrogen bonds between Im or imidazolium cation (ImH(+)) and phosphonic acid (PA) groups and among Im molecules. RDFs and diffusion coefficients suggest that the intercalation of Im to PVPA reduces Im mobility because of the interaction between Im and PA groups. However, similar to pure Im, the amount of Im with fast rotational motions increases as the amount of Im increases. Our study leads us to conclude that long-range proton transport occurs through the hydrogen-bonding network of Im and that the fast rotational motions of Im enhance proton conduction in PVPA-xIm composites.

    DOI: 10.1021/acsapm.9b01222

  • Room-temperature activation of methane and direct formations of acetic acid and methanol on Zn-ZSM-5 zeolite: A mechanistic DFT study

    Muhammad Haris Mahyuddin, Seiya Tanaka, Yoshihito Shiota, Kazunari Yoshizawa

    Bulletin of the Chemical Society of Japan   93 ( 3 )   345 - 354   2020.3

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    DOI: 10.1246/BCSJ.20190282

  • Cover Feature: Mechanistic Study on Ring-Contracting Skeletal Rearrangement from Porphycene to Isocorrole by Experimental and Theoretical Methods (Eur. J. Org. Chem. 12/2020) Reviewed

    Taro Koide, Takafumi Maeda, Tsukasa Abe, Yoshihito Shiota, Yoshio Yano, Toshikazu Ono, Kazunari Yoshizawa, Yoshio Hisaeda

    European Journal of Organic Chemistry   2020 ( 12 )   1783 - 1783   2020.3

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    DOI: 10.1002/ejoc.202000226

  • Chemical transformations of push-pull fluorenones: Push-pull dibenzodicyanofulvenes as well as fluorenone- And dibenzodicyanofulvene-tetracyanobutadiene conjugates Invited Reviewed International journal

    Shin Ichiro Kato, Tomokazu Kijima, Yoshihito Shiota, Tsukasa Abe, Satoshi Kuwako, Hidenori Miyauchi, Naoki Yoshikawa, Koji Yamamoto, Kazunari Yoshizawa, Toshitada Yoshihara, Seiji Tobita, Yosuke Nakamura

    Organic and Biomolecular Chemistry   18 ( 22 )   4198 - 4209   2020.1

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    Push-pull fluorenones (FOs) were synthesized by treating a benzopentalenequinone (BPO) derivative with alkynes that bear an electron-rich aniline moietyviaa regioselective [4 + 2] cycloaddition (CA) followed by a [4 + 1] retrocycloaddition (RCA). The resulting FOs were readily converted into dibenzodicyanofulvenes (DBDCFs) by treatment with malononitrile in the presence of TiCl4and pyridine. The FOs and DBDCFs exhibit intramolecular charge-transfer (ICT) that manifests in absorptions at 350-650 nm and amphoteric electrochemical behavior. Furthermore, FOs and DBDCFs that contain a C-C bond react with tetracyanoethylene in a formal [2 + 2] CA followed by a retro-electrocyclization to afford sterically congested tetracyanobutadiene (TCBD) conjugates. The substituent (H or Me) on the aromatic ring adjacent to the butadiene moiety thereby determines whether the butadiene adopts an s-cisor s-transconformation, and thus controls the physicochemical properties of the resulting TCBDs. The TCBD conjugates exhibit ICT absorptions (≤800 nm) together with up to four reversible reduction steps.

  • Computational Study on the Light-Induced Oxidation of Iridium-Aqua Complex to Iridium-Oxo Complex over WO<inf>3</inf>(001) Surface Reviewed International journal

    Kei Ikeda, Muhammad Haris Mahyuddin, Yoshihito Shiota, Aleksandar Staykov, Takahiro Matsumoto, Seiji Ogo, Kazunari Yoshizawa

    Inorganic chemistry   59 ( 1 )   415 - 422   2020.1

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    An iridium aqua complex [IrIII(Ε5-C5Me5){bpy(COOH)2}(H2O)]2+ under visible light irradiation has been experimentally reported to form an iridium-oxo (Ir-oxo) complex [IrV(Ε5-C5Me5){bpy(COOH)2}(O)]2+, which oxidizes H2O to O2. However, the mechanism for the formation of this Ir-oxo complex remains unclear, due to the difficulties in observing the unstable Ir-oxo complex and computing light-induced systems having different numbers of electrons. In this study, we perform density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to investigate more in detail our previously proposed deprotonation and light-induced oxidation reactions composing the formation of the Ir-oxo complex. In particular, we discuss effects of light irradiation and WO3 support on the formation of the Ir-oxo complex. We suggest two distinct mechanisms, that is, direct and indirect for the light-induced oxidation. In the direct mechanism electrons are directly transferred from the occupied Ï∗ orbitals of IrIII-OH or IrIV=Oâ to the conduction band of the WO3 surface, whereas in the indirect mechanism electrons are first excited from the valence band to the conduction band of the WO3 surface due to the UV light, and then the resultant electron hole oxidizes the Ir complex. In the direct mechanism, in particular, we found that the lowest energy of the anode's conduction band determines the adsorption wavelength of the light irradiation, enabling us to predict alternative semiconductor anodes for more efficient formation of the Ir-oxo complex.

  • Temperature dependence of spherical electron transfer in a nanosized [Fe14] complex Reviewed International journal

    Wei Huang, Shuqi Wu, Xiangwei Gu, Yao Li, Atsushi Okazawa, Norimichi Kojima, Shinya Hayami, Michael L. Baker, Peter Bencok, Mariko Noguchi, Yuji Miyazaki, Motohiro Nakano, Takumi Nakanishi, Shinji Kanegawa, Yuji Inagaki, Tatsuya Kawae, Gui Lin Zhuang, Yoshihito Shiota, Kazunari Yoshizawa, Dayu WuOsamu Sato

    Nature communications   10 ( 1 )   5510   2019.12

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    The study of transition metal clusters exhibiting fast electron hopping or delocalization remains challenging, because intermetallic communications mediated through bridging ligands are normally weak. Herein, we report the synthesis of a nanosized complex, [Fe(Tp)(CN)3]8[Fe(H2O)(DMSO)]6 (abbreviated as [Fe14], Tp−, hydrotris(pyrazolyl)borate; DMSO, dimethyl sulfoxide), which has a fluctuating valence due to two mobile d-electrons in its atomic layer shell. The rate of electron transfer of [Fe14] complex demonstrates the Arrhenius-type temperature dependence in the nanosized spheric surface, wherein high-spin centers are ferromagnetically coupled, producing an S = 14 ground state. The electron-hopping rate at room temperature is faster than the time scale of Mössbauer measurements (<~10−8 s). Partial reduction of N-terminal high spin FeIII sites and electron mediation ability of CN ligands lead to the observation of both an extensive electron transfer and magnetic coupling properties in a precisely atomic layered shell structure of a nanosized [Fe14] complex.

    DOI: 10.1038/s41467-019-13279-y

  • Cupric-superoxide complex that induces a catalytic aldol reaction-type C–C bond formation Reviewed International journal

    Tsukasa Abe, Yuta Hori, Yoshihito Shiota, Takehiro Ohta, Yuma Morimoto, Hideki Sugimoto, Takashi Ogura, Kazunari Yoshizawa, Shinobu Itoh

    Communications Chemistry   2 ( 1 )   12   2019.12

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    Much recent attention has been focused on the structure and reactivity of transition-metal superoxide complexes, among which mononuclear copper(II)-superoxide complexes are recognized as key reactive intermediates in many biological and abiological dioxygen-activation processes. So far, several types of copper(II)-superoxide complexes have been developed and their electrophilic reactivity has been explored in C–H and O–H bond activation reactions. Here we demonstrate that a mononuclear copper(II)-(end-on)superoxide complex supported by a N-[(2-pyridyl)methyl]-1,5-diazacyclooctane tridentate ligand can induce catalytic C–C bond formation reaction between carbonyl compounds (substrate) and the solvent molecule (acetone), giving β-hydroxy-ketones (aldol). Kinetic and spectroscopic studies at low temperature as well as DFT calculation studies support a nucleophilic reactivity of the superoxide species toward the carbonyl compounds, providing new insights into the reactivity of transition-metal superoxide species not only in biological oxidation reactions but also in synthetic organic chemistry.

  • Giant anisotropic thermal expansion actuated by thermodynamically assisted reorientation of imidazoliums in a single crystal Reviewed International journal

    Zi Shuo Yao, Hanxi Guan, Yoshihito Shiota, Chun Ting He, Xiao Lei Wang, Shu Qi Wu, Xiaoyan Zheng, Sheng Qun Su, Kazunari Yoshizawa, Xueqian Kong, Osamu Sato, Jun Tao

    Nature communications   10 ( 1 )   4805   2019.12

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    Materials demonstrating unusual large positive and negative thermal expansion are fascinating for their potential applications as high-precision microscale actuators and thermal expansion compensators for normal solids. However, manipulating molecular motion to execute huge thermal expansion of materials remains a formidable challenge. Here, we report a single-crystal Cu(II) complex exhibiting giant thermal expansion actuated by collective reorientation of imidazoliums. The circular molecular cations, which are rotationally disordered at a high temperature and statically ordered at a low temperature, demonstrate significant reorientation in the molecular planes. Such atypical molecular motion, revealed by variable-temperature single crystal X-ray diffraction and solid-state NMR analyses, drives an exceptionally large positive thermal expansion and a negative thermal expansion in a perpendicular direction of the crystal. The consequent large shape change (~10%) of bulk material, with remarkable durability, suggests that this complex is a strong candidate as a microscale thermal actuating material.

    DOI: 10.1038/s41467-019-12833-y

  • Mechanistic Study on Ring-Contracting Skeletal Rearrangement from Porphycene to Isocorrole by Experimental and Theoretical Methods Reviewed International journal

    Taro Koide, Takafumi Maeda, Tsukasa Abe, Yoshihito Shiota, Yoshio Yano, Toshikazu Ono, Kazunari Yoshizawa, Yoshio Hisaeda

    European Journal of Organic Chemistry   2020 ( 12 )   1811 - 1816   2019.12

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    In this study, the ring contracting skeletal rearrangement reaction in one-pot under basic conditions from octaethylporphycene to two types of isocorroles, i.e., the meso-formyl and meso-free forms, was confirmed and the reaction mechanism was proposed by the comparative analyses of the experimental and theoretical studies. The electron accepting nature of the porphycene and imine-amine conversion of pyrrole rings make it possible to react with hydroxide ions and the following reaction to afford isocorroles. Based on this reaction, the valence of the compound as a ligand as well as the photochemical and electrochemical properties were dramatically changed.

    DOI: https://doi.org/10.1002/ejoc.201901659

  • Mechanistic insights into methane oxidation by molecular oxygen under photoirradiation: Controlled radical chain reactions Invited Reviewed International journal

    Yuta Hori, Tsukasa Abe, Yoshihito Shiota, Kazunari Yoshizawa

    Bulletin of the Chemical Society of Japan   92 ( 11 )   1840 - 1846   2019.11

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    The selective oxidation of CH4 using O2 is one of the most attractive subjects as an elusive target reaction. Ohkubo and Hirose recently reported that chlorine dioxide radical (ClO2•), which is generated by mixing NaClO2 and HCl in an aqueous solution, acts as an efficient oxidant in the oxidation of CH4 to CH3OH and HCOOH under photoirradiation in the two-phase system of perfluorohexane and water (Angew. Chem., Int. Ed. 2018, 57, 2126). The reaction system gives CH3OH and HCOOH without further oxidation products. They proposed that methoxy radical (CH3O•) plays an important role as an intermediate in the oxidation of CH4. In the present work, we focus on the reactivity of CH3O• to CH4 in detail to propose a reasonable radical mechanism for the oxidation of CH4 using DFT calculations at the M06-2X/6-311+G** level of theory and UCCSD(T)/6-311+G** calculations. Our reaction analysis suggests that the reaction of CH3O• with CH4 and the disproportionation of CH3O• take place as CH4 + CH3O• ¼ CH3• + CH3OH and 2CH3O• ¼ CH3OH + HCHO, respectively. In contrast, the isomerization from CH3O• to CH2•(OH), suggested by Ohkubo and Hirose, is unlikely to occur under ambient conditions, due to the high activation barrier for this reaction. A better understanding of the well-controlled radical chain reactions is useful for reaction design of the hydroxylation of methane.

    DOI: 10.1246/bcsj.20190171

  • An azulene-based chiral helicene and its air-stable cation radical Reviewed International journal

    Masahiro Narita, Takaaki Teraoka, Toshihiro Murafuji, Yoshihito Shiota, Kazunari Yoshizawa, Shigeki Mori, Hidemitsu Uno, Shinji Kanegawa, Osamu Sato, Kenta Goto, Fumito Tani

    Bulletin of the Chemical Society of Japan   92 ( 11 )   1867 - 1873   2019.11

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    A helicene compound called AIBTh, wherein two azulene units are fused with isobenzothiophene, has been prepared and characterized by spectroscopic and crystallographic methods. The enantiomers of AIBTh were resolved by HPLC, exhibiting stable optical activity. AIBTh showed two reversible oxidation and one irreversible reduction waves with a HOMO-LUMO gap of 2.07 eV. Upon one-electron oxidation of AIBTh, its air-stable cation radical was isolated and analyzed by EPR as well as X-ray crystallography. Based on the EPR spectrum, the crystal structure, and DFT calculation, it is suggested that favorable resonance structures including aromatic tropylium cation forms and wide delocalization of electronic spin are dominating in the electronic structure of the cation radical.

    DOI: 10.1246/bcsj.20190219

  • Role of Amino Acid Residues for Dioxygen Activation in the Second Coordination Sphere of the Dicopper Site of pMMO Reviewed International journal

    Mayuko Miyanishi, Tsukasa Abe, Yuta Hori, Yoshihito Shiota, Kazunari Yoshizawa

    JournalInorganic chemistry   58 ( 18 )   12280 - 12288   2019.9

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    Formation of an active oxygen species at the dicopper site of pMMO is studied by using density functional theory (DFT) calculations. The role of the amino acid residues of tyrosine (Tyr374) and glutamate (Glu35) located in the second coordination sphere of the dicopper site is discussed in detail. The phenolic proton of the tyrosine residue is transferred to the Cu2O2 core in a two-step manner via the glutamate residue, and an electron is directly transferred to the Cu2O2 core. These proton- and electron-transfer processes induce the O-O bond cleavage of the μ-ν2:ν2-peroxodicopper(II) species to form the (μ-oxo)(μ-hydroxo)CuIICuIII species, which is able to play a key role of methane hydroxylation at the dicopper site of pMMO (Inorg. Chem. 2013, 52, 7907). This proton-coupled electron-transfer mechanism is a little different from that in tyrosinase in that the proton of substrate tyrosine is directly transferred to the dicopper site (J. Am. Chem. Soc. 2006, 128, 9873) because there is no proton acceptor in the vicinity of the dicopper site of tyrosinase. The rate-determining step for the formation of the (μ-oxo)(μ-hydroxo)CuIICuIII species is determined to be the O-O bond cleavage. These results shed new light on the interpretation of the role of the tyrosine and glutamate residues located in the second coordination sphere of the dicopper site of pMMO.

    DOI: 10.1021/acs.inorgchem.9b01752

  • Local structures and electronic properties of In atoms in In-doped ZnO Reviewed International journal

    Yuta Hori, Yoshihito Shiota, Tomonori Ida, Kazunari Yoshizawa, Motohiro Mizuno

    Thin Solid Films   685   428 - 433   2019.9

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    Indium-doped zinc oxide (IZO) is an n-type semiconductor and an alternative to indium tin oxide, which is widely used in transparent electrodes. In order to design and prepare optical and electrical functional materials with IZO, it is important to understand the effects of indium (In) doping on zinc oxide (ZnO). In this study, the local structures and electronic properties of IZO were investigated by first-principle calculations. The formation energies of IZO with the substitution of an In atom in the place of a Zn atom were determined to be less than those of IZO with the intercalation of In atoms into interstitial sites in ZnO regardless of the amount of In atoms. From analyzing calculated band structures for the substitution and intercalation models, the relationship between the effect of In dopant and the conductivity of IZO is discussed.

  • Observation of Proton Transfer Coupled Spin Transition and Trapping of Photoinduced Metastable Proton Transfer State in an Fe(II) Complex Reviewed International journal

    Takumi Nakanishi, Yuta Hori, Hiroyasu Sato, Shu Qi Wu, Atsushi Okazawa, Norimichi Kojima, Takashi Yamamoto, Yasuaki Einaga, Shinya Hayami, Yusuke Horie, Hajime Okajima, Akira Sakamoto, Yoshihito Shiota, Kazunari Yoshizawa, Osamu Sato

    Journal of the American Chemical Society   141 ( 36 )   14384 - 14393   2019.9

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    An important technique to realize novel electron- A nd/or proton-based functionalities is to use a proton-electron coupling mechanism. When either a proton or electron is excited, the other one is modulated, producing synergistic functions. However, although compounds with proton-coupled electron transfer have been synthesized, crystalline molecular compounds that exhibit proton-transfer-coupled spin-transition (PCST) behavior have not been reported. Here, we report the first example of a PCST Fe(II) complex, wherein the proton lies on the N of hydrazone and pyridine moieties in the ligand at high-spin and low-spin Fe(II), respectively. When the Fe(II) complex is irradiated with light, intramolecular proton transfer occurs from pyridine to hydrazone in conjunction with the photoinduced spin transition via the PCST mechanism. Because the light-induced excited high-spin state is trapped at low temperatures in the Fe(II) complex- A phenomenon known as the light-induced excited-spin-state trapping effect-the light-induced proton-transfer state, wherein the proton lies on the N of hydrazone, is also trapped as a metastable state. The proton transfer was accomplished within 50 ps at 190 K. The bistable nature of the proton position, where the position can be switched by light irradiation, is useful for modulating proton-based functionalities in molecular devices.

    DOI: 10.1021/jacs.9b07204

  • Real-space observation of far- and near-field-induced photolysis of molecular oxygen on an Ag(110) surface by visible light Reviewed International journal

    Chenfang Lin, Kei Ikeda, Yoshihito Shiota, Kazunari Yoshizawa, Takashi Kumagai

    Journal of Chemical Physics   151 ( 14 )   144705   2019.8

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    Dissociation of molecular oxygen is an important elementary process in heterogeneous catalysis. Here, we report on a real-space observation of oxygen photolysis on the Ag(110) surface at 78 K by far- and near-field excitation in the ultraviolet-near-infrared range using a low-temperature scanning tunneling microscope (STM) combined with wavelength-tunable laser excitation. The photolysis of isolated oxygen molecules on the surface occurs even by visible light with the cross section of ∼10-19 cm2. Time-dependent density functional theory calculations reveal optical absorption of the hybridized O2-Ag(110) complex in the visible and the near-infrared range which is associated with the oxygen photolysis. We suggest that the photolysis mechanism involves a direct charge transfer process. We also demonstrate that the photolysis can be largely enhanced in plasmonic STM junctions, and the cross section is estimated to be ∼10-17 cm-2 in the visible and the near-infrared range, which appears to be an interesting feature of plasmon-induced reactions from the perspective of photochemical conversion with the aid of solar energy.

    DOI: 10.1063/1.5112158

  • Formation of a Ruthenium(V) - Imido Complex and the Reactivity in Substrate Oxidation in Water through the Nitrogen Non-Rebound Mechanism Reviewed International journal

    Tomoya Ishizuka, Taichi Kogawa, Misaki Makino, Yoshihito Shiota, Kazuaki Ohara, Hiroaki Kotani, Shunsuke Nozawa, Shin Ichi Adachi, Kentaro Yamaguchi, Kazunari Yoshizawa, Takahiko Kojima

    Inorganic chemistry   58 ( 19 )   12815 - 12824   2019.8

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    A RuII - NH3 complex, 2, was oxidized through a proton-coupled electron transfer (PCET) mechanism with a CeIV complex in water at pH 2.5 to generate a RuV=NH complex, 5. Complex 5 was characterized with various spectroscopies, and the spin state was determined by the Evans method to be S = 1/2. The reactivity of 5 in substrate C-H oxidation was scrutinized in acidic water, using water-soluble organic substrates such as sodium ethylbenzene-sulfonate (EBS), which gave the corresponding 1-phenylethanol derivative as the product. In the substrate oxidation, complex 5 was converted to the corresponding RuIII - NH3 complex, 3. The formation of 1-phenylethanol derivative from EBS and that of 3 indicate that complex 5 as the oxidant does not perform nitrogen-atom transfer, in sharp contrast to other high-valent metal-imido complexes reported so far. Oxidation of cyclobutanol by 5 afforded only cyclobutanone as the product, indicating that the substrate oxidation by 5 proceeds through a hydride-transfer mechanism. In the kinetic analysis on the C-H oxidation, we observed kinetic isotope effects (KIEs) on the C-H oxidation with use of deuterated substrates and remarkably large solvent KIE (sKIE) in D2O. These positive KIEs indicate that the rate-determining step involves not only cleavage of the C-H bond of the substrate but also proton transfer from water molecules to 5. The unique hydride-transfer mechanism in the substrate oxidation by 5 is probably derived from the fact that the RuIV - NH2 complex (4) formed from 5 by 1e-/1H+ reduction is unstable and quickly disproportionates into 3 and 5.

    DOI: 0.1021/acs.inorgchem.9b01781

  • Methane selective oxidation to methanol by metal-exchanged zeolites: A review of active sites and their reactivity Reviewed International journal

    Muhammad Haris Mahyuddin, Yoshihito Shiota, Kazunari Yoshizawa

    Catalysis Science and Technology   9 ( 8 )   1744 - 1768   2019.8

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    Over the past decade, zeolites (microporous aluminosilicate minerals) have been gaining significant popularity due to their broad applications in catalysis including the dream reaction of selective oxidation (hydroxylation) of methane to methanol at low temperature. In this review, we outline the current main challenges in the development of Fe-, Cu-, Co- and Ni-exchanged zeolites for methane hydroxylation and summarize key findings that have been reported in both spectroscopy and computational studies. Also, using density functional theory (DFT) calculations, we calculate energy diagrams of methane hydroxylation over various structures of metal-oxo active sites in zeolites and discuss some key points that can be improved for achieving higher reactivity. Short outlooks on the future research opportunities are also discussed.

    DOI: 10.1039/c8cy02414f

  • Iron complex of a quadruply fused porphyrin: Synthesis, structure and redox properties Reviewed International journal

    Tomoya Ishizuka, Keiyu Komamura, Yuta Saegusa, Shogo Tanaka, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    Journal of Porphyrins and Phthalocyanines   24 ( 01n03 )   1 - 7   2019.8

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    An iron(II) complex of a quadruply ring-fused porphyrin (QFP), Fe-1, in which four mesityl groups were introduced at the periphery to improve the solubility in organic solvents, has been newly synthesized and characterized. In the pyridine solution, two pyridine molecules bind to the low-spin Fe II center of Fe-1 as axial ligands to make the complex stable even under air. Characterization of Fe-1 was performed using ¹ H NMR spectroscopy, MALDI-TOF-MS spectrometry and single-crystal X-ray diffraction analysis. The ¹ H NMR signals of Fe-1 were observed in the diamagnetic region, reflecting the low-spin state of the Fe II center. In the differential pulse voltammogram of Fe-1, three oxidation waves and four reduction waves were observed in pyridine; the first oxidation wave at -0.08 V vs. Fc/Fc[Formula: see text] can be ascribed to the oxidation process of the Fe II center, Fe II /Fe III , and other six waves can be assigned to the redox processes of the QFP ligand. Furthermore, the ESR measurement of 1e[Formula: see text]-reduced Fe-1 upon controlled-potential bulk electrolysis in pyridine exhibited a signal at [Formula: see text] 2.003 with a well-resolved 45-line hyperfine splitting at room temperature, due to the coupling with four nitrogen nuclei and twelve hydrogen ones of the QFP ligand. This indicates that the ligand radical anion of Fe-1 is stabilized by delocalization of the spin density owing to the peripheral ring fusion and resultant expansion of the [Formula: see text]-conjugation.

    DOI: 10.1142/S1088424619500846

  • Dual Catalytic Cycle of H2 and H2O Oxidations by a Half-Sandwich Iridium Complex: A Theoretical Study Reviewed International journal

    Kei Ikeda, Yuta Hori, Muhammad Haris Mahyuddin, Yoshihito Shiota, Aleksandar Staykov, Takahiro Matsumoto, Kazunari Yoshizawa, Seiji Ogo

    Inorganic chemistry   58 ( 11 )   7274 - 7284   2019.1

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    While hydrogenase and photosystem II enzymes are known to oxidize H2 and H2O, respectively, a recently reported iridium aqua complex [IrIII(η5-C5Me5){bpy(COOH)2}(H2O)]2+ is able to oxidize both of the molecules and generate energies as in the fuel and solar cells (Ogo et al. ChemCatChem 2017, 9, 4024-4028). To understand the mechanism behind such an interesting bifunctional catalyst, in the present study, we perform density functional theory (DFT) calculations on the dual catalytic cycle of H2 and H2O oxidations by the iridium aqua complex. In the H2 oxidation, we found that the H-H bond is easily cleaved in a heterolytic fashion, and the resultant iridium hydride complex is significantly stabilized by the presence of H2O molecules, due to dihydrogen bond. The rate-determining step of this reaction is found to be the H2O → H2 ligand substitution with an activation energy of 10.7 kcal/mol. In the H2O oxidation, an iridium oxo complex originating from an oxidation of the iridium aqua complex forms a hydroperoxide complex, where an O-O bond is formed with an activation energy of 21.0 kcal/mol. Such a relatively low activation barrier is possible only when at least two H2O molecules are present in the reaction, allowing the water nucleophilic attack (WNA) mechanism to take place. The present study suggests and discusses in detail six reaction steps required for the dual catalytic cycle to complete.

    DOI: 10.1021/acs.inorgchem.9b00307

  • Fundamental electron-transfer and proton-coupled electron-transfer properties of Ru(iv)-oxo complexes Reviewed International journal

    Hiroaki Kotani, Hinatsu Shimomura, Momoka Horimoto, Tomoya Ishizuka, Yoshihito Shiota, Kazunari Yoshizawa, Sachiko Yanagisawa, Yuka Kawahara-Nakagawa, Minoru Kubo, Takahiko Kojima

    Dalton Transactions   48 ( 35 )   13154 - 13161   2019.1

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    Isolation and characterisation of RuIV(O) complexes were accomplished to investigate their fundamental electron transfer (ET) and proton-coupled ET (PCET) properties. Reorganisation energies (λ) in electron transfer (ET) and proton-coupled ET (PCET) from electron donors to the isolated RuIV(O) complexes have been determined for the first time to be in the range of 1.70-1.88 eV (ET) and 1.20-1.26 eV (PCET). It was suggested that the reduction of the λ values of PCET in comparison with those of ET should be due to the smaller structural change in PCET than that in ET on the basis of DFT calculations on 1 and 1e--reduced 1 in the absence and presence of TFA, respectively. In addition, the smaller λ values for the RuIV(O) complexes than those reported for FeIV(O) and MnIV(O) complexes should be due to the lack of participation of dσ orbitals in the ET and PCET reactions. This is the first example to evaluate fundamental ET and PCET properties of RuIV(O) complexes leading to further understanding of their reactivity in oxidation reactions.

  • High-temperature cooperative spin crossover transitions and single-crystal reflection spectra of [Fe III (qsal) 2 ](CH 3 OSO 3 ) and related compounds Reviewed International journal

    Kazuyuki Takahashi, Kaoru Yamamoto, Takashi Yamamoto, Yasuaki Einaga, Yoshihito Shiota, Kazunari Yoshizawa, Hatsumi Mori

    Crystals   9 ( 2 )   81   2019.1

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    New Fe(III) compounds from qsal ligand, [Fe(qsal) 2 ](CH 3 OSO 3 ) (1) and [Fe(qsal) 2 ](CH 3 SO 3 )·CH 3 OH (3), along with known compound, [Fe(qsal) 2 ](CF 3 SO 3 ) (2), were obtained as large well-shaped crystals (Hqsal = N-(8-quinolyl)salicylaldimine). The compounds 1 and 2 were in the low-spin (LS) state at 300 K and exhibited a cooperative spin crossover (SCO) transition with a thermal hysteresis loop at higher temperatures, whereas 3 was in the high-spin (HS) state below 300 K. The optical conductivity spectra for 1 and 3 were calculated from the single-crystal reflection spectra, which were, to the best of our knowledge, the first optical conductivity spectra of SCO compounds. The absorption bands for the LS and HS [Fe(qsal) 2 ] cations were assigned by time-dependent density functional theory calculations. The crystal structures of 1 and 2 consisted of a common one-dimensional (1D) array of the [Fe(qsal) 2 ] cation, whereas that of 3 had an unusual 1D arrangement by π-stacking interactions which has never been reported. The crystal structures in the high-temperature phases for 1 and 2 indicate that large structural changes were triggered by the motion of counter anions. The comparison of the crystal structures of the known [Fe(qsal) 2 ] compounds suggests the significant role of a large non-spherical counter-anion or solvate molecule for the total lattice energy gain in the crystal of a charged complex.

    DOI: 10.3390/cryst9020081

  • Redox behaviour of the β-dihydroporphycene cobalt complex: study on the effect of hydrogenation of the ligand Reviewed International journal

    Koichi Hashimoto, Taro Koide, Toru Okawara, Hisashi Shimakoshi, Yuta Hori, Yoshihito Shiota, Kazunari Yoshizawa, Yoshio Hisaeda

    Dalton Transactions   48 ( 3 )   872 - 881   2019.1

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    The dihydrogenated porphycene cobalt(ii) complex was synthesized and electrochemical experiments were carried out. The one-electron reduction of the complex proceeded at the central metal to afford the Co(i) species; in contrast, for the non-hydrogenated porphycene cobalt(ii) complex, the one-electron reduction gave the ligand reduced radical anion species. The reactivity of the one-electron reduced species with alkyl halides showed clear differences between the complexes. Hydrogenation of the β-position of the porphycene makes it possible to generate a central cobalt reduced species possessing a higher reactivity than the ligand reduced radical anion species.

    DOI: 10.1039/c8dt03743d

  • Visible light-driven cross-coupling reactions of alkyl halides with phenylacetylene derivatives for C(sp3)-C(sp) bond formation catalyzed by a B12 complex Reviewed International journal

    Li Chen, Yohei Kametani, Kenji Imamura, Tsukasa Abe, Yoshihito Shiota, Kazunari Yoshizawa, Yoshio Hisaeda, Hisashi Shimakoshi

    Chemical Communications   55 ( 87 )   13070 - 13073   2019.1

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    Visible light-driven cross-coupling reactions of alkyl halides with phenylacetylene and its derivatives catalyzed by the cobalamin derivative (B12) with the [Ir(dtbbpy)(ppy)2]PF6 photocatalyst at room temperature are reported. The robust B12 catalyst and Ir photocatalyst provided high turnover numbers of over 33 000 for the reactions.

    DOI: 10.1039/c9cc06185a

  • Importance of the Reactant-State Potentials of Chromium(V)-Oxo Complexes to Determine the Reactivity in Hydrogen-Atom Transfer Reactions Invited Reviewed International journal

    Hiroaki Kotani, Suzue Kaida, Tomoya Ishizuka, Kaoru Mieda, Miyuki Sakaguchi, Takashi Ogura, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    Inorganic chemistry   57 ( 21 )   13929 - 13936   2018.11

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    A new chromium(V)-oxo complex, [CrV(O)(6-COO--py-tacn)]2+ (1; 6-COO--py-tacn = 1-(6-carboxylato-2-pyridylmethyl)-4,7-dimethyl-1,4,7-triazacyclononane), was synthesized and characterized to evaluate the reactivity of CrV(O) complexes in a hydrogen-atom transfer (HAT) reaction by comparing it with that of a previously reported CrV(O) complex, [CrV(O)(6-COO--tpa)]2+ (2; 6-COO--tpa = N,N-bis(2-pyridylmethyl)-N-(6-carboxylato-2-pyridylmethyl)amine). Definitive differences of these two CrV(O) complexes were observed in resonance Raman scatterings of the Cr-O bond (ν = 911 cm-1 for 1 and 951 cm-1 for 2) and the reduction potential (0.73 V vs SCE for 1 and 1.23 V for 2); this difference should be derived from that of the ligand bound at the trans position to the oxo ligand, a tertiary amino group in 1, and a pyridine nitrogen in 2. When we employed 9,10-dihydroanthracene as a substrate, the second-order rate constant (k) of 1 was 4000 times smaller than that of 2. Plots of normalized k values for both complexes relative to bond dissociation energies (BDEs) of C-H bonds to be cleaved in several substrates showed a pair of parallel lines with slopes of -0.91 for 1 and -0.62 for 2, indicating that the HAT reactions by the two complexes proceed via almost the same transition states. Judging from estimated BDEs of CrIV(OH)/CrV(O) (85-87 kcal mol-1 for 1 and 92-94 kcal mol-1 for 2) and the activation barrier in the HAT reaction of DHA (Ea = 7.9 kcal mol-1 for 1 and Ea = 4.8 kcal mol-1 for 2), the reactivity of CrV(O) complexes in HAT reactions depends on the energy level of the reactant state rather than the product state.

    DOI: 10.1021/acs.inorgchem.8b02453

  • Importance of the Reactant-State Potentials of Chromium(V)-Oxo Complexes to Determine the Reactivity in Hydrogen-Atom Transfer Reactions Reviewed

    Kotani, Hiroaki, Kaida, Suzue, Ishizuka, Tomoya, Mieda, Kaoru, Sakaguchi, Miyuki, Ogura, Takashi, Shiota, Yoshihito, Yoshizawa, Kazunari, Kojima, Takahiko

    Inorganic Chemistry   57 ( 21 )   13929 - 13936   2018.11

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    Importance of the Reactant-State Potentials of Chromium(V)-Oxo Complexes to Determine the Reactivity in Hydrogen-Atom Transfer Reactions
    A new chromium(V)-oxo complex, [Cr(O)(6-COO-py-tacn)] (1; 6-COO-py-tacn = 1-(6-carboxylato-2-pyridylmethyl)-4,7-dimethyl-1,4,7-triazacyclononane), was synthesized and characterized to evaluate the reactivity of Cr(O) complexes in a hydrogen-atom transfer (HAT) reaction by comparing it with that of a previously reported Cr(O) complex, [Cr(O)(6-COO-tpa)] (2; 6-COO-tpa = N, N-bis(2-pyridylmethyl)- N-(6-carboxylato-2-pyridylmethyl)amine). Definitive differences of these two Cr(O) complexes were observed in resonance Raman scatterings of the Cr-O bond (ν = 911 cm for 1 and 951 cm for 2) and the reduction potential (0.73 V vs SCE for 1 and 1.23 V for 2); this difference should be derived from that of the ligand bound at the trans position to the oxo ligand, a tertiary amino group in 1, and a pyridine nitrogen in 2. When we employed 9,10-dihydroanthracene as a substrate, the second-order rate constant ( k) of 1 was 4000 times smaller than that of 2. Plots of normalized k values for both complexes relative to bond dissociation energies (BDEs) of C-H bonds to be cleaved in several substrates showed a pair of parallel lines with slopes of -0.91 for 1 and -0.62 for 2, indicating that the HAT

    DOI: 10.1021/acs.inorgchem.8b02453

  • Theoretical Overview of Methane Hydroxylation by Copper-Oxygen Species in Enzymatic and Zeolitic Catalysts Reviewed International journal

    M. Haris Mahyuddin, Yoshihito Shiota, Aleksandar Staykov, Kazunari Yoshizawa

    Accounts of Chemical Research   51 ( 10 )   2382 - 2390   2018.10

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    ConspectusAs fossil-based energy sources become more depleted and with renewable-energy technologies still in a very early stage of development, the utilization of highly abundant methane as a transitional solution for current energy demands is highly important despite difficulties in transport and storage. Technologies enabling the conversion of methane to liquid/condensable energy carriers that can be easily transported and integrated into the existing chemical infrastructures are therefore essential. Although there commercially exists a two-step gas-to-liquid process involving syngas production, a novel route of methane conversion that can circumvent the high-cost production of syngas should be developed. Among all of the conceptually possible methods for converting methane to methanol, methane hydroxylation (CH4 + 1/2O2 → CH3OH) at low temperature seems to be the most viable since it provides a direct route of conversion and allows a much lower operational cost. However, it is hampered by the fact that the complete oxidation to CO2 is thermodynamically more favored. To overcome this, an effective catalyst that is able to "mildly" oxidize methane and stabilize the resultant methyl radical toward methanol formation is required. Particulate methane monooxygenase (pMMO) and copper-exchanged zeolites are two catalysts known to hydroxylate methane into methanol at low temperature with high selectivity. Having been studied for more than 30 years, these copper-cored catalysts are still relevant topics of discussion since the actual structure of the active sites has not been agreed upon, and thus, the reaction mechanism and factors influencing their reactivity and productivity are yet to be understood. Density functional theory (DFT) has provided us with a powerful computational tool for accomplishing these tasks.This Account presents an overview of the recent progress in the computational elucidation of the catalytic mechanism of methane hydroxylation by mono-, di-, and trinuclear copper sites in pMMO and Cu-exchanged zeolites as well as its correlations to the influencing factors that must be controlled to achieve higher reactivity. First, we briefly introduce the catalytic mechanism of a bare CuO+ cation as the simplest copper-oxo system in methane hydroxylation. The system is then extended to the copper-oxo species in pMMO and zeolites, and the radical and nonradical mechanisms are examined. Investigations of the reactivities of mononuclear and dinuclear copper-oxo species in the pMMO active site suggest that the bis(μ-oxo)CuIICuIII, (μ-oxo)(μ-hydroxo)CuIICuIII, and CuIIIO species are important for the catalytic activity of pMMO. In the case of Cu-exchanged zeolites, as the mono(μ-oxo)CuIICuII and tris(μ-oxo)CuIICuIIICuIII active sites have been fully characterized in experiments, here we discuss the effects of zeolite structures on the geometry and reactivity of the active sites.

    DOI: 10.1021/acs.accounts.8b00236

  • Intermediate-Spin Iron(III) Complexes Having a Redox-Noninnocent Macrocyclic Tetraamido Ligand Reviewed International journal

    Takahiko Kojima, Fumiya Ogishima, Takahisa Nishibu, Hiroaki Kotani, Tomoya Ishizuka, Toshihiro Okajima, Shunsuke Nozawa, Yoshihito Shiota, Kazunari Yoshizawa, Hiroyoshi Ohtsu, Masaki Kawano, Takuya Shiga, Hiroki Oshio

    Inorganic chemistry   57 ( 16 )   9683 - 9695   2018.8

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    An iron(III) complex having a dibenzotetraethyltetraamido macrocyclic ligand (DTTM4-), (NEt4)2[FeIII(DTTM)Cl] (1), was synthesized and characterized by crystallographic, spectroscopic, and electrochemical methods. Complex 1 has a square-pyramidal structure in the S = 3/2 spin state. The complex exhibited two reversible redox waves at +0.36 and +0.68 V (vs SCE) in the cyclic voltammogram measured in CH2Cl2 at room temperature. The stepwise oxidation of 1 using chemical oxidants allowed us to observe clear and distinct spectral changes with distinct isosbestic points for each step, in which oxidation occurred at the phenylenediamido moiety rather than the iron center. One-electron oxidation of 1 by 1 equiv of [RuIII(bpy)3](ClO4)3 (bpy = 2,2′-bipyridine) in CH2Cl2 afforded square-pyramidal (NEt4)[Fe(DTTM)Cl] (2), which was in the S = 1 spin state involving a ligand radical and showed a slightly distorted square-pyramidal structure. Complex 2 showed an intervalence charge-transfer band at 900 nm, which was assigned on the basis of time-dependent density functional theory calculations, to indicate that the complex is in a class IIA mixed-valence ligand-radical regime with Hab = 884 cm-1. Two-electron oxidation of 1 by 2 equiv of [(4-Br-Ph)3N·+](SbCl6) in CH2Cl2 afforded two-electron-oxidized species of 1, [Fe(DTTM)Cl] (3), which was in the S = 1/2 spin state; complex 3 exhibited a distorted square-pyramidal structure. X-ray absorption near-edge structure spectra of 1-3 were measured in both CH3CN solutions and BN pellets to observe comparable rising-edge energies for the three complexes, and Mössbauer spectra of 1-3 showed almost identical isomer shifts and quadruple splitting parameters, indicating that the iron centers of the three complexes are intact to be in the intermediate-spin iron(III) state. Thus, in complexes 2 and 3, it is evident that antiferromagnetic coupling is operating between the unpaired electron(s) of the ligand radical(s) and those of the iron(III) center.

    DOI: 10.1021/acs.inorgchem.8b00037

  • Dioxygen Activation on Cu-MOR Zeolite: Theoretical Insights into the Formation of Cu2O and Cu3O3 Active Species Reviewed International journal

    M. Haris Mahyuddin, Takahiro Tanaka, Aleksandar Staykov, Yoshihito Shiota, Kazunari Yoshizawa

    Inorganic chemistry   57 ( 16 )   10146 - 10152   2018.7

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    The utilization of low-cost and abundant oxygen (O2) as an oxidant in the activation of copper-exchanged zeolites is highly important for the direct, selective oxidation of methane to methanol at low temperatures. While two motifs of active sites, i.e., the [Cu2(μ-O)]2+ and [Cu3(μ-O)3]2+, have been experimentally observed in mordenite (MOR) zeolite, the mechanisms of their formation from the reaction of Cu-MOR with O2 are still unclear. In this study, we performed density functional theory (DFT) calculations for O2 activation over 2[Cu2]2+-MOR and [Cu3O]2+-MOR zeolites. For the reaction on the dicopper species, we found two possible reaction routes: O-O bond cleavage leading to (1) formation of a [Cu2(μ-O)]2+ active species and a trans-μ-1,2-peroxo-Si2 species and (2) simultaneous formation of two [Cu2(μ-O)]2+ active species neighboring to each other. These routes are both exothermic but require completely different O-O bond activation energies. For the reaction on the tricopper species, we suggest a peroxo-Cu3O species as the intermediate structure with two transition states (TSs) involved in the reaction. The first TS where a significant rearrangement of the tricopper site occurs is found to be rate-determining, while the second TS where the peroxo bond is cleaved results in a smaller activation barrier. This reaction, in contrast to the dicopper case, is slightly endothermic. The present study provides theoretical insights that may help design of better Cu-exchanged zeolite catalysts for methane hydroxylation to methanol.

    DOI: 10.1021/acs.inorgchem.8b01329

  • A Cocatalyst that Stabilizes a Hydride Intermediate during Photocatalytic Hydrogen Evolution over a Rhodium-Doped TiO2 Nanosheet Reviewed International journal

    Shintaro Ida, Kenta Sato, Tetsuya Nagata, Hidehisa Hagiwara, Motonori Watanabe, Namhoon Kim, Yoshihito Shiota, Michio Koinuma, Sakae Takenaka, Takaaki Sakai, Elif Ertekin, Tatsumi Ishihara

    Angewandte Chemie - International Edition   57 ( 29 )   9073 - 9077   2018.7

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    The hydrogen evolution reaction using semiconductor photocatalysts has been significantly improved by cocatalyst loading. However, there are still many speculations regarding the actual role of the cocatalyst. Now a photocatalytic hydrogen evolution reaction pathway is reported on a cocatalyst site using TiO2 nanosheets doped with Rh at Ti sites as one-atom cocatalysts. A hydride species adsorbed on the one-atom Rh dopant cocatalyst site was confirmed experimentally as the intermediate state for hydrogen evolution, which was consistent with the results of density functional theory (DFT) calculations. In this system, the role of the cocatalyst in photocatalytic hydrogen evolution is related to the withdrawal of photo-excited electrons and stabilization of the hydride intermediate species; the presence of oxygen vacancies induced by Rh facilitate the withdrawal of electrons and stabilization of the hydride.

    DOI: 10.1002/anie.201803214

  • Two Discrete RuCp* (Cp*=Pentamethylcyclopentadienyl) Binding Modes of N-Confused Porphyrins: Peripheral π Complex and Sitting Atop Ruthenocenophane Complex by Skeletal Transformation Invited Reviewed International journal

    Takaaki Yamamoto, Koki Mitsuno, Shigeki Mori, Shuhei Itoyama, Yoshihito Shiota, Kazunari Yoshizawa, Masatoshi Ishida, Hiroyuki Furuta

    Chemistry - A European Journal   24 ( 26 )   6742 - 6746   2018.5

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    Complexation of a RuCp* cation with N-confused tetraarylporphyrins (NCPs) forms directly bound ruthenium(II) pentamethylcyclopentadienyl (Cp*) π-complex on a specific meso-aryl group (e.g., phenyl) neighboring peripheral imino nitrogen of NCPs in high yields. In contrast, in the case of NCPs bearing bulky meso-substituents (e.g., 3,5-di-tert-butylphenyl), new ruthenocenophane-like complex embedded on an N-confused calix[4]phyrin was formed through multiple C−H bond activation of methyl groups of Cp* ligand. The mechanistic insight into the formation of the ruthenocenophane was derived from DFT calculations.

    DOI: 10.1002/chem.201801237

  • Mechanistic Insights into Homogeneous Electrocatalytic and Photocatalytic Hydrogen Evolution Catalyzed by High-Spin Ni(II) Complexes with S2N2‑Type Tetradentate Ligands Reviewed

    Hong, Dachao, Tsukakoshi, Yuto, Kotani, Hiroaki, Ishizuka, Tomoya, Ohkubo, Kei, Shiota, Yoshihito, Yoshizawa, Kazunari, Fukuzumi, Shunichi, Kojima, Takahiko

    Inorganic Chemistry   57 ( 12 )   7180 - 7190   2018.5

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    Mechanistic Insights into Homogeneous Electrocatalytic and Photocatalytic Hydrogen Evolution Catalyzed by High-Spin Ni(II) Complexes with S2N2‑Type Tetradentate Ligands
    We report homogeneous electrocatalytic and photocatalytic H evolution using two Ni(II) complexes with SN-type tetradentate ligands bearing two different sizes of chelate rings as catalysts. A Ni(II) complex with a five-membered SCS-Ni chelate ring (1) exhibited higher activity than that with a six-membered SCS-Ni chelate ring (2) in both electrocatalytic and photocatalytic H evolution despite both complexes showing the same reduction potentials. A stepwise reduction of the Ni center from Ni(II) to Ni(0) was observed in the electrochemical measurements; the first reduction is a pure electron transfer reaction to form a Ni(I) complex as confirmed by electron spin resonance measurements, and the second is a 1e/1H proton-coupled electron transfer reaction to afford a putative Ni(II)-hydrido (Ni-H) species. We also clarified that Ni(II) complexes can act as homogeneous catalysts in the electrocatalytic H evolution, in which complex 1 exhibited higher reactivity than that of 2. In the photocatalytic system using [Ru(bpy)] as a photosensitizer and sodium ascorbate as a reductant, complex 1 with the five-membered chelate ring also showed higher catalytic activity than that of 2 with the si

    DOI: 10.1021/acs.inorgchem.8b00881

  • Cobalt-Carbon Bond Formation Reaction via Ligand Reduction of Porphycene-Cobalt(II) Complex and Its Noninnocent Reactivity Invited Reviewed International journal

    Taro Koide, Isao Aritome, Tatsuya Saeki, Yoshitsugu Morita, Yoshihito Shiota, Kazunari Yoshizawa, Hisashi Shimakoshi, Yoshio Hisaeda

    ACS Omega   3 ( 4 )   4027 - 4034   2018.4

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    The interesting redox properties and reactivity of metalloporphycene have been studied for decades; however, the detailed experimental investigation on the reactivity and reaction mechanism under inert condition combined with theoretical calculations had not been performed so far. In this study, the novel reactivity of the reduced form of the cobalt porphycene with alkyl halides to form cobalt-carbon (Co-C) bonds was revealed. Under electrochemical reductive conditions, not the central cobalt, but the ligand was reduced and reacted with alkyl halides to afford the cobalt-alkyl complexes under N2 atmosphere in a glovebox. The reaction mechanism was clarified by the combination of experimental and theoretical studies that the porphycene ligand works as a noninnocent ligand and allows the SN2-type Co-C bond formation. This result provides us the possibility of the reaction triggered by the reduction of ligand with macrocyclic π-conjugated system, not by the reduction of metal.

    DOI: 10.1021/acsomega.8b00239

  • Disilaruthena- and Ferracyclic Complexes Containing Isocyanide Ligands as Effective Catalysts for Hydrogenation of Unfunctionalized Sterically Hindered Alkenes Reviewed International journal

    Yusuke Sunada, Hajime Ogushi, Taiji Yamamoto, Shoko Uto, Mina Sawano, Atsushi Tahara, Hiromasa Tanaka, Yoshihito Shiota, Kazunari Yoshizawa, Hideo Nagashima

    Journal of the American Chemical Society   140 ( 11 )   4119 - 4134   2018.3

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    Disilaferra- and disilaruthenacyclic complexes containing mesityl isocyanide as a ligand, 3′ and 4′, were synthesized and characterized by spectroscopy and crystallography. Both 3′ and 4′ showed excellent catalytic activity for the hydrogenation of alkenes. Compared with iron and ruthenium carbonyl analogues, 1′ and 2′, the isocyanide complexes 3′ and 4′ were more robust under the hydrogenation conditions, and were still active even at higher temperatures (∼80 °C) under high hydrogen pressure (∼20 atm). The iron complex 3′ exhibited the highest catalytic activity toward hydrogenation of mono-, di-, tri-, and tetrasubstituted alkenes among currently reported iron catalysts. Ruthenium complex 4′ catalyzed hydrogenation under very mild conditions, such as room temperature and 1 atm of H2. The remarkably high catalytic activity of 4′ for hydrogenation of unfunctionalized tetrasubstituted alkenes was especially notable, because it was comparable to the activity of iridium complexes reported by Crabtree and Pfaltz, which are catalysts with the highest activity in the literature. DFT calculations suggested two plausible catalytic cycles, both of which involved activation of H2 assisted by the metal-silicon bond through σ-bond metathesis of late transition metals (oxidative hydrogen migration). The linear structure of M C≡N - C (ipso carbon of the mesityl group) played an essential role in the efficient hydrogenation of sterically hindered tetrasubstituted alkenes.

    DOI: 10.1021/jacs.8b00812

  • Contribution of Coulomb Interactions to a Two-Step Crystal Structure Phase Transformation Coupled with a Significant Change in Spin Crossover Behavior for a Series of Charged FeII Complexes from 2,6-Bis(2-methylthiazol-4-yl)pyridine Reviewed International journal

    Kazuyuki Takahashi, Mitsunobu Okai, Tomoyuki Mochida, Takahiro Sakurai, Hitoshi Ohta, Takashi Yamamoto, Yasuaki Einaga, Yoshihito Shiota, Kazunari Yoshizawa, Hisashi Konaka, Akito Sasaki

    Inorganic chemistry   57 ( 3 )   1277 - 1287   2018.2

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    A series of [FeII(L)2](BF4)2 compounds were structurally and physically characterized (L = 2,6-bis(2-methylthiazol-4-yl)pyridine). A crystal structure phase transformation from dihydrate compound 1 to anhydrous compound 3 through partially hydrated compounds 2 and 2′ upon dehydration was found. Compounds 1 and 3 exhibited a gradual spin crossover (SCO) conversion, whereas compounds 2 and 2′ demonstrated two-step and one-step abrupt SCO transitions, respectively. An X-ray single-crystal structural analysis revealed that one-dimensional and two-dimensional Fe cation networks linked by π stacking and sulfur-sulfur interactions were formed in 1 and 3, respectively. A thermodynamic analysis of the magnetic susceptibility for 1, 2′, and 3 suggests that the enthalpy differences may govern SCO transition behaviors in the polymorphic compounds 2′ and 3. A structural comparison between 1 and 3 indicates that the SCO behavior variations and crystal structure transformation in the present [FeII(L)2](BF4)2 compounds can be interpreted by the relationship between the lattice enthalpies mainly arising from Coulomb interactions between the Fe cations and BF4 anions as in typical ionic crystals.

    DOI: 10.1021/acs.inorgchem.7b02721

  • Formation and Isolation of a Four-Electron-Reduced Porphyrin Derivative by Reduction of a Stable 20π Isophlorin Reviewed International journal

    Wataru Suzuki, Hiroaki Kotani, Tomoya Ishizuka, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    Angewandte Chemie - International Edition   57 ( 7 )   1973 - 1977   2018.2

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    The two-electron reduction of a diprotonated dodecaphenylporphyrin derivative by Na2S2O4 gave a corresponding isophlorin (Iph) selectively. Formation of Iph was confirmed by spectroscopic measurements and the isolation of tetramethylated Iph. Further reduction of Iph proceeded to form an unprecedented four-electron-reduced porphyrin (IphH2), which was fully characterized by spectroscopic and X-ray crystallographic analysis. IphH2, with a unique conformation, could be oxidized to reproduce the starting porphyrin, resulting in a proton-coupled four-electron reversible redox system.

    DOI: 10.1002/anie.201711058

  • Methane Partial Oxidation over [Cu2(μ-O)]2+ and [Cu3(μ-O)3]2+ Active Species in Large-Pore Zeolites Reviewed International journal

    M. Haris Mahyuddin, Takahiro Tanaka, Yoshihito Shiota, Aleksandar Staykov, Kazunari Yoshizawa

    ACS Catalysis   8 ( 2 )   1500 - 1509   2018.2

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    Copper-containing large-pore zeolites, such as Cu-mordenite (Cu-MOR) and Cu-omega (Cu-MAZ), oxidize methane to yield a high amount of methanol. Two distinct active centers in MOR zeolite, namely, [Cu2(μ-O)]2+ and [Cu3(μ-O)3]2+, have been proposed and debated. In particular, the [Cu2(μ-O)]2+ species was experimentally found to be formed on two different Al pair sites with different reactivities toward methane. However, computational attempts based on density functional theory (DFT) have not been able to confirm them. Moreover, the full cycle of the reaction, which includes methane activation, water-assisted methanol desorption, and a second methane reaction with the active species, has not been well understood yet. In this study, we employed DFT calculations based on the Perdew, Burke, and Ernzerhof functional to reasonably calculate all activation energies involved in such a complete reaction over periodic systems of [Cux(μ-O)y]2+-MOR and -MAZ (x, y = 2, 1 and 3, 3) in the high-spin and low-spin states. We found two Al pair sites in MOR zeolite that form two distinct [Cu2(μ-O)]2+ structures able to cleave the C-H bond of methane with activation energies excellently comparable with the experimental values. Our computational results further suggest that the addition of a water molecule helps the reaction to reduce the high methanol desorption energies. We also show that two of the three bridging O atoms in [Cu3(μ-O)3]2+-MOR and -MAZ significantly differ in reactivity toward methane.

    DOI: 10.1021/acscatal.7b03389

  • Trithiazolyl-1,3,5-triazines bearing decyloxybenzene moieties: Synthesis, photophysical and electrochemical properties, and self-assembly behavior Invited Reviewed International journal

    Shin Ichiro Kato, Satoshi Jin, Terutaka Kimura, Naoki Yoshikawa, Daiki Nara, Kenji Imamura, Yoshihito Shiota, Kazunari Yoshizawa, Ryo Katoono, Takeshi Yamanobe, Hiroki Uehara, Yosuke Nakamura

    Organic and Biomolecular Chemistry   16 ( 19 )   3584 - 3595   2018.1

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    We report the synthesis, photophysical properties, redox characteristics, and self-assembly behavior of disk-shaped trithiazolyl-1,3,5-triazines that bear decyloxybenzene moieties. These compounds were synthesized by a Migita-Kosugi-Stille coupling reaction of 1,3,5-trichlorotriazine with three different tributyltin(thiazoles) as the key step. The structure-property relationships, namely the effects of the incorporation of thiazole units into the triazine unit, the conjugation connectivity between the thiazole and triazine units, and the insertion of ethynylene spacers between the thiazole and decyloxybenzene moieties on the properties of the trithiazolyl-1,3,5-triazines were comprehensively investigated. Binding of the triazine core at the 5-position of the thiazole moieties effectively extended the π-conjugation and afforded high fluorescence quantum yields. The ethynylene spacers substantially lowered the LUMO level relative to the HOMO level. The prepared trithiazolyl-1,3,5-triazines self-assembled in solution, and the introduction of thiazole units at the 5-position enhanced this behavior. Detailed thermodynamic studies on the self-association behavior were conducted, and the formation of self-assembled 1D clusters is disclosed.

    DOI: 10.1039/c8ob00471d

  • Catalytic Performance of a Dicopper-Oxo Complex for Methane Hydroxylation Reviewed International journal

    Yuta Hori, Yoshihito Shiota, Tomokazu Tsuji, Masahito Kodera, Kazunari Yoshizawa

    Inorganic chemistry   57 ( 1 )   8 - 11   2018.1

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    A dicopper(II) complex, [Cu2(μ-OH)(6-hpa)]3+, where 6-hpa is 1,2-bis[2-[bis(2-pyridylmethyl)aminomethyl]-6-pyridyl]ethane, generates an oxyl radical of CuIIO• and catalyzes the selective hydroxylation of benzene to phenol. From the structural similarity to methane activation catalysts (e.g., bare CuO+ ion, Cu-ZSM-5, and particulate methane monooxygenase), it is expected to catalyze methane hydroxylation. The catalytic performance for the hydroxylation of methane to methanol by this dicopper complex is investigated by using density functional theory (DFT) calculations. The whole reaction of the methane conversion involves two steps without radical species: (1) C-H bond dissociation of methane by the CuIIO• moiety and (2) C-O bond formation with methyl migration. In the first step, the activation barrier is calculated to be 10.2 kcal/mol, which is low enough for reactions taking place under normal conditions. The activation barrier by the other CuIIO2• moiety is higher than that by the CuIIO• moiety, which should work to turn the next catalytic cycle. DFT calculations show that the dicopper complex has a precondition to hydroxylate methane to methanol. Experimental verification is required to look in detail at the reactivity of this dicopper complex.

    DOI: 10.1021/acs.inorgchem.7b02563

  • Ground-State Copper(III) Stabilized by N-Confused/N-Linked Corroles: Synthesis, Characterization, and Redox Reactivity Invited Reviewed International journal

    Yogesh Kumar Maurya, Katsuya Noda, Kazuhisa Yamasumi, Shigeki Mori, Tomoki Uchiyama, Kazutaka Kamitani, Tomoyasu Hirai, Kakeru Ninomiya, Maiko Nishibori, Yuta Hori, Yoshihito Shiota, Kazunari Yoshizawa, Masatoshi Ishida, Hiroyuki Furuta

    Journal of the American Chemical Society   140 ( 22 )   6883 - 6892   2018.1

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    Stable square planar organocopper(III) complexes (CuNCC2, CuNCC4, and CuBN) supported by carbacorrole-based tetradentate macrocyclic ligands with NNNC coordination cores were synthesized, and their structures were elucidated by spectroscopic means including X-ray crystallographic analysis. On the basis of their distinct planar structures, X-ray absorption/photoelectron spectroscopic features, and temperature-independent diamagnetic nature, these organocopper complexes can be preferably considered as novel organocopper(III) species. The remarkable stability of the high-valent Cu(III) states of the complexes stems from the closed-shell electronic structure derived from the peculiar NNNC coordination of the corrole-modified frameworks, which contrasts with the redox-noninnocent radical nature of regular corrole copper(II) complexes with an NNNN core. The proposed structure was supported by DFT (B3LYP) calculations. Furthermore, a π-laminated dimer architecture linked through the inner carbons was obtained from the one-electron oxidation of CuNCC4. We envisage that the precise manipulation of the molecular orbital energies and redox profiles of these organometallic corrole complexes could eventually lead to the isolation of yet unexplored high-valent metal species and the development of their organometallic reactions.

    DOI: 10.1021/jacs.8b01876

  • NH Tautomerism of a Quadruply Fused Porphyrin: Rigid Fused Structure Delays the Proton Transfer Reviewed International journal

    Yuta Saegusa, Tomoya Ishizuka, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    Journal of Physical Chemistry B   122 ( 1 )   316 - 327   2018.1

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    We report herein NH tautomerism of a freebase derivative of a quadruply fused porphyrin (H2QFP-Mes, 3), which has one mesityl group at one of the β-positions of the nonfused pyrroles to lower the structural symmetry, allowing us to observe the NH tautomerism with 1H NMR spectroscopy. Compound 3 was revealed to have the two inner NH protons on the two nonfused pyrroles, and the NH tautomerism of 3 was evidenced by variable-temperature (VT) 1H NMR experiments in various deuterated solvents. The VT-NMR studies revealed that the activation barrier for the NH tautomerism of 3 was larger than that of tetraphenylporphyrin. The positive activation entropy (ΔS‡ = 89 J mol-1 K-1), determined for the NH tautomerism, can be explained by dissociation of the π-π stacked dimer structure of 3 in the ground state, as evidenced by the crystal structure and NMR measurements. On the basis of the kinetic studies and density functional theory calculations, the stability of intermediates in the NH tautomerism of 3 and the transition states have been discussed in detail.

    DOI: 10.1021/acs.jpcb.7b10945

  • Efficient 1H NMR chiral discrimination of sulfoxides caused by the dynamic nature of (R,R)-3′,3″-biBINOL Reviewed International journal

    Toshio Kawanami, Kentaro Ishizuka, Hiroshi Furuno, Yoshihito Shiota, Kazunari Yoshizawa, Junji Inanaga

    Tetrahedron Asymmetry   28 ( 11 )   1587 - 1590   2017.11

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    A chiral BINOL dimer, (R,R)-3′,3″-BiBINOL, which possesses both rigid (atropos) and dynamic (tropos) axial chiralities, was found to work as an effective NMR chiral solvating reagent for the determination of the enantiomeric purities of various chiral sulfoxides. The unique chiral discrimination mechanism was also revealed by using DFT calculations and X-ray crystallographic analysis.

    DOI: 10.1016/j.tetasy.2017.10.008

  • Photochemical Intramolecular C−H Addition of Dimesityl(hetero)arylboranes through a [1,6]-Sigmatropic Rearrangement Reviewed International journal

    Naoki Ando, Aiko Fukazawa, Tomokatsu Kushida, Yoshihito Shiota, Shuhei Itoyama, Kazunari Yoshizawa, Yasunori Matsui, Yutaro Kuramoto, Hiroshi Ikeda, Shigehiro Yamaguchi

    Angewandte Chemie - International Edition   56 ( 40 )   12210 - 12214   2017.9

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    A new reaction mode for triarylboranes under photochemical conditions was discovered. Photoirradiation of dimesitylboryl-substituted (hetero)arenes produced spirocyclic boraindanes, where one of the C−H bonds in the ortho-methyl groups of the mesityl substituents was formally added in a syn fashion to a C−C double bond of the (hetero)aryl group. Quantum chemical calculations and laser flash photolysis measurements indicated that the reaction proceeds through a [1,6]-sigmatropic rearrangement. This behavior is reminiscent of the photochemical reaction mode of arylalkenylketones, thus demonstrating the isosteric relation between tricoordinate organoboron compounds and the corresponding pseudo-carbocationic species in terms of pericyclic reactions. Despite the disrupted π-conjugation, the resulting spirocyclic boraindanes exhibited a characteristic absorption band at relatively long wavelengths (λ=370—400 nm).

    DOI: 10.1002/anie.201706929

  • Theoretical Investigation of Methane Hydroxylation over Isoelectronic [FeO]2+- and [MnO]+-Exchanged Zeolites Activated by N2O Reviewed International journal

    M. Haris Mahyuddin, Yoshihito Shiota, Aleksandar Staykov, Kazunari Yoshizawa

    Inorganic chemistry   56 ( 17 )   10370 - 10380   2017.9

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    While the most likely structure of the active site in iron-containing zeolites has been recently identified as [FeO]2+ (Snyder et al. Nature 2016, 536, 317-321), the mechanism for the direct conversion of methane to methanol over this active species is still debatable between the direct-radical-rebound or nonradical (concerted) mechanism. Using density functional theory on periodic systems, we calculated the two reaction mechanisms over two d4 isoelectronic systems, [FeO]2+ and [MnO]+ zeolites. We found that [FeO]2+ zeolites favor the direct-radical-rebound mechanism with low CH4 activation energies, while [MnO]+ zeolites prefer the nonradical mechanism with higher CH4 activation energies. These contrasts, despite their isoelectronic structures, are mainly due to the differences in the metal coordination number and Oα (oxo) spin density. Moreover, molecular orbital analyses suggest that the zeolite steric hindrance further degrades the reactivity of [MnO]+ zeolites toward methane. Two types of zeolite frameworks, i.e., medium-pore ZSM-5 (MFI framework) and small-pore SSZ-39 (AEI framework) zeolites, were evaluated, but no significant differences in the reactivity were found. The rate-determining reaction step is found to be methanol desorption instead of methane activation. Careful examination of the most stable sites hosting the active species and calculation for N2O decomposition over [Fe]2+-MFI and -AEI zeolites were also performed.

    DOI: 10.1021/acs.inorgchem.7b01284

  • An Azulene-Fused Tetracene Diimide with a Small HOMO–LUMO Gap Reviewed International journal

    Taro Koide, Moritaka Takesue, Toshihiro Murafuji, Koichiro Satomi, Yasutaka Suzuki, Jun Kawamata, Kengo Terai, Mitsuharu Suzuki, Hiroko Yamada, Yoshihito Shiota, Kazunari Yoshizawa, Fumito Tani

    ChemPlusChem   82 ( 7 )   1010 - 1014   2017.8

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    A newly prepared tetraazulene-fused tetracene diimide (TA-fused TDI) showed absorption in the near-IR region owing to the effective extension of the π-conjugated system as well as a large two-photon absorption cross-section (σ(2)=2140 GM) at 950 nm. Four reversible reduction processes and n-type semiconductivity were also confirmed as attractive electronic properties of this compound.

    DOI: 10.1002/cplu.201600356

  • σ-CAM mechanisms for the hydrogenation of alkenes by cis- and trans- disilametallacyclic carbonyl complexes (M = Fe, Ru, Os): Experimental and theoretical studies Invited Reviewed International journal

    Konoka Hoshi, Atsushi Tahara, Yusuke Sunada, Hironori Tsutsumi, Ryoko Inoue, Hiromasa Tanaka, Yoshihito Shiota, Kazunari Yoshizawa, Hideo Nagashima

    Bulletin of the Chemical Society of Japan   90 ( 5 )   613 - 626   2017.5

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    The hydrogenation of alkenes catalyzed by disilametallacyclic carbonyl complexes of iron, ruthenium or osmium was studied experimentally and theoretically. The disilaruthenacycle 2 with two CO ligands in the trans-configuration was prepared, characterized, and its ability to catalyze hydrogenation was studied. Similar to the corresponding iron analogue 1 in which the CO ligands are in the cis-configuration, 2 contains a H2MSi4 core with SiHSi SISHA (secondary interaction of silicon and hydrogen atoms) and catalyzed the hydrogenation of several alkenes under mild conditions. DFT calculations of 1 and 2 with cis- and trans-CO configurations (cis-1, trans-1, cis-2 and trans-2) revealed that the mechanism of ethylene hydrogenation comprises three catalytic cycles, and a key step involves the H-H bond of H2 being activated by an M-Si bond through oxidative hydrogen migration. These mechanisms are a variety of α-CAM (complex-assisted metathesis) mechanisms. Further calculations suggest that these catalytic cycles can apply to the catalytic hydrogenation of ethylene by osmium analogues of 1 and 2 (cis-3 and trans-3). Some of the elementary reactions in the cycles are dependent on the metal, and the osmium complexes show different performance from the iron and ruthenium analogues due to the characteristic natures of the third-row transition metals.

    DOI: 10.1246/bcsj.20170004

  • Synergy of electrostatic and van der waals interactions in the adhesion of epoxy resin with carbon-fiber and glass surfaces Reviewed International journal

    Kazunari Yoshizawa, Takayuki Semoto, Seiji Hitaoka, Chisa Higuchi, Yoshihito Shiota, Hiromasa Tanaka

    Bulletin of the Chemical Society of Japan   90 ( 5 )   500 - 505   2017.5

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    The adhesion between epoxy resin and carbon fiber is investigated by using pair interaction energy decomposition analysis (PIEDA), by which the adhesive interaction energy and adhesive force can be partitioned into the electrostatic, exchangerepulsion, charge-transfer, and van der Waals (dispersion) contributions. The three stabilizing electrostatic, charge-transfer, and dispersion effects are correlated with the destabilizing exchange-repulsion effect. The surface structures of carbon fiber are modeled by the basal face, the armchair-edge structure, and the OH-functionalized armchair-edge structure of graphite. The surface of ?-cristobalite (covered with OH groups), which can be viewed as a good model of a hydrophilic glass surface, is also studied. Adhesive properties of the model interfaces are evaluated on the basis of the binding energy of the resin with the carbon and glass surfaces and the adhesive force acting at the interfaces in terms of energy decomposition. PIEDA calculations demonstrate that only dispersion interactions can substantially work in the hydrophobic surfaces of the basal face and armchair-edge structures. This is a direct consequence of the electrostatic and charge-transfer interactions being cancelled by the exchange-repulsion interactions. On the other hand, both electrostatic and dispersion interactions are significant in the OH-functionalized surfaces of the armchair edge of graphite and ?-cristobalite.

    DOI: 10.1246/bcsj.20160426

  • Catalytic C-H amination driven by intramolecular ligand-to-nitrene one-electron transfer through a rhodium(III) centre (vol 53, pg 4849, 2017) Reviewed

    Daiki Fujita, Hideki Sugimoto, Yoshihito Shiota, Yuma Morimoto, Kazunari Yoshizawa, Shinobu Itoh

    CHEMICAL COMMUNICATIONS   53 ( 41 )   5669 - 5669   2017.5

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    DOI: 10.1039/c7cc90176c

  • Formation of supramolecular hetero-triads by controlling the hydrogen bonding of conjugate bases with a diprotonated porphyrin based on electrostatic interaction Reviewed

    Suzuki, Wataru, Kotani, Hiroaki, Ishizuka, Tomoya, Shiota, Yoshihito, Yoshizawa, Kazunari, Kojima, Takahiko

    Chemical Communications   53 ( 47 )   6359 - 6362   2017.5

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    Formation of supramolecular hetero-triads by controlling the hydrogen bonding of conjugate bases with a diprotonated porphyrin based on electrostatic interaction
    The thermodynamic stability of diprotonated saddle-distorted dodecaphenylporphyrin (H4DPP(2+)(X(-))2) was controlled by the hydrogen-bonding strength of conjugate bases (X(-)) of strong acids (HX) or acids (R(+)-COOH) having positively charged moieties. The thermodynamic control of H4DPP(2+)(X(-))2 made it possible to achieve selective formation of supramolecular hetero-triads, H4DPP(2+)(X(-))(Cl(-)).

    DOI: 10.1039/C7CC03635C

  • Thermodynamics and Photodynamics of a Monoprotonated Porphyrin Directly Stabilized by Hydrogen Bonding with Polar Protic Solvents Reviewed International journal

    Wataru Suzuki, Hiroaki Kotani, Tomoya Ishizuka, Kei Ohkubo, Yoshihito Shiota, Kazunari Yoshizawa, Shunichi Fukuzumi, Takahiko Kojima

    Chemistry - A European Journal   23 ( 19 )   4669 - 4679   2017.4

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    Addition of 1 equiv of TFA to an acetone solution containing dodecaphenylporphyrin (H2DPP) in the presence of 10 % MeOH (v/v) resulted in selective formation of a monoprotonated form (H3DPP+), in sharp contrast to protonation of H2DPP directly affording a diprotonated form (H4DPP2+) in acetone in the absence of MeOH. The crucial role of MeOH for selective H3DPP+ formation was interpreted as hydrogen-bonding stabilization of H3DPP+, since a MeOH molecule was found to form hydrogen bonds with an NH proton of H3DPP+ in the crystal. The selectivity of H3DPP+ formation was evaluated by the formation yield of H3DPP+, which increased when elevating the portion of MeOH (0–10 %) in acetone with saturation behavior, suggesting that H3DPP+ is stabilized by hydrogen bonding with MeOH even in solution, together with the thermodynamic parameters determined from a van't Hoff plot based on the spectroscopic titration. Femto- and nanosecond laser flash photolysis allowed us to elucidate the photodynamics of H3DPP+ in intermolecular photoinduced electron transfer (ET) from ferrocene derivatives as one-electron donors to the triplet excited state of H3DPP+ as an electron acceptor. The second-order rate constants of the ET reactions were evaluated in light of the Marcus theory of ET. The reorganization energy of ET was determined to be 1.87 eV, which is slightly larger than that of H4DPP2+ in acetonitrile (1.69 eV), due to larger structural change upon ET than that of H4DPP2+.

    DOI: 10.1002/chem.201606012

  • Specific Enhancement of Catalytic Activity by a Dicopper Core: Selective Hydroxylation of Benzene to Phenol with Hydrogen Peroxide Reviewed International journal

    Tomokazu Tsuji, Antonius Andre Zaoputra, Yutaka Hitomi, Kaoru Mieda, Takashi Ogura, Yoshihito Shiota, Kazunari Yoshizawa, Hiroyasu Sato, Masahito Kodera

    Angewandte Chemie - International Edition   56 ( 27 )   7779 - 7782   2017.1

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    A dicopper(II) complex, stabilized by the bis(tpa) ligand 1,2-bis[2-[bis(2-pyridylmethyl)aminomethyl]-6-pyridyl]ethane (6-hpa), [Cu2(μ-OH)(6-hpa)]3+, was synthesized and structurally characterized. This complex catalyzed selective hydroxylation of benzene to phenol using H2O2, thus attaining large turnover numbers (TONs) and high H2O2 efficiency. The TON after 40 hours for the phenol production exceeded 12000 in MeCN at 50 °C under N2, the highest value reported for benzene hydroxylation with H2O2 catalyzed by homogeneous complexes. At 22 % benzene conversion, phenol (95.2 %) and p-benzoquinone (4.8 %) were produced. The mechanism of H2O2 activation and benzene hydroxylation is proposed.

    DOI: 10.1002/anie.201702291

  • Acid-Base Properties of a Freebase Form of a Quadruply Ring-Fused Porphyrin - Stepwise Protonation Induced by Rigid Ring-Fused Structure Reviewed International journal

    Yuta Saegusa, Tomoya Ishizuka, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    Journal of Organic Chemistry   82 ( 1 )   322 - 330   2017.1

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    We report herein unique stepwise protonation at inner imino-nitrogen atoms of a freebase derivative of a quadruply fused porphyrin (H2QFP), which has been newly synthesized. H2QFP has been revealed to have the two inner NH protons on the two nonfused pyrroles by X-ray diffraction analysis and 1H NMR spectroscopy. The first protonation at one of the two imino-nitrogen atoms of the fused pyrroles smoothly proceeds with trifluoroacetic acid (TFA) in CH2Cl2 and the equilibrium constant (K1) of the protonation has been determined to be (1.3 ± 0.1) × 105 M-1. In contrast, the second protonation at the other imino-nitrogen atom is hard to occur unless a large excess amount of TFA is used, as reflected on a much smaller equilibrium constant, K2 = 7.3 ± 0.3 M-1. The stepwise protonation is ascribed to the structural rigidity caused by the ring fusion and the resultant steric repulsion among inner NH atoms of the diprotonated form. Electrochemical studies have revealed that protonation at the pyrrole nitrogen atoms caused positive shifts of the reduction potentials of the QFP derivatives. In addition, the ESR spectrum of the electrochemically one-electron-reduced monoprotonated QFP derivative showed well-resolved hyperfine splitting to represent its unsymmetrical electronic structure due to the monoprotonation.

    DOI: 10.1021/acs.joc.6b02419

  • Anisotropic Change in the Magnetic Susceptibility of a Dynamic Single Crystal of a Cobalt(II) Complex Reviewed International journal

    Zi Shuo Yao, Shu Qi Wu, Yasutaka Kitagawa, Sheng Qun Su, You Gui Huang, Guo Ling Li, Zhong Hai Ni, Hiroyuki Nojiri, Yoshihito Shiota, Kazunari Yoshizawa, Soonchul Kang, Shinji Kanegawa, Osamu Sato

    Angewandte Chemie - International Edition   56 ( 3 )   717 - 721   2017.1

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    Atypically anisotropic and large changes in magnetic susceptibility, along with a change in crystalline shape, were observed in a CoIIcomplex at near room temperature. This was achieved by combining oxalate molecules, acting as rotor, and a CoIIion with unquenched orbital angular momentum. A thermally controlled 90° rotation of the oxalate counter anion triggered a symmetry-breaking ferroelastic phase transition, accompanied by contraction–expansion behavior (ca. 4.5 %) along the long axis of a rod-like single crystal. The molecular rotation induced a minute variation in the coordination geometry around the CoIIion, resulting in an abrupt decrease and a remarkable increase in magnetic susceptibility along the direction perpendicular and parallel to the long axis of the crystal, respectively. Theoretical calculations suggested that such an unusual anisotropic change in magnetic susceptibility was due to a substantial reorientation of magnetic anisotropy induced by slight disruption in the ideal D3coordination environment of the complex cation.

    DOI: 10.1002/anie.201606165

  • Catalytic C-H amination driven by intramolecular ligand-to-nitrene one-electron transfer through a rhodium(III) centre Reviewed International journal

    Daiki Fujita, Hideki Sugimoto, Yoshihito Shiota, Yuma Morimoto, Kazunari Yoshizawa, Shinobu Itoh

    Chemical Communications   53 ( 35 )   4849 - 4852   2017.1

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    Werner type six-coordinate rhodium(iii) complexes coordinated by a planar trianionic ligand and two axial aniline ligands are synthesised. The trianionic ligand behaves as a redox-active ligand to form a ligand radical species upon one-electron oxidation of the complex. The rhodium(iii) complexes catalyse C-H amination of external substrates such as xanthene with tosylazide as the nitrene source. DFT-calculation and kinetic deuterium isotope effects indicate that a di-radical rhodium(iii) complex formed by one-electron transfer from the redox-active ligand to the nitrene group works as a reactive intermediate to induce aliphatic C-H activation.

    DOI: 10.1039/c7cc01840a

  • Formation of supramolecular hetero-triads by controlling the hydrogen bonding of conjugate bases with a diprotonated porphyrin based on electrostatic interaction Reviewed International journal

    Wataru Suzuki, Hiroaki Kotani, Tomoya Ishizuka, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    Chemical Communications   53 ( 47 )   6359 - 6362   2017.1

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    The thermodynamic stability of diprotonated saddle-distorted dodecaphenylporphyrin (H4DPP2+(X-)2) was controlled by the hydrogen-bonding strength of conjugate bases (X-) of strong acids (HX) or acids (R+-COOH) having positively charged moieties. The thermodynamic control of H4DPP2+(X-)2 made it possible to achieve selective formation of supramolecular hetero-triads, H4DPP2+(X-)(Cl-).

    DOI: 0.1039/c7cc03635c

  • Isolation and phototransformation of enantiomerically pure iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C2]picolinate Invited Reviewed International journal

    Yue Wang, Takunori Harada, Yoshihito Shiota, Kazunari Yoshizawa, Heng Wang, Sheng Wang, Xichong Ye, Masamichi Ogasawara, Tamaki Nakano

    RSC Advances   7 ( 47 )   29550 - 29553   2017.1

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    Here we report the resolution of phosphorescent light-emitting iridium(iii) bis[(4,6-difluorophenyl)pyridinato-N,C2]-picolinate into its respective enantiomers by using chiral HPLC and the photo-induced transformation of the isolated enantiomers.

    DOI: 10.1039/c7ra04141a

  • Photocatalytic alkene reduction by a B12-TiO2 hybrid catalyst coupled with C-F bond cleavage for: Gem -difluoroolefin synthesis Reviewed International journal

    Hui Tian, Hisashi Shimakoshi, Kenji Imamura, Yoshihito Shiota, Kazunari Yoshizawa, Yoshio Hisaeda

    Chemical Communications   53 ( 68 )   9478 - 9481   2017.1

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    Photocatalytic syntheses of gem-difluoroolefins were performed using the B12-TiO2 hybrid catalyst during the CC bond reduction of α-trifluoromethyl styrenes with C-F bond cleavage at room temperature under nitrogen. The gem-difluoroolefins were used as synthetic precursors for fluorinated cyclopropanes.

    DOI: 10.1039/c7cc04377e

  • Roles of Zeolite Confinement and Cu-O-Cu Angle on the Direct Conversion of Methane to Methanol by [Cu2(μ-O)]2+-Exchanged AEI, CHA, AFX, and MFI Zeolites Reviewed International journal

    M. Haris Mahyuddin, Aleksandar Staykov, Yoshihito Shiota, Mayuko Miyanishi, Kazunari Yoshizawa

    ACS Catalysis   7 ( 6 )   3741 - 3751   2017.1

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    Recent interest in Cu-exchanged zeolite catalysts for methane hydroxylation has been broadened to small-pore Cu-zeolites such as Cu-SSZ-13 (Cu-CHA), Cu-SSZ-16 (Cu-AFX), and Cu-SSZ-39 (Cu-AEI), which were reported to produce more methanol per copper atom than the medium-pore Cu-ZSM-5 (Cu-MFI) and large-pore Cu-mordenite (Cu-MOR) zeolites do. To elucidate the nature of such fascinating catalytic activities, theoretical investigations based on density functional theory (DFT) were performed on the direct conversion of methane to methanol by [Cu2(μ-O)]2+-exchanged AEI, CHA, AFX, and MFI zeolites in periodic systems. DFT computational results show that the important activation energies for C-H bond dissociation by [Cu2(μ-O)]2+-AEI, -CHA, and -AFX zeolites are lower than those for [Cu2(μ-O)]2+-MFI zeolite. Moreover, the rate-determining methanol desorption and N2O decomposition by [2Cu]2+-AEI zeolite are also found to require low barriers, which renders [Cu2(μ-O)]2+-AEI zeolite highly active for the direct conversion of methane to methanol. Molecular orbital analyses show that AEI, CHA, AFX, and MFI zeolites exert similar confinement effects that stabilize the transition state for C-H bond cleavage. In addition, a decrease in the Cu-O-Cu angle, due to a change in the zeolite ring structure, lowers the acceptor orbital energy of [Cu2(μ-O)]2+-zeolite, which further stabilizes the transition state. We conclude that these two factors play important roles in the activation of methane.

    DOI: 10.1021/acscatal.7b00588

  • Direct Conversion of Methane to Methanol by Metal-Exchanged ZSM-5 Zeolite (Metal = Fe, Co, Ni, Cu) Reviewed International journal

    M. Haris Mahyuddin, Aleksandar Staykov, Yoshihito Shiota, Kazunari Yoshizawa

    ACS Catalysis   6 ( 12 )   8321 - 8331   2016.12

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    Metal-exchanged zeolites are known to exhibit catalytic activity in the direct conversion of methane to methanol. The influence of different metals on this reaction has been theoretically investigated by using density functional theory (DFT) calculations on a periodic system of MO+-ZSM-5 zeolite (M = Fe, Co, Ni, Cu). The results indicate a high dependence of the reaction on the metals, where the reactivity toward C-H bond dissociation is predicted to increase in the order CoO+-ZSM-5 < NiO+-ZSM-5 < FeO+-ZSM-5 < CuO+-ZSM-5 and the selectivity of methanol is predicted to increase in the order FeO+-ZSM-5 < CoO+-ZSM-5 < NiO+-ZSM-5 < CuO+-ZSM-5. The role of ZSM-5 zeolite in the catalytic activity is also investigated by comparing our calculation results with those reported for the reaction by bare MO+ species in the gas phase. We found that the nanopores of ZSM-5 zeolite exert a confinement effect which destabilizes the adsorption of methane and lowers the activation energy for the C-H bond dissociation. In addition to the conversion of methane, we investigated the direct conversion of ethane to ethanol by FeO+-ZSM-5 and found that this reaction proceeds with a lower C-H bond activation energy and a higher product selectivity in comparison to the conversion of methane to methanol by the same catalyst.

    DOI: 10.1021/acscatal.6b01721

  • A Ruthenium(III)–Oxyl Complex Bearing Strong Radical Character Reviewed International journal

    Yoshihiro Shimoyama, Tomoya Ishizuka, Hiroaki Kotani, Yoshihito Shiota, Kazunari Yoshizawa, Kaoru Mieda, Takashi Ogura, Toshihiro Okajima, Shunsuke Nozawa, Takahiko Kojima

    Chemistry - A European Journal   55 ( 45 )   14041 - 14045   2016.11

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    Proton-coupled electron-transfer oxidation of a RuII−OH2complex, having an N-heterocyclic carbene ligand, gives a RuIII−O.species, which has an electronically equivalent structure of the RuIV=O species, in an acidic aqueous solution. The RuIII−O.complex was characterized by spectroscopic methods and DFT calculations. The oxidation state of the Ru center was shown to be close to +3; the Ru−O bond showed a lower-energy Raman scattering at 732 cm−1and the Ru−O bond length was estimated to be 1.77(1) Å. The RuIII−O.complex exhibits high reactivity in substrate oxidation under catalytic conditions; particularly, benzaldehyde and the derivatives are oxidized to the corresponding benzoic acid through C−H abstraction from the formyl group by the RuIII−O.complex bearing a strong radical character as the active species.

    DOI: 10.1002/chem.201504883

  • Directional Electron Transfer in Crystals of [CrCo] Dinuclear Complexes Achieved by Chirality-Assisted Preparative Method Reviewed International journal

    Shinji Kanegawa, Yoshihito Shiota, Soonchul Kang, Kazuyuki Takahashi, Hajime Okajima, Akira Sakamoto, Tatsuya Iwata, Hideki Kandori, Kazunari Yoshizawa, Osamu Sato

    JournalJournal of the American Chemical Society   138 ( 43 )   14170 - 14173   2016.11

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    The polarization switching mechanism is used in various devices such as pyroelectric sensors and memory devices. The change in polarization mostly occurs by ion displacement. The development of materials whose polarization switches via electron transfer in order to enhance operation speed is a challenge. We devised a synthetic and crystal engineering strategy that enables the selective synthesis of a [CrCo] heterometallic dinuclear complex with a polar crystal structure, wherein polarization changes stem from intramolecular charge transfer between Co and the ligand. Polarization can be modulated both by visible-light irradiation and temperature change. The introduction of chiral ligands was paramount to the successful polarization switching in the valence tautomeric compound. Mixing Cr and Co complexes with enantiopure chiral ligands resulted in the selective formation of only pseudosymmetric [CrCo] heterometallic complexes. Furthermore, the left-handed chiral ligands preferentially interacted with their right-handed counterparts, enabling molecules to form a polar crystal structure.

    DOI: 10.1021/jacs.6b05089

  • Theoretical Study of the Catalytic Hydrogenation of Alkenes by a Disilaferracyclic Complex: Can the Fe-Si σ-Bond-Assisted Activation of H-H Bonds Allow Development of a Catalysis of Iron? Reviewed

    Tahara A, Tanaka H, Sunada Y, Shiota Y, Yoshizawa K, Nagashima H

    Journal of Organic Chemistry   81 ( 22 )   10900 - 10911   2016.11

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    Theoretical Study of the Catalytic Hydrogenation of Alkenes by a Disilaferracyclic Complex: Can the Fe-Si sigma-Bond-Assisted Activation of H-H Bonds Allow Development of a Catalysis of Iron?
    The mechanisms associated with the hydrogenation of alkenes catalyzed by the iron complex Fe(cis-CO)(2){o-(SiMe2)(2)C6H4}(2)(H)(2) (1) were investigated by DFT calculations. The complex 1 has a structure in which the iron center is bonded to four silicon atoms and two hydrides. Secondary Si center dot center dot center dot H center dot center dot center dot Si interactions were also observed. The exchange of a 1,2-bis(dimethylsilyl)benzene ligand with ethylene and hydrogen gives a disilaferracycle bearing eta(2)-(CH2 = CH2) and eta(2)-H-2 ligands. The catalytic cycle initiated from the disilaferracycle involves cleavage of a H-H linkage assisted by an Fe-Si bond to form Fe-H and n'-(H-Si) moieties (step 1), hydrogen migration from the Fe-H group to the eta(2)-(CH2 = CH2) ligand which accomplishes the insertion of ethylene into the Fe-H bond (step 2), and reaction of the resulting beta-agostic ethyl moiety with the eta(2)-(H-Si) group to form ethane on the iron atom (step 3). The octahedral geometry of 1 as well as the presence of pi-acidic CO ligands and Fe-Si sigma-bonds contributes to all of the catalytic intermediates and the transition states being in the low-spin state. Steps 1 and 3 correspond to the a-complex-assisted metathesis (sigma-CAM) mechanisms proposed by Perutz and Sabo-Etienne, suggesting that these mechanisms can assist in the design of iron-based hydrogenation catalysts operating under mild conditions.

    DOI: 10.1021/acs.joc.6b01961

  • Thermally Induced Intra-Carboxyl Proton Shuttle in a Molecular Rack-and-Pinion Cascade Achieving Macroscopic Crystal Deformation Reviewed

    You-Gui Huang, Yoshihito Shiota, Sheng-Qun Su, Shu-Qi Wu, Zi-Shuo Yao, Guo-Ling Li, Shinji Kanegawa, Soonchul Kang, Takashi Kamachi, Kazunari Yoshizawa, Katsuhiko Ariga, Osamu Sato

    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION   55 ( 47 )   14628 - 14632   2016.11

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    Proton transport via dynamic molecules is ubiquitous in chemistry and biology. However, its use as a switching mechanism for properties in functional molecular assemblies is far less common. In this study, we demonstrate how an intra-carboxyl proton shuttle can be generated in a molecular assembly akin to a rack-and-pinion cascade via a thermally induced single-crystal-to-single-crystal phase transition. In a triply interpenetrated supramolecular organic framework (SOF), a 4,4'-azopyridine (azpy) molecule connects to two biphenyl-3,3', 5,5'-tetracarboxylic acid (H4BPTC) molecules to form a functional molecular system with switchable mechanical properties. A temperature change reversibly triggers a molecular movement akin to a rack-and-pinion cascade, which mainly involves 1) an intra-carboxyl proton shuttle coupled with tilting of the azo molecules and azo pedal motion and 2) H4BPTC translation. Moreover, both the molecular motions are collective, and being propagated across the entire framework, leading to a macroscopic crystal expansion and contraction.

    DOI: 10.1002/anie.201607886

  • Mechanistic Insights into C-H Oxidations by Ruthenium(III)-Pterin Complexes: Impact of Basicity of the Pterin Ligand and Electron Acceptability of the Metal Center on the Transition States Reviewed International journal

    Hiroumi Mitome, Tomoya Ishizuka, Hiroaki Kotani, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    Journal of the American Chemical Society   138 ( 30 )   9508 - 9520   2016.8

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    A ruthenium(II) complex, [Ru(dmdmp)Cl(MeBPA)] (2) (Hdmdmp = N,N-dimethyl-6,7-dimethylpterin, MeBPA = N-methyl-N,N-bis(pyridylmethyl)amine), having a pterin derivative as a proton-accepting ligand, was synthesized and characterized. Complex 2 shows higher basicity than that of a previously reported RuII-pterin complex, [Ru(dmdmp) (TPA)]+ (1) (TPA = tris(2-pyridylmethyl)amine). On the other hand, 1e--oxidized species of 1 (1OX) exhibits higher electron-acceptability than that of 1e--oxidized 2 (2OX). Bond dissociation enthalpies (BDE) of the two RuII complexes having Hdmdmp as a ligand in proton-coupled electron transfer (PCET) to generate 1OX and 2OX were calculated to be 85 kcal mol-1 for 1OX and 78 kcal mol-1 for 2OX. The BDE values are large enough to perform H atom transfer from C-H bonds of organic molecules to the 1e--oxidized complexes through PCET. The second-order rate constants (k) of PCET oxidation reactions were determined for 1OX and 2OX. The logarithms of normalized k values were proportional to the BDE values of C-H bonds of the substrates with slopes of -0.27 for 1OX and -0.44 for 2OX. The difference between 1OX and 2OX in the slopes suggests that the transition states in PCET oxidations of substrates by the two complexes bear different polarization, as reflection of difference in the electron acceptability and basicity of 1OX and 2OX. The more basic 2OX attracts a proton from a C-H bond via a more polarized transition state than that of 1OX; on the contrary, the more electron-deficient 1OX forms less polarized transition states in PCET oxidation reactions of C-H bonds.

    DOI: 10.1021/jacs.6b03785

  • Computational Study of Cyclobutane-1,3-diylidene Dicarbenes: Ground-State Spin Multiplicity and New Strategy toward the Synthesis of Bicyclo[1.1.0]but-1(3)-enes Reviewed International journal

    Yoshiki Fujita, Manabu Abe, Yoshihito Shiota, Tatsuya Suzuki, Kazunari Yoshizawa

    Bulletin of the Chemical Society of Japan   89 ( 7 )   770 - 778   2016.7

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    Coupled-cluster calculations were performed for cyclobutane-1,3-diylidene dicarbenes 2 at the CCSD(T)//CCSD/ cc-pVDZ level of theory, in which the ground-state spin multiplicity and the structures of unique molecules were investigated in detail. The closed-shell singlet state 2(Sσπ ) with a bicyclo-[1.1.0]but-1(3)-ene (BBE) structure found to be the groundstate was much lower in energy than the corresponding singlet dicarbene structure 2(S∗∗ ), the quintet state 2(Q), and the triplet state 2(T), suggesting that the hitherto experimentally unknown BBE structure can be synthesized by the intramolecular dimerization of two carbene units. The energy gap between the BBE structures 2(Ssigma;π) and corresponding quintet states 2(Q) with electron-withdrawing substituents (X = F) at the C2 and C4 positions was found to be larger than that with electrondonating substituents (X = SiH3 ), i.e., ca. 100 kcal mol1 for2b (X = F) > ca. 85 kcal mol1 for 2a (X = H) > ca. 70 kcal mol-1 for 2c (X = SiH3 ). Two unique structures, 2(Tσ ) with a C1σC3 bond and 2(Tπ ) with a C1πC3 bond, were found to be the equilibrium structures for the triplet state of cyclobutane-1,3-diylidene dicarbenes 2.

    DOI: 10.1246/bcsj.20160051

  • Superior thermoelasticity and shape-memory nanopores in a porous supramolecular organic framework Reviewed

    You-Gui Huang, Yoshihito Shiota, Ming-Yan Wu, Sheng-Qun Su, Zi-Shuo Yao, Soonchul Kang, Shinji Kanegawa, Guo-Ling Li, Shu-Qi Wu, Takashi Kamachi, Kazunari Yoshizawa, Katsuhiko Ariga, Mao-Chun Hong, Osamu Sato

    NATURE COMMUNICATIONS   7   2016.5

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    Flexible porous materials generally switch their structures in response to guest removal or incorporation. However, the design of porous materials with empty shape-switchable pores remains a formidable challenge. Here, we demonstrate that the structural transition between an empty orthorhombic phase and an empty tetragonal phase in a flexible porous dodecatuple intercatenated supramolecular organic framework can be controlled cooperatively through guest incorporation and thermal treatment, thus inducing empty shape-memory nanopores. Moreover, the empty orthorhombic phase was observed to exhibit superior thermoelasticity, and the molecular-scale structural mobility could be transmitted to a macroscopic crystal shape change. The driving force of the shape-memory behaviour was elucidated in terms of potential energy. These two interconvertible empty phases with different pore shapes, that is, the orthorhombic phase with rectangular pores and the tetragonal phase with square pores, completely reject or weakly adsorb N-2 at 77 K, respectively.

    DOI: 10.1038/ncomms11564

  • The role of coulomb interactions for spin crossover behaviors and crystal structural transformation in novel anionic fe(III) complexes from a π-extended ono ligand Reviewed

    Murata S, Takahashi K, Sakurai T, Ohta H, Yamamoto T, Einaga Y, Shiota Y, Yoshizawa K

    Crystals   6 ( 5 )   2016.5

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    The Role of Coulomb Interactions for Spin Crossover Behaviors and Crystal Structural Transformation in Novel Anionic Fe(III) Complexes from a pi-Extended ONO Ligand
    To investigate the pi-extension effect on an unusual negative-charged spin crossover (SCO) FeIII complex with a weak N2O4 first coordination sphere, we designed and synthesized a series of anionic FeIII complexes from a pi-extended naphthalene derivative ligand. Acetonitrile-solvate tetramethylammonium (TMA) salt 1 exhibited an SCO conversion, while acetone-solvate TMA salt 2 was in a high-spin state. The crystal structural analysis for 2 revealed that two-leg ladder-like cation-anion arrays derived from pi-stacking interactions between pi-ligands of the FeIII complex anion and Coulomb interactions were found and the solvated acetone molecules were in one-dimensional channels between the cation-anion arrays. A desolvation-induced single-crystal-to-single-crystal transformation to desolvate compound 2' may be driven by Coulomb energy gain. Furthermore, the structural comparison between quasi-polymorphic compounds 1 and 2 revealed that the synergy between Coulomb and pi-stacking interactions induces a significant distortion of coordination structure of 2.

    DOI: 10.3390/cryst6050049

  • Formation and High Reactivity of the anti-Dioxo Form of High-Spin μ-Oxodioxodiiron(IV) as the Active Species That Cleaves Strong C-H Bonds Reviewed International journal

    Masahito Kodera, Shin Ishiga, Tomokazu Tsuji, Katsutoshi Sakurai, Yutaka Hitomi, Yoshihito Shiota, P. K. Sajith, Kazunari Yoshizawa, Kaoru Mieda, Takashi Ogura

    Chemistry - A European Journal   22 ( 17 )   5924 - 5936   2016.4

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    Recently, it was shown that μ-oxo-μ-peroxodiiron(III) is converted to high-spin μ-oxodioxodiiron(IV) through O-O bond scission. Herein, the formation and high reactivity of the anti-dioxo form of high-spin μ-oxodioxodiiron(IV) as the active oxidant are demonstrated on the basis of resonance Raman and electronic-absorption spectral changes, detailed kinetic studies, DFT calculations, activation parameters, kinetic isotope effects (KIE), and catalytic oxidation of alkanes. Decay of μ-oxodioxodiiron(IV) was greatly accelerated on addition of substrate. The reactivity order of substrates is toluene<ethylbenzene≈cumene<trans-β-methylstyrene. The rate constants increased proportionally to the substrate concentration at low substrate concentration. At high substrate concentration, however, the rate constants converge to the same value regardless of the kind of substrate. This is explained by a two-step mechanism in which anti-μ-oxodioxodiiron(IV) is formed by syn-to-anti transformation of the syn-dioxo form and reacts with substrates as the oxidant. The anti-dioxo form is 620 times more reactive in the C-H bond cleavage of ethylbenzene than the most reactive diiron system reported so far. The KIE for the reaction with toluene/[D8]toluene is 95 at -30 °C, which the largest in diiron systems reported so far. The present diiron complex efficiently catalyzes the oxidation of various alkanes with H2O2. Strong anti oxidant: A high-spin μ-oxodioxodiiron(IV) species undergoes transformation from the syn-dioxo to the anti-dioxo form, which cleaves strong C-H bonds of alkanes. The high-spin anti-dioxodiiron(IV) species with a sterically less hindered structure (see figure) is a highly reactive and selective oxidant. These results provide insight into the high reactivity of the active species Q of soluble methane monooxygenases and the development of efficient alkane oxidation catalysts.

    DOI: 10.1002/chem.201600048

  • Push–pull fluorenones and benzazulenequinones: regioselective [4+2] and [2+2] cycloadditions of benzopentalenequinone derivative and alkynes bearing an aniline moiety Reviewed International journal

    Shin ichiro Kato, Tomokazu Kijima, Yoshihito Shiota, Toshitada Yoshihara, Seiji Tobita, Kazunari Yoshizawa, Yosuke Nakamura

    Tetrahedron Letters   4 ( 57 )   4604 - 4607   2016.4

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    The reaction of benzopentalenequinone with alkynes bearing an aniline moiety provides access to two classes of push–pull chromophores with interesting optoelectronic properties. The regioselective [4+2] cycloaddition/[4+1] retrocycloaddition sequence gives fluorenone derivatives, and the formal regioselective [2+2] cycloaddition/ring-opening reaction in polar solvents generates hitherto unknown benzazulenequinone derivatives.

    DOI: 10.1016/j.tetlet.2016.09.002

  • Possible Peroxo State of the Dicopper Site of Particulate Methane Monooxygenase from Combined Quantum Mechanics and Molecular Mechanics Calculations Reviewed

    Shuhei Itoyama, Kazuki Doitomi, Takashi Kamachi, Yoshihito Shiota, Kazunari Yoshizawa

    INORGANIC CHEMISTRY   55 ( 6 )   2771 - 2775   2016.3

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    Enzymatic methane hydroxylation is proposed to efficiently occur at the dinuclear copper site of particulate methane monooxygenase (pMMO), which is an integral membrane metalloenzyme in methanotrophic bacteria. The resting state and a possible peroxo state of the dicopper active site of pMMO are discussed by using combined quantum mechanics and molecular mechanics calculations on the basis of reported X-ray crystal structures of the resting state of pMMO by Rosenzweig and co-workers. The dicopper site has a unique structure, in which one copper is coordinated by two histidine imidazoles and another is chelated by a histidine imidazole and primary amine of an N-terminal histidine. The resting state of the dicopper site is assignable to the mixed-valent (CuCuII)-Cu-I state from a computed Cu-Cu distance of 2.62 angstrom from calculations at the B3LYP-D/TZVP level of theory. A mu-eta(2):eta(2)-peroxo-Cu-2(II) structure similar to those of hemocyanin and tyrosinase is reasonably obtained by using the resting state structure and dioxygen. Computed Cu-Cu and O-O distances are 3.63 and 1.46 angstrom, respectively, in the open-shell singlet state. Structural features of the dicopper peroxo species of pMMO are compared with those of hemocyanin and tyrosinase and synthetic dicopper model compounds. Optical features of the mu-eta(2):eta(2)-peroxo-Cu-2(II) state are calculated and analyzed with TD-DFT calculations.

    DOI: 10.1021/acs.inorgchem.5b02603

  • Homogeneous Photocatalytic Water Oxidation with a Dinuclear CoIII-Pyridylmethylamine Complex Reviewed International journal

    Tomoya Ishizuka, Atsuko Watanabe, Hiroaki Kotani, Dachao Hong, Kenta Satonaka, Tohru Wada, Yoshihito Shiota, Kazunari Yoshizawa, Kazuaki Ohara, Kentaro Yamaguchi, Satoshi Kato, Shunichi Fukuzumi, Takahiko Kojima

    Inorganic chemistry   55 ( 3 )   1154 - 1164   2016.2

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    A bis-hydroxo-bridged dinuclear CoIII-pyridylmethylamine complex (1) was synthesized and the crystal structure was determined by X-ray crystallography. Complex 1 acts as a homogeneous catalyst for visible-light-driven water oxidation by persulfate (S2O82-) as an oxidant with [RuII(bpy)3]2+ (bpy = 2,2′-bipyridine) as a photosensitizer affording a high quantum yield (44%) with a large turnover number (TON = 742) for O2 formation without forming catalytically active Co-oxide (CoOx) nanoparticles. In the water-oxidation process, complex 1 undergoes proton-coupled electron-transfer (PCET) oxidation as a rate-determining step to form a putative dinuclear bis-μ-oxyl CoIII complex (2), which has been suggested by DFT calculations. Catalytic water oxidation by 1 using [RuIII(bpy)3]3+ as an oxidant in a H216O and H218O mixture was examined to reveal an intramolecular O-O bond formation in the two-electron-oxidized bis-μ-oxyl intermediate, prior to the O2 evolution.

    DOI: 10.1021/acs.inorgchem.5b02336

  • Synthesis and structure of a water-soluble μ-η11-N<inf>2</inf> dinuclear RuII complex with a polyamine ligand Reviewed

    Yoshimoto K, Yatabe T, Matsumoto T, Robertson A, Nakai H, Tanaka H, Kamachi T, Shiota Y, Yoshizawa K, Asazawa K, Tanaka H, Ogo S

    Chemistry Letters   45 ( 2 )   149 - 151   2016.2

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    Synthesis and Structure of a Water-soluble mu-eta(1):eta(1)-N-2 Dinuclear Ru-II Complex with a Polyamine Ligand
    We report the first example of a mu-eta(1):eta(1)-N-2 dinuclear Run complex with a polyamine ligand and elucidate the structure by means of X-ray analysis. The N N stretching vibration has been observed at 1994 cm(-1) by Raman spectroscopy, which is the lowest value of all the known N-2-coordinated Run complexes. This low value strongly suggests the N N. bond is primed for activation.

    DOI: 10.1246/cl.151004

  • Persistent four-coordinate iron-centered radical stabilized by π-donation Reviewed International journal

    Yusuke Sunada, Shintaro Ishida, Fumiya Hirakawa, Yoshihito Shiota, Kazunari Yoshizawa, Shinji Kanegawa, Osamu Sato, Hideo Nagashima, Takeaki Iwamoto

    Chemical Science   7 ( 1 )   191 - 198   2016.1

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    Dinuclear iron carbonyl complex 2, which contains an elongated unsupported Fe-Fe bond, was synthesized by the reaction between Fe 2 (CO) 9 and phosphinyl radical 1. Thermal Fe-Fe bond homolysis led to the generation of a four-coordinate carbonyl-based iron-centered radical, 3, which is stabilized by π-donation. Complex 3 exhibited high reactivity toward organic radicals to form diamagnetic five-coordinate Fe(ii) complexes.

    DOI: 10.1039/c5sc02601f

  • Heterometallic FeIII/K Coordination Polymer with a Wide Thermal Hysteretic Spin Transition at Room Temperature Reviewed International journal

    Soonchul Kang, Yoshihito Shiota, Akira Kariyazaki, Shinji Kanegawa, Kazunari Yoshizawa, Osamu Sato

    Chemistry - A European Journal   22 ( 2 )   532 - 538   2016.1

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    The anionic FeIII complex exhibiting cooperative spin transition with a wide thermal hysteresis near room temperature, K[Fe(5-Brthsa)2] (5-Brthsa-H2=5-bromosalicylaldehyde thiosemicarbazone), is reported. The hysteresis (Δ=69 K in the first cycle) shows a one-step transition in heating mode and a two-step transition in cooling mode. X-ray structure analysis showed that the coexistence of hydrogen bond and cation-π interactions, as well as alkali metal coordination bonds, to give 2D coordination polymer structure. This result is contrary to previous reports of broad thermal hysteresis induced by coordination bonds of FeII spin crossover coordination polymers (with 1D/3D structures), and by strong intermolecular interactions in the molecular packing through π-π stacking or hydrogen-bond networks. As a consequence, the importance, or the very good suitability of alkali metal-based coordination bonds and cation-π interactions for communicating cooperative interactions in spin-crossover (SCO) compounds must be reconsidered.

    DOI: 10.1002/chem.201503392

  • A New Family of Anionic FeIII Spin Crossover Complexes Featuring a Weak-Field N2O4 Coordination Octahedron Reviewed International journal

    Kazuyuki Takahashi, Kiko Kawamukai, Mitsunobu Okai, Tomoyuki Mochida, Takahiro Sakurai, Hitoshi Ohta, Takashi Yamamoto, Yasuaki Einaga, Yoshihito Shiota, Kazunari Yoshizawa

    JournalChemistry - A European Journal   22 ( 4 )   1253 - 1257   2016.1

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    Unprecedented anionic FeIII spin crossover (SCO) complexes involving a weak-field O,N,O-tridentate ligand were discovered. The SCO transition was evidenced by the temperature variations in magnetic susceptibility, Mössbauer spectrum, and coordination structure. The DFT calculations suggested that larger coefficients on the azo group in the HOMO-1 of a ligand might contribute to the enhancement of a ligand-field splitting energy. The present anionic SCO complex also exhibited the light- induced excited-spin-state trapping effect. Photoinduced spin transition: Unprecedented anionic spin crossover (SCO) complexes involving a weak-field FeIIIN2O4 coordination sphere were discovered. The tetramethylammonium salt of the depicted SCO anion exhibited the light-induced excited-spin-state trapping effect, which is quite rare in FeIII SCO complexes (see scheme).

    DOI: 10.1002/chem.201504883

  • Assembling an alkyl rotor to access abrupt and reversible crystalline deformation of a cobalt(II) complex Reviewed

    Sheng-Qun Su, Takashi Kamachi, Zi-Shuo Yao, You-Gui Huang, Yoshihito Shiota, Kazunari Yoshizawa, Nobuaki Azuma, Yuji Miyazaki, Motohiro Nakano, Goro Maruta, Sadamu Takeda, Soonchul Kang, Shinji Kanegawa, Osamu Sato

    NATURE COMMUNICATIONS   6   2015.11

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    Harnessing molecular motion to reversibly control macroscopic properties, such as shape and size, is a fascinating and challenging subject in materials science. Here we design a crystalline cobalt(II) complex with an n-butyl group on its ligands, which exhibits a reversible crystal deformation at a structural phase transition temperature. In the low-temperature phase, the molecular motion of the n-butyl group freezes. On heating, the n-butyl group rotates ca. 100 degrees around the C-C bond resulting in 6-7% expansion of the crystal size along the molecular packing direction. Importantly, crystal deformation is repeatedly observed without breaking the single-crystal state even though the shape change is considerable. Detailed structural analysis allows us to elucidate the underlying mechanism of this deformation. This work may mark a step towards converting the alkyl rotation to the macroscopic deformation in crystalline solids.

    DOI: 10.1038/ncomms9810

  • Redox-Noninnocent Behavior of Tris(2-pyridylmethyl)amine Bound to a Lewis Acidic Rh(III) Ion Induced by C-H Deprotonation Reviewed

    Hiroaki Kotani, Takumi Sugiyama, Tomoya Ishizuka, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   137 ( 35 )   11222 - 11225   2015.9

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    Rh(III) complexes having tris(2-pyridylmethyl)amine (TPA) and its derivative as tetradentate ligands showed reversible deprotonation at a methylene moiety of the TPA ligands upon addition of a strong base as confirmed by spectroscopic measurements and X-ray crystallography. Deprotonation selectively occurred at the axial methylene moiety rather than equatorial counterparts because of the thermodynamic stability of corresponding deprotonated complexes. One-electron oxidation of the deprotonated Rh(III) TPA complex afforded a unique TPA radical bound to the Rh(III) center by a ligand-centered oxidation. This is the first example to demonstrate emergence of the redox-noninnocent character of the TPA ligand.

    DOI: 10.1021/jacs.5b06237

  • Proton-Assisted Mechanism of NO Reduction on a Dinuclear Ruthenium Complex Reviewed

    Tatsuya Suzuki, Hiromasa Tanaka, Yoshihito Shiota, P. K. Sajith, Yasuhiro Arikawa, Kazunari Yoshizawa

    INORGANIC CHEMISTRY   54 ( 15 )   7181 - 7191   2015.8

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    Density-functional-theory (DFT) calculations are performed for the proposal of a plausible mechanism on the reduction of NO to N2O by a dinuclear ruthenium complex, reported by Arikawa and co-workers [J. Am. Chem. Soc. 2007, 129, 14160]. On the basis of the experimental fact that the reduction proceeds under strongly acidic conditions, the role of protons in the mechanistic pathways is investigated with model complexes, where one or two NO ligands are protonated. The reaction mechanism of the NO reduction is partitioned into three steps: reorientation of N2O2 (cis-NO dimer), O-N bond cleavage, and N2O elimination. A key finding is that the protonation of the NO ligand(s) significantly reduces the activation barrier in the rate-determining reorientation step. The activation energy of 43.1 kcal/mol calculated for the proton-free model is reduced to 30.2 and 17.6 kcal/mol for the mono- and diprotonated models, respectively. The protonation induces the electron transfer from the Ru(II)Ru(II) core to the O=N-N=O moiety to give a Ru(III)Ru(III) core and a hyponitrite (O-N=N-O)(2-) species. The formation of the hyponitrite species provides an alternative pathway for the N2O2 reorientation, resulting in the lower activation energies in the presence of proton(s). The protonation also has a marginal effect on the O-N bond cleavage and the N2O elimination steps. Our calculations reveal a remarkable role of protons in the NO reduction via N2O formation and provide new insights into the mechanism of NO reduction catalyzed by metalloenzymes such as nitric oxide reductase (NOR) that contains a diiron active site.

    DOI: 10.1021/acs.inorgchem.5b00394

  • cis-1,2-Aminohydroxylation of Alkenes Involving a Catalytic Cycle of Osmium(III) and Osmium(V) Centers: Os-V(O)(NHTs) Active Oxidant with a Macrocyclic Tetradentate Ligand Reviewed

    Hideki Sugimoto, Akine Mikami, Kenichiro Kai, P. K. Sajith, Yoshihito Shiota, Kazunari Yoshizawa, Kaori Asano, Takeyuki Suzuki, Shinobu Itoh

    INORGANIC CHEMISTRY   54 ( 14 )   7073 - 7082   2015.7

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    Catalytic activity of [Os-III(OH)(H2O)(L-N4Me2)](PF6)(2) (1: L-N4Me2 = N,N'-dimethyl-2,11-diaza-[3,3](2,6)pyridinophane) in 1,2-cis-aminohydroxylation of alkenes with sodium N-chloro-4-methylbenzenesulfonamide (chloramine-T) is explored. Simple alkenes as well as those containing several types of substituents are converted to the corresponding 1,2-aminoalcohols in modest to high yields. The aminoalcohol products have exclusively cis conformation with respect to the introduced -OH and -NHTs groups. The spectroscopic measurements including cold mass spectroscopic study of the reaction product of complex 1 and chloromine-T as well as density functional theory (DFT) calculations indicate that an oxido-aminato-osmium(V) species [Os-V(O)(NHTs)(L-N4Me2)](PF6)(2) (2) is an active oxidant for the aminohydroxylation. The DFT calculations further indicate that the reaction involves a [3 + 2] cycloaddition between 2 and alkene, and the regioselectivity in the aminohydroxylation of unsymmetrical alkenes is determined by the orientation that bears less steric hindrance from the tosylamino group, which leads to the energetically more preferred product isomer.

    DOI: 10.1021/acs.inorgchem.5601083

  • Gas-phase acidity of 1,1-bis(trifluoromethanesulfonyl)propane derivatives and related compounds: experimental and theoretical studies Reviewed

    Min Zhang, Takaaki Sonoda, Yoshihito Shiota, Masaaki Mishima, Hikaru Yanai, Masaya Fujita, Takeo Taguchi

    JOURNAL OF PHYSICAL ORGANIC CHEMISTRY   28 ( 3 )   181 - 186   2015.3

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    The gas-phase acidity (GA) of a series of 1,1-bis(trifluoromethanesulfonyl)propane derivatives, Tf2CHCH2CH(R-1)R-2, and Tf2CHCH2Ar (Ar=phenol derivatives) was determined by measuring proton-transfer equilibria using a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer and by computing the free energy of the deprotonated carbanions and the corresponding neutrals. The effects of R-1 and R-2 or Ar groups on the acidity were examined. In Tf2CHCH2CH(R-1)R-2, the GA values calculated using the conformers of neutral molecules that are free from the intramolecular hydrogen-bonding interaction between the acidic hydrogen atom of the Tf2CH moiety and R-1 or R-2 group and between the hydrogen atom of the (CHRR2)-R-1 moiety and the SO2CF3 group were correlated in terms of an equation, GA=-17.0 sigma sigma(I)+3.4 sigma sigma+299.5. On the basis of this correlation, it was elucidated that the intramolecular hydrogen bonding or dipole-dipole interaction in the neutral molecule weakens significantly the acidity. In Tf2CHCH2Ar (5, 6 and 7), the GA was strengthened by the strong hydrogen-bonding interaction between the phenolic hydrogen in the aromatic moiety and the SO2CF3 group in the conjugate anion compared with that in the neutral molecule. Copyright (c) 2014 John Wiley & Sons, Ltd.

    DOI: 10.1002/poc.3304

  • Controlling the redox properties of a pyrroloquinolinequinone (PQQ) derivative in a ruthenium(ii) coordination sphere Reviewed International journal

    Hiroumi Mitome, Tomoya Ishizuka, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    Dalton Transactions   44 ( 7 )   3151 - 3158   2015.2

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    Ruthenium(ii) complexes of PQQTME, a trimethyl ester derivative of redox-active PQQ (pyrroloquinolinequinone), were prepared using a tridentate ligand, 2,2′:6′,2′′-terpyridine (terpy) as an auxiliary ligand. The characterization of the complexes was performed by spectroscopic methods, X-ray crystallography, and electrochemical measurements. In one complex, the pyridine site of PQQTME binds to the [RuII(terpy)] unit as a tridentate ligand, and a silver(i) ion is coordinated by the quinone moiety in a bidentate fashion. In contrast, another complex includes the [RuII(terpy)] unit at the bidentate quinone moiety of the PQQTME ligand. The difference in the coordination modes of the complexes exhibits a characteristic difference in the stability of metal coordination and also in the reversibility of the reduction processes of the PQQTME ligand. It should be noted that an additional metal-ion-binding to the PQQTME ligand largely raises the 1e--reduction potential of the ligand. In addition, we succeeded in the characterization of the 1e--reduced species of the complexes, where the unpaired electron was delocalized in the π-conjugated system of the PQQTME- ligand, using UV-Vis absorption and ESR spectroscopies.

  • Formation and characterization of a reactive chromium(V)-oxo complex: Mechanistic insight into hydrogen-atom transfer reactions Reviewed International journal

    Hiroaki Kotani, Suzue Kaida, Tomoya Ishizuka, Miyuki Sakaguchi, Takashi Ogura, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    Chemical Science   6 ( 2 )   945 - 955   2015.2

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    A mononuclear Cr(V)-oxo complex, [CrV(O)(6-COO--tpa)](BF4)2 (1; 6-COO--tpa = N,N-bis(2-pyridylmethyl)-N-(6-carboxylato-2-pyridylmethyl)amine) was prepared through the reaction of a Cr(III) precursor complex with iodosylbenzene as an oxidant. Characterization of 1 was achieved using ESI-MS spectrometry, electron paramagnetic resonance, UV-vis, and resonance Raman spectroscopies. The reduction potential (Ered) of 1 was determined to be 1.23 V vs. SCE in acetonitrile based on analysis of the electron-transfer (ET) equilibrium between 1 and a one-electron donor, [RuII(bpy)3]2+ (bpy = 2,2′-bipyridine). The reorganization energy (λ) of 1 was also determined to be 1.03 eV in ET reactions from phenol derivatives to 1 on the basis of the Marcus theory of ET. The smaller λ value in comparison with that of an Fe(IV)-oxo complex (2.37 eV) is caused by the small structural change during ET due to the dπ character of the electron-accepting LUMO of 1. When benzyl alcohol derivatives (R-BA) with different oxidation potentials were employed as substrates, corresponding aldehydes were obtained as the 2e--oxidized products in moderate yields as determined from 1H NMR and GC-MS measurements. One-step UV-vis spectral changes were observed in the course of the oxidation reactions of BA derivatives by 1 and a kinetic isotope effect (KIE) was observed in the oxidation reactions for deuterated BA derivatives at the benzylic position as substrates. These results indicate that the rate-limiting step is a concerted proton-coupled electron transfer (PCET) from substrate to 1. In sharp contrast, in the oxidation of trimethoxy-BA (Eox = 1.22 V) by 1, trimethoxy-BA radical cation was observed by UV-vis spectroscopy. Thus, it was revealed that the mechanism of the oxidation reaction changed from one-step PCET to stepwise ET-proton transfer (ET/PT), depending on the redox potentials of R-BA.

    DOI: 10.1039/c4sc02285h

  • A ferromagnetically coupled Fe-42 cyanide-bridged nanocage Reviewed

    Soonchul Kang, Hui Zheng, Tao Liu, Kohei Hamachi, Shinji Kanegawa, Kunihisa Sugimoto, Yoshihito Shiota, Shinya Hayami, Masaki Mito, Tetsuya Nakamura, Motohiro Nakano, Michael L. Baker, Hiroyuki Nojiri, Kazunari Yoshizawa, Chunying Duan, Osamu Sato

    Nature Communications   6   2015.1

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    Self-assembly of artificial nanoscale units into superstructures is a prevalent topic in science. In biomimicry, scientists attempt to develop artificial self-assembled nanoarchitectures. However, despite extensive efforts, the preparation of nanoarchitectures with superior physical properties remains a challenge. For example, one of the major topics in the field of molecular magnetism is the development of high-spin (HS) molecules. Here, we report a cyanide-bridged magnetic nanocage composed of 18 HS iron(III) ions and 24 low-spin iron(II) ions. The magnetic iron(III) centres are ferromagnetically coupled, yielding the highest ground-state spin number (S = 45) of any molecule reported to date.

    DOI: 10.1038/ncomms6955

  • Mechanistic study of methanol oxidation by Ru-IV-oxo complexes Reviewed

    Yoshihito Shiota, Shoya Takahashi, Shingo Ohzu, Tomoya Ishizuka, Takahiko Kojima, Kazunari Yoshizawa

    JOURNAL OF PORPHYRINS AND PHTHALOCYANINES   19 ( 1-3 )   417 - 426   2015.1

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    The catalytic conversion of methanol to formaldehyde by three kinds of non-porphyrin Ru complexes, (RuO)-O-IV(TPA) (TPA = tris(2-pyridylmethyl) amine) (1a), (RuO)-O-IV(6-COO-TPA) (6-COO-TPA = 2-(6-carboxyl-pyridyl)methyl-bis(2-pyridylmethyl)amine) (1b), and (RuO)-O-IV(N4Py) (N4Py = N, N-bis(2-pyridyl-methyl)-N-bis(2-pyridyl)methylamine) (1c), is discussed by using density functional theory (DFT) calculations. There are two possible reaction pathways for the oxidation of methanol to formaldehyde with respect to the first hydrogen abstraction from the methyl group (path 1) and the hydroxyl group (path 2). Path 1 and path 2 involve the hydroxymethyl radical (center dot CH2OH) and the methoxyl radical (CH3O center dot), respectively, as an intermediate. DFT calculations demonstrate that the two pathways are energetically comparable in the reactions by the three Ru-IV-oxo complexes. The reactions with 1a and 1c are initiated by the C-H bond dissociation with activation barriers of 22.2 and 21.4 kcal/mol, respectively, while the reaction with 1b is initiated by the O-H bond dissociation with an activation barrier of 18.1 kcal/mol. However, the calculations showed that the rate-determining step is the H-atom abstraction from the CH3 group of methanol in all the pathways. These results are in good agreement with kinetic analysis of the reactions by the Ru-IV-oxo complexes, being useful for considering the mechanism of methanol oxidation.

    DOI: 10.1142/S1088424615500285

  • Molecular motor-driven abrupt anisotropic shape change in a single crystal of a Ni complex Reviewed

    Zi-Shuo Yao, Masaki Mito, Takashi Kamachi, Yoshihito Shiota, Kazunari Yoshizawa, Nobuaki Azuma, Yuji Miyazaki, Kazuyuki Takahashi, Kuirun Zhang, Takumi Nakanishi, Soonchul Kang, Shinji Kanegawa, Osamu Sato

    NATURE CHEMISTRY   6 ( 12 )   1079 - 1083   2014.12

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    Many molecular machines with controllable molecular-scale motors have been developed. However, transmitting molecular movement to the macroscopic scale remains a formidable challenge. Here we report a single crystal of a Ni complex whose shape changes abruptly and reversibly in response to thermal changes at around room temperature. Variable-temperature single-crystal X-ray diffraction studies show that the crystalline shape change is induced by an unusual 90 degrees rotation of uniaxially aligned oxalate molecules. The oxalate dianions behave as molecular-scale rotors, with their movement propagated through the entire crystalline material via intermolecular hydrogen bonding. Consequently, the subnanometrescale changes in the oxalate molecules are instantly amplified to a micrometre-scale contraction or expansion of the crystal, accompanied by a thermal hysteresis loop. The shape change in the crystal was clearly detected under an optical microscope. The large directional deformation and prompt response suggest a role for this material in microscale or nanoscale thermal actuators.

    DOI: 10.1038/NCHEM.2092

  • Tetranuclear Ruthenium(II) Complex with a Dinucleating Ligand Forming Multi-Mixed-Valence States Reviewed

    Shingo Ohzu, Tomoya Ishizuka, Hiroaki Kotani, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    INORGANIC CHEMISTRY   53 ( 24 )   12677 - 12679   2014.12

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    A square-shaped tetranuclear ruthenium(II) complex, [(Ru4Cl5)-Cl-II(bpmpm)(2)](3+) [1; bpmpm = 4,6-bis[[N,N-bis(2'-pyridylmethyl)amino]methyl]pyrimidine], exhibited four reversible and stepwise one-electron-oxidation processes: chemical oxidation of 1 formed three different mixed-valence states, in one of which the charge is partially delocalized on the two Ru centers, to be evidenced by observation of an intervalence charge-transfer absorption band, categorized into the RobinDay class II.

    DOI: 10.1021/ic502422u

  • Molecular motor-driven abrupt anisotropic shape change in a single crystal of a Ni complex Reviewed

    Zi-Shuo Yao, Masaki Mito, Takashi Kamachi, Yoshihito Shiota, Kazunari Yoshizawa, Nobuaki Azuma, Yuji Miyazaki, Kazuyuki Takahashi, Kuirun Zhang, Takumi Nakanishi, Soonchul Kang, Shinji Kanegawa, Osamu Sato

    NATURE CHEMISTRY   6 ( 12 )   1079 - 1083   2014.12

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    Many molecular machines with controllable molecular-scale motors have been developed. However, transmitting molecular movement to the macroscopic scale remains a formidable challenge. Here we report a single crystal of a Ni complex whose shape changes abruptly and reversibly in response to thermal changes at around room temperature. Variable-temperature single-crystal X-ray diffraction studies show that the crystalline shape change is induced by an unusual 90 degrees rotation of uniaxially aligned oxalate molecules. The oxalate dianions behave as molecular-scale rotors, with their movement propagated through the entire crystalline material via intermolecular hydrogen bonding. Consequently, the subnanometrescale changes in the oxalate molecules are instantly amplified to a micrometre-scale contraction or expansion of the crystal, accompanied by a thermal hysteresis loop. The shape change in the crystal was clearly detected under an optical microscope. The large directional deformation and prompt response suggest a role for this material in microscale or nanoscale thermal actuators.

    DOI: 10.1038/NCHEM.2092

  • Binding of Scandium Ions to Metalloporphyrin-Flavin Complexes for Long-Lived Charge Separation Reviewed

    Takahiko Kojima, Ryosuke Kobayashi, Tomoya Ishizuka, Shinya Yamakawa, Hiroaki Kotani, Tatsuaki Nakanishi, Kei Ohkubo, Yoshihito Shiota, Kazunari Yoshizawa, Shunichi Fukuzumi

    CHEMISTRY-A EUROPEAN JOURNAL   20 ( 47 )   15518 - 15532   2014.11

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    A porphyrin-flavin-linked dyad and its zinc and palladium complexes (MPor-Fl:2-M, M = 2H, Zn, and Pd) were newly synthesized and the X-ray crystal structure of 2-Pd was determined. The photodynamics of 2-M were examined by femto-and nanosecond laser flash photolysis measurements. Photoinduced electron transfer (ET) in 2-H-2 occurred from the singlet excited state of the porphyrin moiety (H(2)Por) to the flavin (Fl) moiety to produce the singlet charge-separated (CS) state (1)(H(2)Por(center dot+)-Fl(center dot-)), which decayed through back ET (BET) to form (3)[H(2)Por]*-Fl with rate constants of 1.2-10(10) and 1.2-10(9) s(-1), respectively. Similarly, photoinduced ET in 2-Pd afforded the singlet CS state, which decayed through BET to form (3)[PdPor]*-Fl with rate constants of 2.1-10(11) and 6.0-10(10) s(-1), respectively. The rate constant of photoinduced ET and BET of 2-M were related to the ET and BET driving forces by using the Marcus theory of ET. One and two Sc3+ ions bind to the flavin moiety to form the Fl-Sc3+ and Fl-(Sc3+)(2) complexes with binding constants of K-1 = 2.2-10(5)m(-1) and K-2 = 1.8-10(3)m(-1), respectively. Other metal ions, such as Y3+, Zn2+, and Mg2+, form only 1:1 complexes with flavin. In contrast to 2-M and the 1:1 complexes with metal ions, which afforded the short-lived singlet CS state, photoinduced ET in 2-Pd center dot center dot center dot Sc3+ complexes afforded the triplet CS state (3[PdPorC(center dot+)-Fl center dot--(Sc3+)(2)]), which exhibited a remarkably long lifetime of tau = 110 ms (k(BET) = 9.1 s(-1)).

    DOI: 10.1002/chem.201403960

  • Role of Acidic Proton in the Decomposition of NO over Dimeric Cu(I) Active Sites in Cu-ZSM-5 Catalyst: A QM/MM Study Reviewed

    P. K. Sajith, Yoshihito Shiota, Kazunari Yoshizawa

    ACS CATALYSIS   4 ( 6 )   2075 - 2085   2014.6

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    The influence of protons on the mechanism of the direct decomposition of NO over adjacent dimeric Cu(I) active sites in zeolite is theoretically investigated by using ONIOM (QM/MM) calculations with two dicopper model systems IT and 2T, where the Cu(I) atoms are separated by one and two SiO4 tetrahedra, respectively. The reaction proceeds through the formation of N2O as a reaction intermediate and further its decomposition into oxygen and nitrogen. The present study shows that the presence of proton plays an important role in the production of N2O from two NO molecules. In the proton-free mechanism, this process requires a large activation barrier of 56.3 and 55.3 kcal/mol on IT and 2T, respectively, while the inclusion of protons reduces it to 31.4 and 17.3 kcal/mol. The significant decrease in the activation barrier is due to the strengthening of the N-N bond of the formed NO dimer upon protonation, which facilitates the formation of N2O. On the other hand, the presence of protons disfavors the decomposition of N2O and needs an activation barrier of 6-9 kcal/mol higher than that of the corresponding reaction in the absence of protons. The stable intermediate Cu-OH+-Cu formed in the proton-assisted mechanism is responsible for the larger activation energy for N2O decomposition. The proton-assisted NO decomposition mechanism is in agreement with the experimental observation that the decomposition of N2O as well as O-2 desorption are the governing reaction steps in the decomposition of NO. The present study explains the role of the Cu-O-Cu species in the NO decomposition reaction. The results disclosed herein will also pave a way to understanding the mechanism of the reductive N-N coupling of NO molecules catalyzed by metalloenzymes and transition-metal catalysts.

    DOI: 10.1021/cs500223z

  • Hydrogen atom abstraction reactions independent of C-H bond dissociation energies of organic substrates in water: Significance of oxidant-substrate adduct formation Reviewed International journal

    Tomoya Ishizuka, Shingo Ohzu, Hiroaki Kotani, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    Chemical Science   5 ( 4 )   1429 - 1436   2014.4

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    Detailed kinetic studies on the oxidation reactions of organic substrates such as methanol with RuIVO complexes as oxidants, formed electrochemically in water, have been conducted to elucidate the reaction mechanism. The rate constants of the oxidation reactions exhibited saturation behaviours relative to the substrate concentration, regardless of the oxidants and the substrates employed. This indicates the existence of a pre-equilibrium process based on the adduct formation between the RuIVO oxidant and the substrate. Herein, we have experimentally confirmed that the driving force of the adduct formation is the hydrogen bonding between the oxidants and alcohols even in water. In addition, we have investigated the kinetic isotope effects (KIE) on the oxidation reaction using methanol and its deuterated derivatives and as a result observed moderate KIE values for the C-H bond of methanol. We have also revealed the independency of the reaction rates from the bond dissociation enthalpies of the C-H bonds of the substrates. This independency is probably derived from the tightly condensed transition state, whose energy level is strongly controlled by the activation entropy but less sensitive to the activation enthalpy.

    DOI: 10.1039/c3sc53002g

  • Role of tyrosine residue in methane activation by pMMO Reviewed

    K. Yoshizawa, Y. Shiota, G. Juhasz

    JOURNAL OF BIOLOGICAL INORGANIC CHEMISTRY   19   S216 - S216   2014.3

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  • Roles of carboxylate donors in O-O bond scission of peroxodi-iron(iii) to high-spin oxodi-iron(iv) with a new carboxylate-containing dinucleating ligand Reviewed International journal

    Masahito Kodera, Tomokazu Tsuji, Tomohiro Yasunaga, Yuka Kawahara, Tomoya Hirano, Yutaka Hitomi, Takashi Nomura, Takashi Ogura, Yoshio Kobayashi, P. K. Sajith, Yoshihito Shiota, Kazunari Yoshizawa

    Chemical Science   5 ( 6 )   2282 - 2292   2014.1

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    Dioxygen activation proceeds via O-O bond scission of peroxodi-iron(iii) to high-spin oxodi-iron(iv) in soluble methane mono-oxygenase (sMMO). Recently, we have shown that reversible O-O bond scission of peroxodi-iron(iii) to high-spin oxodi-iron(iv) is attained with a bis-tpa type dinucleating ligand, 6-hpa. In this study, a new carboxylate-containing dinucleating ligand, 1,2-bis[2-(N-2-pyridylmethyl-N-glycinylmethyl)-6-pyridyl]ethane (H 2BPG2E) and its μ-oxodiaquadi-iron(iii) complexes [Fe2(μ-O)(H2O)2(BPG2E)]X 2 [X = ClO4 (2a) or OTf (2b)] were synthesized to mimic a common carboxylate-rich coordination environment in O2-activating non-heme di-iron enzymes including sMMO. The crystal structures of 2a and 2b revealed that BPG2E prefers a syn-diaqua binding mode. 2b catalyzed the epoxidation of alkenes with H2O2. A new purple species was formed upon reaction of 2b with H2O2, and characterized by the elemental analysis and spectral and kinetic studies. These clearly showed that the purple species was a μ-oxo-μ-peroxodi-iron(iii), and converted to high-spin μ-oxodioxodi-iron(iv) via rate-determining reversible O-O bond scission. In comparison of BPG2E with 6-hpa, it is shown that the carboxylate donor stabilizes the Fe-O-O-Fe structure of the peroxo complex due to the structural effect to retard O-O bond scission. This may shed light on the roles of carboxylate donors in the dioxygen activation of non-heme di-iron enzymes.

    DOI: 10.1039/c3sc51541a

  • A light-induced spin crossover actuated single-chain magnet Reviewed

    Tao Liu, Hui Zheng, Soonchul Kang, Yoshihito Shiota, Shinya Hayami, Masaki Mito, Osamu Sato, Kazunari Yoshizawa, Shinji Kanegawa, Chunying Duan

    NATURE COMMUNICATIONS   4   2013.11

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    Both spin-crossover complexes and molecular nanomagnets display bistable magnetic states, potentially behaving as elementary binary units for information storage. It is a challenge to introduce spin-crossover units into molecular nanomagnets to switch the bistable state of the nanomagnets through external stimuli-tuned spin crossover. Here we report an iron(II) spin-crossover unit and paramagnetic iron(III) ions that are incorporated into a well-isolated double-zigzag chain. The chain exhibits thermally induced reversible spin-crossover and light-induced excited spin-state trapping at the iron(II) sites. Single-chain magnet behaviour is actuated accompanying the synergy between light-induced excited spin-state trapping at the iron(II) sites and ferromagnetic interactions between the photoinduced high-spin iron(II) and low-spin iron(III) ions in the chain. The result provides a strategy to switch the bistable state of molecular nanomagnets using external stimuli such as light and heat, with the potential to erase and write information at a molecular level.

    DOI: 10.1038/ncomms3826

  • Computational prediction for singlet- and triplet-transition energies of charge-transfer compounds Reviewed

    Shuping Huang, Qisheng Zhang, Yoshihito Shiota, Tetsuya Nakagawa, Kazuhiro Kuwabara, Kazunari Yoshizawa, Chihaya Adachi

    Journal of Chemical Theory and Computation   9 ( 9 )   3872 - 3877   2013.9

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    Our work reveals a high dependence on charge-transfer (CT) amounts for the optimal Hartree-Fock percentage in the exchange-correlation functional of time-dependent density functional theory (TD-DFT) and the error of a vertical transition energy calculated by a given functional. Using these relations, the zero-zero transition energies of the first singlet and first triplet excited states of various CT compounds are accurately reproduced. 3CT and locally excited triplet (3LE) states are well distinguished and calculated independently. © 2013 American Chemical Society.

    DOI: 10.1021/ct400415r

  • Multi-Step Spin Crossover Accompanied by Symmetry Breaking in an Fe-III Complex: Crystallographic Evidence and DFT Studies Reviewed

    Zhao-Yang Li, Jing-Wei Dai, Yoshihito Shiota, Kazunari Yoshizawa, Shinji Kanegawa, Osamu Sato

    CHEMISTRY-A EUROPEAN JOURNAL   19 ( 39 )   12948 - 12952   2013.9

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    Spin doctor: A mononuclear ferric complex [Fe(H-5-Br-thsa)(5-Br-thsa)] ×H2O (1) (H2-5-Br-thsa=5-bromo-2-hydroxybenzylidene) hydrazinecarbothioamide) was synthesized and its magnetic properties and structure were investigated by DFT calculations. This complex shows unprecedented reversible, six/five-step spin-crossover behavior accompanied by symmetry breaking. More importantly, each step in the multi-step transition was successfully characterized by single-crystal X-ray diffraction. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

    DOI: 10.1002/chem.201302272

  • Complete Photochromic Structural Changes in Ruthenium(II)Diimine Complexes, Based on Control of the Excited States by Metalation Reviewed

    Takuya Sawaki, Tomoya Ishizuka, Masaki Kawano, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

    CHEMISTRY-A EUROPEAN JOURNAL   19 ( 27 )   8978 - 8990   2013.7

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    The thermal and photochemical reactions of a newly synthesized complex, [RuII(TPA)(tpphz)]2+ (1; TPA=tris(2-pyridylmethyl)amine, tpphz=tetrapyrido[3,2-a:2,3-c:3,2-h: 2,3-j]phenazine), and its derivatives have been investigated. Heating a solution of complex 1 (closed form) and its derivatives in MeCN caused the partial dissociation of one pyridylmethyl moiety of the TPA ligand and the resulting vacant site on the RuII center was occupied by a molecule of MeCN from the solvent to give a dissociated complex, [RuII(3-TPA)(tpphz)(MeCN)]2+ (1, open form), and its derivatives, respectively, in quantitative yields. The thermal dissociation reactions were investigated on the basis of kinetics analysis, which indicated that the reactions proceeded through a seven-coordinate transition state. Although the backwards reaction was induced by photoirradiation of the MLCT absorption bands, the photoreaction of complex 1 reached a photostationary state between complexes 1 and 1 and, hence, the recovery of complex 1 from complex 1 was 67%. Upon protonation of complex 1 at the vacant site of the tpphz ligand, the efficiency of the photoinduced recovery of complex 1+H+ from complex 1+H+ improved to 83%. In contrast, dinuclear -tpphz complexes 2 and 3, which contained the RuII(TPA)(tpphz) unit and either a RuII(bpy)2 or PdIICl2 moiety on the other coordination edge of the tpphz ligand, exhibited 100% photoconversion from their open forms into their closed forms (22 and 33). These results are the first examples of the complete photochromic structural change of a transition-metal complex, as represented by complete interconversion between its open and closed forms. Scrutinization by performing optical and electrochemical measurements allowed us to propose a rationale for how metal coordination at the vacant site of the tpphz ligand improves the efficiency of photoconversion from the open form into the closed form. It is essential to lower the energy level of the triplet metal-to-ligand charge-transfer excited state (3MLCT*) of the closed form relative to that of the triplet metal-centered excited state (3MC*) by metal coordination. This energy-level manipulation hinders the transition from the 3MLCT* state into the 3MC* state in the closed form to block the partial photodissociation of the TPA ligand.

    DOI: 10.1002/chem.201300437

  • Role of Tyrosine Residue in Methane Activation at the Dicopper Site of Particulate Methane Monooxygenase: A Density Functional Theory Study Reviewed

    Yoshihito Shiota, Gergely Juhasz, Kazunari Yoshizawa

    INORGANIC CHEMISTRY   52 ( 14 )   7907 - 7917   2013.7

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    Methane hydroxylation at the dinuclear copper site of particulate methane monooxygenase (pMMO) is studied by using density functional theory calculations. The electronic, structural, and reactivity properties of a possible dinuclear copper species (mu-oxo)(mu-hydroxo)(CuCuIII)-Cu-II are discussed with respect to the C-H bond activation of methane. We propose that the tyrosine residue in the second coordination sphere of the dicopper site donates an H atom to the mu-eta(2):eta(2)-peroxoCu(II)Cu(II) species and the resultant (mu-oxo)(mu-hydroxo)(CuCuIII)-Cu-II species can hydroxylate methane. This species for methane hydroxylation is more favorable in reactivity than the bis(p-oxo)(CuCuIII)-Cu-II species. The H-atom transfer or proton-coupled electron transfer from the tyrosine residue can reasonably induce the O-O bond dissociation of the mu-eta(2):eta(2)-peroxoCu(II)Cu(II) species to form the reactive (mu-oxo)(mu-hydroxo)(CuCuIII)-Cu-II species, which is expected to be an active species for the conversion of methane to methanol at the dicopper site of pMMO. The rate-determining step for the methane hydroxylation is the C H cleavage, which is in good agreement with experimental Km values reported so far.

    DOI: 10.1021/ic400417d

  • Heteronuclear (RuAgI)-Ag-II Complexes Having a Pyrroloquinolinequinone Derivative as a Bridging Ligand Reviewed

    Hiroumi Mitome, Tomoya Ishizuka, Yoshihiko Shiota, Kazunari Yoshizawa, Takahiko Kojima

    INORGANIC CHEMISTRY   52 ( 5 )   2274 - 2276   2013.3

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    Herein, we report the synthesis of a novel heterohexanuclear complex (1) of a heteroaromatic cofactor, pyrroloquinolinequinone (PQQ). The crystal structure of 1 was determined to reveal that two PQQ: bridged (RuAgI)-Ag-II units were linked by two [Ag-I(OTf)(2)](-) units (OTf = CF3SO3-). A solvent-bound (RuAgI)-Ag-II heterodinuclear complex (2) was formed from 1 in a coordinating solvent such as acetone to show an intense metal-to-ligand charge-transfer band at 709 nm.

    DOI: 10.1021/ic302617b

  • Thiophene-Fused Bisdehydro[12]annulene That Undergoes Transannular Alkyne Cycloaddition by Either Light or Heat Reviewed

    Aiko Fukazawa, Hiroya Oshima, Yoshihito Shiota, Shouya Takahashi, Kazunari Yoshizawa, Shigehiro Yamaguchi

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   135 ( 5 )   1731 - 1734   2013.2

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    A new bisdehydro[12]annulene derivative having a thiophene-fused structure has been synthesized. This highly twisted pi-conjugated macrocycle with two acetylene moieties in close proximity produces a [2+2]-type alkyne cycloadduct by either photoirradiation or mild heating without any transition metals. Theoretical calculations reveal that the thermal reaction proceeds through successive 8 pi and 4 pi electrocyclic reactions, while the photochemical reaction is an asynchronous concerted [2+2] cycloaddition. The fused structure with the less-aromatic thiophene ring is crucial for achieving this reaction. The cycloadduct, thiophene-fused biphenylene, has significant potential as a new polycyclic pi-scaffold for electronic applications.

    DOI: 10.1021/ja3126849

  • Multiply-fused porphyrins—effects of extended π-conjugation on the optical and electrochemical properties Reviewed International journal

    Tomoya Ishizuka, Yuta Saegusa, Yoshihito Shiota, Kazuhisa Ohtake, Kazunari Yoshizawa, Takahiko Kojima

    Chemical Communications   49 ( 53 )   5939 - 5941   2013.1

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    A novel quadruply-fused porphyrin has been synthesized with a facilely prepared precursor in a high yield. A detailed comparison of the physical properties of a series of fused porphyrins revealed remarkable effects of the ring fusion on lowering LUMO levels rather than HOMO levels.

    DOI: 10.1039/c3cc42831a

  • DFT study of the mechanism for methane hydroxylation by soluble methane monooxygenase (sMMO): Effects of oxidation state, spin state, and coordination number Reviewed International journal

    Shu Ping Huang, Yoshihito Shiota, Kazunari Yoshizawa

    Dalton Transactions   42 ( 4 )   1011 - 1023   2013.1

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    The exact structure of the active site of intermediate Q, the methane-oxidizing species of soluble methane monooxygenase (sMMO), and the reaction mechanism of Q with methane molecule are still not fully clear. To gain further insights into the structure and reaction mechanism, five diiron models of Q that differ in shape, oxidation state, spin state, and coordination number of the two iron centers are studied. Different mechanisms in different spin states were explored. Density functional theory (DFT) calculations show that FeIIIFeIV(μ-O)(μ-OH) is more reactive than Fe IV2(μ-O)2 in the oxygen-rich environment and that the reactivity of the active core of sMMO-Q is not enhanced by converting its oxo bridge into a terminal ligand. A four-coordinated diiron model is the most effective for methane hydroxylation. Both radical and non-radical intermediates are involved in the reactions for the four-coordinated diiron model.

    DOI: 10.1039/c2dt31304a

  • Substituent Effects in Thermal Reactions of a Silene with Silyl-Substituted Alkynes: A Theoretical Study Reviewed

    Hiromasa Tanaka, Yoshihito Shiota, Kazunori Hori, Akinobu Naka, Mitsuo Ishikawa, Kazunari Yoshizawa

    ORGANOMETALLICS   31 ( 13 )   4737 - 4747   2012.7

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    Thermal reactions of a silene derivative (Me3Si)(2)Si=C(OSiMe3)(t-Bu) (1) with silyl-substituted acetylenes, bis(trimethylsilyl)butadiyne, tert-butyldimethylsilylacetylene, and bis(trimethylsilyl)acetylene have been investigated with density functional theory calculations for the understanding of substituent effects in the reactivity of the silene. The first critical reaction step for determining the final product is the formation of a biradical intermediate from 1 and the acetylenes. A stepwise [2 + 2] cycloaddition via the biradical intermediate gives a silacyclobutene derivative, which is the precursor of the final product. The activation energy for this reaction step as well as thermodynamic stability of the biradical intermediate is governed by an interplay between geometric and electronic factors. The biradical intermediate is destabilized by steric hindrance between bulky substituents on 1 and acetylene, while it can be stabilized by delocalization of an unpaired electron in the acetylene moiety. Silacyclobutene derivatives undergo Si-C bond cleavage to give silabutadiene derivatives. The second critical reaction step is the attack of the OSiMe3 group on the silene Si atom in the silabutadienes. If the substituent on one of the acetylene C atoms does not easily migrate, the SiMe3 group of the OSiMe3 group rebounds to the silene C atom to form an oxasilacyclopentene derivative. If this substituent migrates easily, on the other hand, it migrates to the silene C atom with a simultaneous migration of the OSiMe3 group, resulting in the formation of an allene derivative.

    DOI: 10.1021/om300310g

  • Reversible electron transfer in a linear {Fe 2Co} trinuclear complex induced by thermal treatment and photoirraditaion Reviewed International journal

    Tao Liu, Da Peng Dong, Shinji Kanegawa, Soonchul Kang, Osamu Sato, Yoshihito Shiota, Kazunari Yoshizawa, Shinya Hayami, Shuo Wu, Cheng He, Chun Ying Duan

    Angewandte Chemie - International Edition   51 ( 18 )   4367 - 4370   2012.4

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    A light change: A linear cyanido-bridged Fe 2Co compound (see picture) exhibits a reversible, thermally induced cooperative charge transfer transition accompanying spin transition and polar-nonpolar transformation in the trinuclear cluster. The change in magnetic properties and polarity could also be induced by irradiation with light.

    DOI: 10.1002/anie.201201305

  • Proton-Coupled Electron Shuttling in a Covalently Linked Ruthenium-Copper Heterodinuclear Complex Reviewed

    Tomoya Ishizuka, Kengo Tobita, Yuichi Yano, Yoshihito Shiota, Kazunari Yoshizawa, Shunichi Fukuzumi, Takahiko Kojima

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   133 ( 46 )   18570 - 18573   2011.11

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    A heterodinuclear complex based on a Ru-II-TPA [TPA = tris(2-pyridylmethyl)amine] complex having a peripheral Cu-II (bpy)(2) (bpy = 2,2'-bipyridine) group bonded through an amide linkage displayed reversible intramolecular electron transfer between the Ru and Cu complex units that can be controlled by protonation and deprotonation of the bridging amide moiety.

    DOI: 10.1021/ja208141b

  • Corrigendum: Mechanistic Insights into Photochromic Behavior of a Ruthenium(II)-Pterin Complex Reviewed

    Tomoya Ishizuka, Takuya Sawaki, Soushi Miyazaki, Masaki Kawano, Yoshihito Shiota, Kazunari Yoshizawa, Shunichi Fukuzumi, Takahiko Kojima

    Chemistry - A European Journal   17 ( 36 )   9858   2011.8

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    Corrigendum: Mechanistic Insights into Photochromic Behavior of a Ruthenium(II)-Pterin Complex

    DOI: 10.1002/chem.201102220

  • Mechanistic Insights into Photochromic Behavior of a Ruthenium(II)-Pterin Complex (vol 17, pg 9848, 2011) Reviewed

    T. Ishizuka, T. Sawaki, S. Miyazaki, M. Kawano, Y. Shiota, K. Yoshizawa, S. Fukuzumi, T. Kojima

    CHEMISTRY-A EUROPEAN JOURNAL   17 ( 36 )   9857 - 9857   2011.8

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    DOI: 10.1002/chem.201102220

  • DFT study of the mechanism for methane hydroxylation by soluble methane monooxygenase Reviewed

    Shu-Ping Huang, Yoshihito Shiota, Kazunari Yoshizawa

    ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY   242   2011.8

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    The exact structure of the active site of intermediate Q, the methane-oxidizing species of soluble methane monooxygenase (sMMO), and the reaction mechanism of Q with methane molecule are still not fully clear. To gain further insights into the structure and reaction mechanism, we study different structure models of Q, including several new models not reported earlier, by performing broken-symmetry density functional theory calculations. Different reaction pathways of methane activated by Q with different structure models, including the radical and non-radical mechanism, are explored to evaluate which structure model is the most possible intermediate and the favorable catalytic mechanism. We expect our results to provide new insights into the catalytic oxidation of methane by sMMO and to promote the design of new catalysts.

  • Theoretical Study of Oxidation of Cyclohexane Diol to Adipic Anhydride by [Ru-IV(O)(tpa)(H2O)](2+) Complex (tpa = Tris(2-pyridylmethyl)amine) Reviewed

    Yoshihito Shiota, Jorge M. Herrera, Gergely Juhasz, Takafumi Abe, Shingo Ohzu, Tomoya Ishizuka, Takahiko Kojima, Kazunari Yoshizawa

    INORGANIC CHEMISTRY   50 ( 13 )   6200 - 6209   2011.7

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    The catalytic conversion of 1,2-cyclohexanediol to adipic anhydride by (RuO)-O-IV(tpa) (tpa tris(2-pyridylmethyl)amine) is discussed using density functional theory calculations. The whole reaction is divided into three steps: (1) formation of a-hydroxy cyclohexanone by dehydrogenation of cyclohexanediol, (2) formation of 1,2-cyclohexanedione by dehydrogenation of alpha-hydroxy cyclohexanone, and (3) formation of adipic anhydride by oxygenation of cyclohexanedione. In each step the two-electron oxidation is performed by (RuO)-O-IV(tpa) active species, which is reduced to bis-aqua Ru-II(tpa) complex. The Ru-II complex is reactivated using Ce(IV) and water as an oxygen source. There are two different pathways of the first two steps of the conversion depending on whether the direct H-atom abstraction occurs on a C H bond or on its adjacent oxygen O-H. In the first step, the C-H (O-H) bond dissociation occurs in TS1 (TS2-1) with an activation barrier of 21.4 (21.6) kcal/mol, which is followed by abstraction of another hydrogen pathways. The second process also bifurcates into two reaction pathways. TS3 (TS4 1) is leading to dissociation of the C-H (O-H) bond, and the activation barrier of TS3 (TS4-1) is 20.2 (20.7) kcal/mol. In the third step, oxo ligand attack on the carbonyl carbon and hydrogen migration from the water ligand occur via TS5 with an activation barrier of 17.4 kcal/mol leading to a stable tetrahedral intermediate in a triplet state. However, the slightly higher energy singlet state of this tetrahedral intermediate is unstable; therefore, a spin crossover spontaneously transforms the tetrahedral intermediate into a dione complex by a hydrogen rebound and a C C bond cleavage. Kinetic isotope effects (k(H)/k(D)) for the electronic processes of the C H bond dissociations calculated to be 4.9-7.4 at 300 K are in good agreement with experiment values of 2.8-9.0.

    DOI: 10.1021/ic200481n

  • Mechanistic Insights into Photochromic Behavior of a Ruthenium(II)-Pterin Complex Reviewed

    Tomoya Ishizuka, Takuya Sawaki, Soushi Miyazaki, Masaki Kawano, Yoshihito Shiota, Kazunari Yoshizawa, Shunichi Fukuzumi, Takahiko Kojima

    CHEMISTRY-A EUROPEAN JOURNAL   17 ( 24 )   6652 - 6662   2011.6

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    The pterin-coordinated ruthenium complex, [Ru-II(dmdmp)-(tpa)](+) (1) (Hdmdmp=N, N-dimethyl-6,7-dimethylpterin, tpa=tris(2-pyridyl-methyl)amine), undergoes photochromic isomerization efficiently. The isomeric complex (2) was fully characterized to reveal an apparent 1808 pseudorotation of the pterin ligand. Photoirradiation to the solution of 1 in acetone with incident light at 460 nm resulted in dissociation of one pyridylmethyl arm of the tpa ligand from the RuII center to give an intermediate complex, [Ru(dmdmp)(tpa)-(acetone)](2+) (I), accompanied by structural change and the coordination of a solvent molecule to occupy the vacant site. The quantum yield (phi) of this photoreaction was determined to be 0.87%. The subsequent thermal process from intermediate I affords an isomeric complex 2, as a result of the rotation of the dmdmp(2-) ligand and the recoordination of the pyridyl group through structural change. The thermal process obeyed first-order kinetics, and the rate constant at 298 K was determined to be 5.83 x 10(-5) s(-1). The activation parameters were determined to be Delta H-not equal = 81.8 kJmol(-1) and Delta S-not equal = -49.8 Jmol K-1 (1). The negative Delta S-not equal value indicates that this reaction involves a seven-coordinate complex in the transition state (i.e., an interchange associative mechanism). The most unique point of this reaction is that the recoordination of the photodissociated pyridylmethyl group occurs only from the direction to give isomer 2, without going back to starting complex 1, and thus the reaction proceeds with 100% conversion efficiency. Upon heating a solution of 2 in acetonitrile, isomer 2 turned back into starting complex 1. The backward reaction is highly dependent on the solvent: isomer 2 is quite stable and hard to return to 1 in acetone; however, 2 was converted to 1 smoothly by heating in acetonitrile. The activation parameters for the first-order process in acetonitrile were determined to be Delta H-not equal = 59.2 kJmol(-1) and Delta S not equal = -147.4 kJmol(-1)K(-1). The largely negative Delta S-not equal value suggests the involvement of a seven-coordinate species with the strongly coordinated acetonitrile molecule in the transition state. Thus, the strength of the coordination of the solvent molecule to the Ru-II center is a determinant factor in the photoisomerization of the Ru-II-pterin complex.

    DOI: 10.1002/chem.201003522

  • Theoretical Study on the Formation of Silacyclopropene from Acylsilane and Acetylene via Silene-to-Silylene Rearrangement Reviewed

    Hiromasa Tanaka, Yoshiyuki Kondo, Yoshihito Shiota, Akinobu Naka, Mitsuo Ishikawa, Kazunari Yoshizawa

    ORGANOMETALLICS   30 ( 11 )   3160 - 3167   2011.6

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    Density functional theory calculations have been performed for a proposal of possible mechanisms of the thermal reaction of an acylsilane, pivaloyltris-(trimethylsilyl)silane, and bis(trimethylsilyl)acetylene yielding a silacyclopropene, 1-[(tert-butyl)bis(trimethylsilyl)ethyl]-1-trimethylsiloxy-2,3-bis(trimethylsilyl)-1-silacycloprop-2-ene. Two reaction pathways in which two different silyl species play a role were considered based on analogous reactions of acylsilane and alkyne: (i) A silene (Si=C) intermediate derived from the acylsilane reacts with the acetylene to yield a silacyclobutene intermediate as a result of a stepwise [2 + 2] cycloaddition, and a ring-opening reaction of the silacyclobutene triggers the formation of the silacydopropene. (ii) The silene intermediate is rearranged to a silylene intermediate, and then [2 + 1] cycloaddition of the acetylene and the silylene gives the silacyclopropene. The high activation energy calculated for the [2 + 2] cycloaddition indicates that the silene would not react with the acetylene, which is consistent with the experimental result that no silacyclobutene intermediate was observed. On the other hand, the second reaction pathway involving the silene-to-silylene rearrangement and the [2 + 1] cycloaddition is more realistic from thermodynamic and kinetic points of view. All the calculated results strongly suggest that the silyl species reacting with bis(trimethylsilyl)acetylene is not silene but silylene.

    DOI: 10.1021/om2002393

  • Theoretical Study of the Mechanism of Valence Tautomerism in Cobalt Complexes Reviewed

    Daisuke Sato, Yoshihito Shiota, Gergely Juhasz, Kazunari Yoshizawa

    JOURNAL OF PHYSICAL CHEMISTRY A   114 ( 49 )   12928 - 12935   2010.12

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    Valence tautomerism is studied in the [CoII-HS(sq)(2)(bpy)]/[CoIII-LS(sq)(cat)(bp-y)] mononuclear cobalt complex by using DFT methods (HS, high spin; LS, low spin; cat, catecholate; sq, semiquinone; bpy, 2,2'-bipyridine). Calculations at the B3LYP* level of theory reproduce well the energy gap between the CoII-HS and CoIII-LS forms giving an energy gap of 4.4 kcal/mol, which is comparable to the experimental value of 8.9 kcal/mol. Potential energy surfaces and crossing seams of the electronic states of the doublet, quartet, and sextet spin states are calculated along minimum energy paths connecting the energy minima corresponding to the different spin states. The calculated minimum energy crossing points (MECPs) are located at 8.8 kcal/mol in the doublet/sextet surfaces, at 10.2 kcal/mol in the doublet/quartet surfaces, and at 8.4 kcal/mol in the quartet/sextet surfaces relative to the doublet ground state. Considering the energy of the three spin states and the crossing points, the one-step relaxation mechanism between the CoII-HS and CoIII-LS forms is the most probable. This research shows that mapping MECPs can be a useful strategy to analyze the potential energy surfaces of systems with complex deformation modes.

    DOI: 10.1021/jp107391x

  • A low-spin ruthenium(IV)-oxo complex: Does the spin state have an impact on the reactivity? Reviewed International journal

    Takahiko Kojima, Yuichirou Hirai, Tomoya Ishizuka, Yoshihito Shiota, Kazunari Yoshizawa, Kenichiro Ikemura, Takashi Ogura, Shunichi Fukuzumi

    Angewandte Chemie - International Edition   49 ( 45 )   8449 - 8453   2010.11

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    Spin doesn't matter: A ruthenium(II)-aqua complex bearing a pentadentate pyridylamine with a carboxylate group as a ligand affords a seven-coordinate low-spin (S=0) ruthenium(IV)-oxo complex (see structure) by oxidation through proton-coupled electron transfer. Comparison of the reactivity of the low-spin and an intermediate-spin (S=1) RuIV-oxo complexes revealed that the spin state does not affect the reactivity of catalytic oxidation of organic compounds.

    DOI: 10.1002/anie.201002733

  • Theoretical Study of Thermal Spin Transition between the Singlet State and the Quintet State in the [Fe(2-picolylamine)(3)](2+) Spin Crossover System Reviewed

    Yoshihito Shiota, Daisuke Sato, Gergely Juhasz, Kazunari Yoshizawa

    JOURNAL OF PHYSICAL CHEMISTRY A   114 ( 18 )   5862 - 5869   2010.5

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    The spin transition between the low-spin singlet state and the high-spin quintet state in the [Fe(2-pic)(3)](2+) (2-pic: 2-picolylamine) complex is studied by using density functional theory (DFT) calculations. After careful comparison of density functionals BLYP, B3LYP, and B3LYP* (which has 15% Hartree-Fock exchange compared with 20% for B3LYP), we concluded that the spin-state splitting can be accurately reproduced by using the B3LYP* functional. The potential energy surfaces along minimum energy pathways of the three spin states were calculated at the B3LYP*/6-311+G** level of theory to find minimum energy crossing points (MECPs). The MECPs between the singlet and quintet states (SQ(M)) were found (E-SQ = 6.8 kcal/mol), as well as the MECPs between the triplet and singlet states (STM, E-ST = 12.9 kcal/mol) and the triplet and quintet states (TQ(M), E-TQ = 12.8 kcal/mol). Although the distortion leading to SQ(M) from the singlet equilibrium geometry is mainly a symmetric expansion of the Fe-N bonds, the distortions leading to STM and SQ(M) are asymmetric. Normal mode analysis demonstrates that these geometrical distortions contain a combination of several low-frequency normal modes, and therefore, these modes play a significant role in the intersystem crossing via the crossing seam.

    DOI: 10.1021/jp9122002

  • Synthesis and Characterization of Ruthenium(II)-Pyridylamine Complexes with Catechol Pendants as Metal Binding Sites Reviewed

    Takahiko Kojima, Norihisa Hirasa, Daisuke Noguchi, Tomoya Ishizuka, Soushi Miyazaki, Yoshihito Shiota, Kazunari Yoshizawa, Shunichi Fukuzumi

    INORGANIC CHEMISTRY   49 ( 8 )   3737 - 3745   2010.4

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    A novel tris(2-pyridylmethyl)amine (TPA) derivate having two catechol moieties linked by amide linkages at the 6-positions of two pyridyl groups was synthesized. The ligand, N,N-bis[6-{3,4-(dihydroxy)benzamide}-2-pyridyl-methyl]-N-(2-pyridylmethyl)amine (Cat(2)-TPA; L2), and its precursor, N,N-bis[6-{3,4-bis(benzyloxy)-benzamide}-2-pyridylmethyl]-N-(2-pyridylmethyl)-amine ((Bn(2)Cat)(2)-TPA; L1), formed stable ruthenium(II) complexes, [RuCl(L2)]PF(6) (2) and [RuCl(L1)]PF(6) (1), respectively. The crystal structure of [RuCl(L2)]Cl (2') was determined by X-ray crystallography to show two isomers in terms of the orientation of one catechol moiety. In complex 2, the ligand bearing catechols acts as a pentadentate ligand involving coordination of one of the amide oxygen atoms in addition to that of the tetradentate TPA moiety and two metal-free catechol moieties as metal-binding sites. The coordination of L2 results in the preorganization of the two catechols to converge them to undergo intramolecular pi-pi interactions. The (1)H NMR spectrum of 2 in DMSO-d(6) revealed that only one isomer was present in the solution. This selective formation could be ascribed to the formation of an intramolecular hydrogen-bonding network among the hydroxyl groups of the catechol moieties, as suggested by X-ray analysis. This intramolecular hydrogen bonding could differentiate the pK(a) values of the hydroxy groups of the catechol moieties into three kinds, as indicated by spectroscopic titration with tetramethylammonium hydroxide (TMAOH) in DMF. The complexation of 2 with other metal ions was also examined. The reaction of 2 with [Cu(NO(3))(2)(TMEDA)] (TMEDA = N,N,N',N'-tetramethylethylenediamine) in methanol allowed us to observe the selective formation of a binuclear complex, [RuCl(L2(2-)){Cu(TMEDA)}]PF(6) (3), which was characterized by ESI-MS, UV-vis, and ESR spectroscopies. Its ESR spectrum in methanol suggested that the coordination of the Cu(II)-TMEDA unit to the converged catechol moieties would be different from conventional kappa(2)-O,O':eta(2)-coordination: it exhibits a novel bridging coordination mode, bis-kappa(1)-O:eta(1)-coordination, to form the binuclear Ru(II)-Cu(II) complex.

    DOI: 10.1021/ic902070q

  • Metal-Ligand Cooperation in H-2 Production and H2O Decomposition on a Ru(II) PNN Complex: The Role of Ligand Dearomatization-Aromatization Reviewed

    Jun Li, Yoshihito Shiota, Kazunari Yoshizawa

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   131 ( 38 )   13584 - +   2009.9

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    The molecular mechanism for H-2 production and H2O decomposition on an aromatic Ru(II) PNN complex developed by Milstein and co-workers has been elucidated by detailed density functional theory calculations. The rate-determining step is heterolytic coupling of the hydride with a proton transferred from the PNN ligand, which leads to the formation of H-2. The metal center and the PNN ligand, which can be dearomatized and aromatized again, play active and synergistic roles in H-2 production and the succeeding H2O decomposition. Formation of the cis-dihydroxo complex as the main final product is a result of thermodynamic control.

    DOI: 10.1021/ja905073s

  • DFT study on N2 activation by a hydride-bridged diniobium complex. N≡N Bond cleavage accompanied by H2 evolution Reviewed

    Tanaka H, Shiota Y, Matsuo T, Kawaguchi H, Yoshizawa K

    Inorganic Chemistry   48 ( 8 )   3875 - 3881   2009.4

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    DFT Study on N-2 Activation by a Hydride-Bridged Diniobium Complex. N N Bond Cleavage Accompanied by H-2 Evolution
    Density functional theory (DFT) calculations have been performed for the investigation of a plausible mechanism of the triple bond cleavage of N-2 in a diniobium complex supported by tridentate aryloxide ligands, {Nb-V(mu-N)(2)Nb-V}(2-22) With the assumption of a tetrakis(mu-hydrido)diniobium complex {Nb-IV(mu-H)(4)Nb-IV}(2-) as an initial complex, the N N cleavage on the Nb-2 core proceeds in four steps. Dinitrogen is coordinated to the {Nb-III(mu-H)(2)Nb-III} core in a side-on/end-on manner, accompanied by the reductive elimination of H-2. The N N bond of dinitrogen is activated up to a single bond (formally N-2(4-)) by the two Nb(III) atoms, once it is bound to the Nb-2 core. Two electrons are prepared for the cleavage of the N-N single bond through the mu-H migration to an N atom, leading to the formation of an Nb-Nb bond. The N-N bond is then dissociated by the two electrons that are shared between the two Nb atoms. Finally, {Nb(mu-N)(2)Nb}(2-) is generated after H-2 elimination in which the N-bonded H atom is coupled with the remaining mu-H atom. The final H-2 elimination is calculated to be the rate-determining step.

    DOI: 10.1021/ic802377p

  • Nickel(II), Palladium(II), and Platinum(II) η3-Allyl Complexes Bearing a Bidentate Titanium(IV) Phosphinoamide Ligand: A Ti←M2 Dative Bond Enhances the Electrophilieity of the π-Allyl Reviewed

    Tsutsumi H, Sunada Y, Shiota Y, Yoshizawa K, Nagashima H

    Organometallics   28 ( 7 )   1988 - 1991   2009.4

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    Nickel(II), Palladium(II), and Platinum(II) eta(3)-Allyl Complexes Bearing a Bidentate Titanium(IV) Phosphinoamide Ligand: A Ti <- M-2 Dative Bond Enhances the Electrophilicity of the pi-Allyl Moiety
    Three Ti-M-2 (M-2=Ni, Pd, Pt) heterobimetallic complexes, [(eta(3-)methallyl) M-2((Ph2PNBu)-Bu-t)(2)TiCl2](OTF), were synthesized in which a Ti-IV <- M-2 interaction was suggested by crystallography and DFT calculations. The Ti-IV <- M-2 interaction enhanced electrophilicity of the eta(3)-methallyl ligand of M-2, leading to high reactivity of the eta(3)-methallyl moiety with Et2NH compared with that of the dppp analogue.

    DOI: 10.1021/om8011085

  • Comparison of the reactivity of bis(μ-oxo)CuIICu III and CuIIICuIII species to methane Reviewed

    Shiota Y, Yoshizawa K

    Inorganic Chemistry   48 ( 3 )   838 - 845   2009.2

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    Comparison of the Reactivity of Bis(mu-oxo)(CuCuIII)-Cu-II and (CuCuIII)-Cu-III Species to Methane
    Methane hydroxylation at the Binuclear copper site of particulate methane monooxygenase (AMMO) is studied by using density functional theory (DFT) calculations. The electronic and structural properties of the dinuclear copper species of bis(mu-oxo)(CuCuIII)-Cu-II and (CuCuIII)-Cu-III are discussed with respect to the C-H bond activation of methane. The bis(mu-oxo)(CuCuIII)-Cu-II species is highly reactive and considered to be an active species for the conversion of methane to methanol by pMMO, whereas the bis(mu-oxo)(CuCuIII)-Cu-III species is unable to react with methane as it is. If a Cu-O bond of the bis(mu-oxo)(CuCuIII)-Cu-III species is cleaved, the resultant (CuCuIII)-Cu-III species, in which only one oxo ligand bridges the two copper ions, can activate methane. However, its energetics for methane hydroxylation is less favorable than that by the bis(mu-oxo)(CuCuIII)-Cu-II species. The DFT calculations show that the bis(mu-oxo)(CuCuIII)-Cu-II species is more effective for the activation of methane than the bis(mu-oxo)(CuCuIII)-Cu-III species. The reactive bis(mu-oxo)(CuCuIII)-Cu-II species can be created either from the electron injection to the bis(mu-oxo)(CuCuIII)-Cu-III species or from the O-O bond cleavage in the mu-eta(1):eta(2)-peroxoCu(I)Cu(II) species.

    DOI: 10.1021/ic8003933

  • Quantum Chemical Approach to the Mechanism for the Biological Conversion of Tyrosine to Dopaquinone Reviewed

    Toshinori Inoue, Yoshihito Shiota, Kazunari Yoshizawa

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   130 ( 50 )   16890 - 16897   2008.12

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    Tyrosinase catalyzes the biological conversion of tyrosine to dopaquinone with dioxygen at the dinuclear copper active site under physiological conditions. On the basis of the recent X-ray crystal structural analysis of tyrosinase (J BioL Chem. 2006, 281, 8981), a possible mechanism for the catalytic cycle of tyrosinase is proposed by using quantum mechanical/molecular mechanical calculations, which can reasonably take effects of surrounding amino-acid residues, hydrogen bonding, and protein environment into account. The (mu-eta(2):eta(2)-peroxo)dicopper(II) species plays a role in a series of elementary processes mediated by the dicopper species of tyrosinase. A stable phenoxyl radical is involved in the reaction pathway. The catalysis has five steps of proton transfer from the phenolic O-H bond to the dioxygen moiety, O-O bond dissociation of the hydroperoxo species, C-O bond formation at an ortho position of the benzene ring, proton abstraction and migration mediated by His54, and quinone formation. The energy profile of the calculated reaction pathway is reasonable in energy as biological reactions that occur under physiological conditions. Detailed analyses of the energy profile demonstrate that the O-O bond dissociation is the rate-determining step. The activation energy for the O-O bond dissociation at the dicopper site is computed to be 14.9 kcal/mol, which is in good agreement with a measured kinetic constant. As proposed recently, the His54 residue, which is flexible because it is located in a loop structure in the protein, would play a role as a general base in the proton abstraction and migration in the final stages of the reaction to produce dopaquinone.

    DOI: 10.1021/ja802618s

  • Ruthenium-catalyzed selective and efficient oxygenation of hydrocarbons with water as an oxygen source Invited Reviewed International journal

    Yuichirou Hirai, Takahiko Kojima, Yasuhisa Mizutani, Yoshihito Shiota, Kazunari Yoshizawa, Shunichi Fukuzumi

    Angewandte Chemie - International Edition   47 ( 31 )   5772 - 5776   2008.7

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    (Chemical Equation Presented) Water is not only the solvent but also the sole oxygen source in the smooth and efficient oxidation of organic compounds catalyzed by a RuII-pyridylamine-aqua complex with CeIV as the oxidant. An intermediate-spin RuIV-oxo complex is formed as the reactive species (see scheme; Sub = substrate). This catalytic system is durable and able to gain high turnover numbers for various substrates.

    DOI: 10.1002/anie.200801170

  • Synthesis and characterization of novel ferrocene-containing pyridylamine ligands and their ruthenium(II) complexes: Electronic communication through hydrogen-bonded amide linkage Reviewed

    Takahiko Kojima, Daisuke Noguchi, Tomoko Nakayama, Yuji Inagaki, Yoshihito Shiota, Kazunari Yoshizawa, Kei Ohkubo, Shunichi Fulkuzumi

    INORGANIC CHEMISTRY   47 ( 3 )   886 - 895   2008.2

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    Tris(2-pyridylmethyl)amine (TPA) derivatives with one or two ferrocenoylamide moieties at the 6-position of one or two pyridine rings of TPA were synthesized. The compounds, N-(6-ferrocenoylamide-2-pyridylmethyl)-NN-bis(2-pyridylmethyl)amine (Fc-.TPA; L1) and N,N-bis(6-ferrocenoylamide-2-pyridylmethyl)-N-(2-pyridylmethyl)amine (Fc(2)-TPA; L2), were characterized by spectroscopic methods, cyclic voltammetry, and X-ray crystallography. Their Ru(II) complexes were also prepared and characterized by spectroscopic methods, cyclic voltammetry, and X-ray crystallography. [RuCl(L1)(DMSO)]PF6 (1) that contains S-bound climethyl sulf oxide, (DMSO) as a ligand and an uncoordinated ferrocenoylamide moiety exhibited two redox waves at 0.23 and 0.77 V (vs ferrocene/ferrocenium ion as 0 V), due to Fc/Fc(+) and Ru(II)/Ru(III) redox couples, respectively. [RuCl(L2)]PF6 (2) that contains both coordinated and uncoordinated amide moieties showed two redox waves that were observed at 0.27 V (two electrons) and 0.46 V (one electron), assignable to Ru(II)/Ru(III) redox couples overlapped with the uncoordinated Fc/Fc(+) redox couple and the coordinated Fc/Fc+, respectively. In contrast to 2, an acetonitrile complex, [Ru(L2)(CH3CN)](PF6)(2) (3), exhibited three redox couples at 0.26 and 0.37 V for two kinds of Fc/Fc(+) couples, and 0.83 V for the Ru(II)/Ru(III) couple (vs ferrocene/ferrocenium ion as 0 V). In this complex, the redox potentials of the coordinated and the uncoordinated Fc-amide moieties were discriminated in the range of 0.11 V. Chemical two-electron oxidation of 1 gave [(RuCl)-Cl-III(L1(+))(DMSO)](3+) to generate a ferromagnetically coupled triplet state (S = 1) with J = 13.7 cm(-1) (H = -JS(1)S(2)) which was estimated by its variable-temperature electron spin resonance (ESR) spectra in CH3CN. The electron spins at the Ru(III) center and the Fe(III) center are ferromagnetically coupled via an amide linkage. In the case of 2, its two-electron oxidation gave the same ESR spectrum, which indicates formation of a similar triplet state. Such electronic communication may occur via the amide linkage forming the intramolecular hydrogen bonding.

    DOI: 10.1021/ic7016038

  • Theoretical analysis of the reaction mechanism of biotin carboxylase Reviewed

    Yuko Ito, Hiroki Kondo, Yoshihito Shiota, Kazunari Yoshizawa

    JOURNAL OF CHEMICAL THEORY AND COMPUTATION   4 ( 2 )   366 - 374   2008.2

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    A computational approach is taken to clarify the reaction mechanism of biotin carboxylase (BC) by using the B3LYP density functional method. The overall reaction of BC is supposed to consist of two steps: in the first step, carboxyphosphate (CP) is generated from bicarbonate and ATP, and it is subject to nucleophilic attack on its carboxyl group by biotin to form carboxybiotin in the second step. The activation energies for the transition states of the first and second steps are computed to be 46.6 and 7.9 kcal/mol, respectively, demonstrating that the first step limits the overall reaction of BC. In the second step, the ureido moiety of biotin undergoes enolization with the aid of general acid-base catalysis by CID, followed by collapse of CP into CO2 and phosphate. The resulting bent CO2 is highly labile and condenses quickly with enolic biotin to give carboxybiotin. Implicit in this scheme as they are, ingenious proton movements between the two substrates, CP and biotin, dictate all of the succeeding chemical events.

    DOI: 10.1021/ct700260f

  • DFT analysis of cubane-type FeIr3S4 clusters. Dinitrogen binding and activation at the tetrahedral Fe site Reviewed

    Pawel M. Kozlowski, Yoshihito Shiota, Satomi Gomita, Hidetake Seino, Yasushi Mizobe, Kazunari Yoshizawa

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN   80 ( 12 )   2323 - 2328   2007.12

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    The electronic and structural properties of the cubane-type mixed-metal sulfido clusters with a FeIr3S4 core and possible dinitrogen binding and activation were analyzed by density functional theory (DFT) calculations. Five different charges of the cluster and manifold of the electronic states were investigated. For each charge under consideration (+2, +1, 0, -1, -2) systematic analysis of structural and electronic properties was carried out. The DFT calculations show that both Fe - N and N N bond lengths correlate with the total charge of the cluster. The length of the Fe - N bond decreased, whereas the N N bond length increased with the number of added electrons. However, only noticeable elongation of the N N bond was observed when the charge of the cluster became negative. Similar analysis was extended to species that have protonated dinitrogen bond. The results obtained from the DFT analysis are useful in considering the principles of the reduction of dinitrogen to ammonia at a single metal center.

    DOI: 10.1246/bcsj.80.2323

  • Conversion of methane to methanol at the mononuclear and dinuclear copper sites of particulate methane monooxygenase (pMMO): A DFT and QM/MM study Reviewed

    Kazunari Yoshizawa, Yoshihito Shiota

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   128 ( 30 )   9873 - 9881   2006.8

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    Methane hydroxylation at the mononuclear and dinuclear copper sites of pMMO is discussed using quantum mechanical and QM/MM calculations. Possible mechanisms are proposed with respect to the formation of reactive copper-oxo and how they activate methane. Dioxygen is incorporated into the Cu(I) species to give a Cu(II)- superoxo species, followed by an H-atom transfer from a tyrosine residue near the monocopper active site. A resultant CuII- hydroperoxo species is next transformed into a Cu(III)-oxo species and a water molecule by the abstraction of an H-atom from another tyrosine residue. This process is accessible in energy under physiological conditions. Dioxygen is also incorporated into the dicopper site to form a (mu-eta(2):eta(2)-peroxo)dicopper species, which is then transformed into a bis(mu-oxo) dicopper species. The formation of this species is more favorable in energy than that of the monocopper- oxo species. The reactivity of the Cu(III)-oxo species is sufficient for the conversion of methane to methanol if it is formed in the protein environment. Since the sigma* orbital localized in the Cu-O bond region is singly occupied in the triplet state, this orbital plays a role in the homolytic cleavage of a C-H bond of methane. The reactivity of the bis(mu-oxo) dicopper species is also sufficient for the conversion of methane to methanol. The mixed-valent bis(mu-oxo)Cu(II)Cu(III) species is reactive to methane because the amplitude of the sigma* singly occupied MO localized on the bridging oxo moieties plays an essential role in C-H activation.

    DOI: 10.1021/ja061604r

  • QM/MM study on the catalytic mechanism of benzene hydroxylation over Fe-ZSM-5 Reviewed

    Y Shiota, K Suzuki, K Yoshizawa

    ORGANOMETALLICS   25 ( 13 )   3118 - 3123   2006.6

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    The direct conversion of benzene to phenol over Fe-ZSM-5 zeolite is investigated using quantum mechanical/molecular mechanical (QM/MM) calculations on a large model consisting of 683 SiO2 units ( 2084 atoms). The active-site model for benzene hydroxylation involves a mononuclear iron-oxo species (Fe-III=O) located at the ion-exchangeable Al site of ZSM-5 zeolite. The proposed catalytic cycle is partitioned into four steps: (i) H atom abstraction, (ii) O atom insertion, (iii) phenyl migration, and (iv) phenol release. The decomposition of nitrous oxide plays an important role in the formation of the iron-oxo species and in the avoidance of the unstable Fe-I state at the active site. The catalytic reaction occurs on the sextet and quartet potential energy surfaces. The quartet state plays a major role in the course of the reaction, whereas the sextet state lies lower in energy in the entrance channel and in the final stages of the reaction. The QM/MM calculations show that the nanopores of the zeolite framework would decrease the activation barriers in the transition states involved in the reaction pathway and accelerate the exchange of phenol and benzene in the final stages of the reaction. The environmental effect from the zeolite framework promotes the conversion of benzene to phenol.

    DOI: 10.1021/om0509591

  • Catalytic mechanism of dopamine β-monooxygenase mediated by Cu(III)-oxo Reviewed

    Yoshizawa K, Kihara N, Kamachi T, Shiota Y

    Inorganic Chemistry   45 ( 7 )   3034 - 3041   2006.4

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    Catalytic mechanism of dopamine, beta-monooxygenase mediated by Cu(III)-Oxo
    Mechanisms of dopamine hydroxylation by the Cu(II)-superoxo species and the Cu(III)-oxo species of dopamine beta-monooxygenase (DBM) are discussed using QM/MM calculations for a whole-enzyme model of 4700 atoms. A calculated activation barrier for the hydrogen-atom abstraction by the Cu(II)-superoxo species is 23.1 kcal/mol, while that of the Cu(III)-oxo, which can be viewed as Cu(II)-O-center dot, is 5.4 kcal/mol. Energies of the optimized radical intermediate in the superoxo- and oxo-mediated pathways are 18.4 and -14.2 kcal/mol, relative to the corresponding reactant complexes, respectively. These results demonstrate that the Cu(Ill)-oxo species can better mediate dopamine hydroxylation in the protein environment of DBM. The side chains of three amino acid residues (His415, His417, and Met490) coordinate to the Cu-B atom, one of the copper sites in the catalytic core that plays a role for the catalytic function. The hydrogen-bonding network between dopamine and the three amino acid residues (Glu268, Glu369, and Tyr494) plays an essential role in substrate binding and the stereospecific hydroxylation of dopamine to norepinephrine. The dopamine hydroxylation by the Cu(Ill)-oxo species is a downhill and lower-barrier process toward the product direction with the aid of the protein environment of DBM. This enzyme is likely to use the high reactivity of the Cu(Ill)-oxo species to activate the benzylic C-H bond of dopamine; the enzymatic reaction can be explained by the so-called oxygen rebound mechanism.

    DOI: 10.1021/ic0521168

  • DFT calculations of cubane-type Mo2Ru2S4 clusters. Stability of a possible dinitrogen cluster and an isolable acetonitrile cluster Reviewed

    K Yoshizawa, N Kihara, Y Shiota, H Seino, Y Mizobe

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN   79 ( 1 )   53 - 58   2006.1

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    The electronic properties of cubane-type mixed-metal sulfido clusters with an Mo(V)(2)Ru(II)(2)S-4 core and possible dinitrogen activation on it are described from DFT computations. The cluster [(CpRu)(2){MoCl2(MeCN)}(2)(mu(3)-S)(4)] (Cp = eta(5)-C5H5), whose Cp* analogue (Cp* = eta(5)-C5Me5) was isolated and fully characterized by X-ray crystallographic analysis, has a closed-shell singlet ground state. Upon release of the acetonitrile ligands, the ground state remains in a closed-shell singlet state, the corresponding open-shell singlet and triplet states lying 2 kcal mol(-1) above the closed-shell singlet state. Dinitrogen can hardly coordinate to this neutral [(CpRu)(2)(MoCl2)(2)(mu(3)-S)(4)] cluster. However, upon reduction by two electrons the binding energy for two N-2 molecules to the resultant anionic cluster [(CpRu)(2){MoCl2(N-2)}(2)(mu(3)-S)(4)](2-) increases to 4 kcal mol(-1). This interaction, which still seems too weak to become isolable, is analyzed in terms of molecular orbitals to increase our understanding of dinitrogen activation by synthetic systems. The HOMO of [(CpRu)(2)(MoCl2)(2)(mu(3)-S)(4)](2-) is pointing toward missing ligands and can interact effectively with the pi(g)* orbitals of dinitrogen. This orbital might play a role in the binding of dinitrogen.

    DOI: 10.1246/bcsj.79.53

  • Synthesis and characterization of ruthenium(II)-nitrile complexes with bisamide-tpa ligands (tpa = tris(2-pyridylmethyl)amine) Reviewed

    T Kojima, KI Hayashi, Y Shiota, Y Tachi, Y Naruta, T Suzuki, K Uezu, K Yoshizawa

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN   78 ( 12 )   2152 - 2158   2005.12

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    Ruthenium(II)-acetonitrile complexes having pentadentate tris(2-pyridylmethyl)amine (tpa) derivatives with coordinated amide CO groups were prepared and characterized by various spectroscopic methods, electrochemical measurements, and DFT calculations. The acetonitrile ligand was indicated to tightly bind to the ruthenium(II) center in an eta(1)-N fashion. The Mulliken charge distribution, obtained by a calculation, indicated that the ruthenium(II)-nitrile bond is more covalent than other coordination bonds of the tpa moiety. The redox potentials of Ru centers and the chemical shifts of methyl groups of the acetonitrile ligands exhibited a linear relationship, indicating that electron density of the Ru center controls that of the acetonitrile ligand. Those complexes showed fluxional behavior in CD3CN solutions to exhibit one mode of thermal motion; it also altered the symmetry of the complexes.

    DOI: 10.1246/bcsj.78.2152

  • Mechanism for the direct oxidation of benzene to phenol by FeO+ Reviewed

    Y Shiota, K Suzuki, K Yoshizawa

    ORGANOMETALLICS   24 ( 14 )   3532 - 3538   2005.7

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    Reaction pathways and energetics for the conversion of benzene to phenol by FeO+ in the gas phase are discussed using density functional theory calculations at the B3LYP/6-311+G** level of theory. Three reaction pathways are available for this reaction. The first one is a nonradical mechanism to form a hydroxo intermediate, HO-Fe+-C6H5 via H atom abstraction with a four-centered transition state, which occurs at a coordinatively unsaturated metal center. The second one is a radical mechanism to form a phenyl radical and an FeOH fragment as an intermediate via H-atom abstraction with a linear C-H-O transition state. The third one is an oxygen-insertion mechanism to form an arenium intermediate via electrophilic aromatic addition. The energies of the transition states with respect to H-atom abstraction (relative to the dissociation limit) increase in the order of the first, third, and second mechanisms. A detailed analysis of the potential energy surfaces shows that the first mechanism is most likely to occur when the metal active site is coordinatively unsaturated. The second mechanism is energetically unlikely. The third pathway is branched into cyclohexadienone and benzene oxide, which are formed by a 1,2-hydrogen migration find a ring closure in the arenium intermediate, respectively. Cyclohexadienone can play a role as an intermediate when the metal active site is coordinatively saturated, whereas the formation of benzene oxide is unlikely to occur under ambient conditions because of its extremely high energy.

    DOI: 10.1021/om050136b

  • Computational exploration of the catalytic mechanism of dopamine β-monooxygenase: Modeling of its mononuclear copper active sites Reviewed

    Kamachi T, Kihara N, Shiota Y, Yoshizawa K

    Inorganic Chemistry   44 ( 12 )   4226 - 4236   2005.6

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    Computational exploration of the catalytic mechanism of dopamine beta-monooxygenase: Modeling of its mononuclear copper active sites
    Dopamine hydroxylation by the copper-superoxo, -hydroperoxo, and -oxo species of dopamine P-monooxygenase (DBM) is investigated using theoretical calculations to identify the active species in its reaction and to reveal the key functions of the surrounding amino acid residues in substrate binding. A 3D model of rat DBM is constructed by homology modeling using the crystal structure of peptidylglycine alpha-hydroxylating monooxygenase (PHM) with a high sequence identity of 30% as a template. In the constructed 3D model, the CuA site in domain 1 is coordinated by three histidine residues, His265, His266, and His336, while the CuB site in domain 2 is coordinated by two histidine residues, His415 and His417, and by a methionine residue, Met490. The three Glu268, Glu369, and Tyr494 residues are suggested to play an important role in the substrate binding at the active site of DBM to enable the stereospecific hydrogen-atom abstraction. Quantum mechanical/molecular mechanical (OM/MM) calculations are performed to determine the structure of the copper-superoxo, -hydroperoxo, and -oxo species in the whole-enzyme model with about 4700 atoms. The reactivity of the three oxidants is evaluated in terms of density-functional-theory calculations with small models extracted from the OM region of the whole-enzyme model.

    DOI: 10.1021/ic048477p

  • QM/MM study of the mononuclear non-heme iron active site of phenylalanine hydroxylase Reviewed

    Y Shiota, K Yoshizawa

    JOURNAL OF PHYSICAL CHEMISTRY B   108 ( 44 )   17226 - 17237   2004.11

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    The reaction pathway and energetics for the hydroxylation of L-phenylalanine to L-tyrosine are analyzed by a combined quantum mechanical/molecular mechanical (QM/MM) method and a conventional QM method. A reasonable model for the oxygen species responsible for the catalytic reactivity of phenylalanine hydroxylase (PAH) is proposed. The active site model of PAH is a catalytic domain model (including 5176 atoms), which is a truncated form of PAH lacking the N-terminal regulatory and C-terminal tetramerization domains. This model can reasonably treat the protein environment via nonbonding interactions between the QM (iron active site and substrate) and MM (catalytic domain) regions. The QM region involves an iron-oxo species (Fe-IV= O), side-chain ligands of His285, His290, and Glu330, and two water molecules at the binding site of the catalytic active center. Possible reaction pathways are discussed. One is a reaction initiated by a C-H bond cleavage via an H-atom abstraction, followed by a C-O bond formation leading to an L-tyrosine complex. Another is a reaction initiated by an oxygen insertion via electrophilic aromatic addition, followed by the 1,2 hydride shift leading to the keto form (2,4-cyclohexadienone) of the L-tyrosine complex. The structures of the reactant complex, the radical intermediate, and the product complex with the catalytic domain are described. QM/MM calculations tell us that the substrate-binding site in PAH is located at Pro279 and Val379. As a result of QM calculations, the activation energies for the C-H cleavage step and the C-O bond formation in the first mechanism are 24.6 and 9.2 kcal/mol, respectively, while the activation energy for the 1,2 hydride shift in the second one is 9.0 kcal/mol relative to the arenium intermediate. Thus, the QM calculations suggest that the oxygen insertion mechanism is energetically more favorable.

    DOI: 10.1021/jp048001r

  • Theoretical study of thermal isomerization of silacyclobutene to cyclopropene Reviewed

    Y Shiota, M Yasunaga, A Naka, M Ishikawa, K Yoshizawa

    ORGANOMETALLICS   23 ( 20 )   4744 - 4749   2004.9

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    The reaction pathway and energetics for the conversion of silacyclobutene to cyclopropene, which plays a role as an intermediate in complicated thermal reactions of silacyclobutene, are discussed using B3LYP/6-31+G(d,p) level calculations. There are two reaction pathways in its thermal isomerization: (1) cyclopropene is formed via silabutadiene that is formed by the ring opening of silacyclobutene in a conrotatory process; (2) cyclopropene is directly formed by a 1,2-siloxyl shift in silacyclobutene. The first mechanism involves two-step processes. Two kinds of ring-opening reactions based on the Woodward-Hoffmann rule result in the formation of cis- and trans-silabutadienes that involve an Si=C double bond. Calculated activation barriers for the formation of cis- and trans-silabutadienes are 36.5 and 21.8 kcal/mol, respectively. Thus, the trans form is energetically more favorable than the cis form in this ring-opening step. This result is in good agreement with experimental observations that the methanol adduct derived from the trans form is detected in the presence of methanol. However, the next transition state with respect to a 1,4-siloxyl shift takes place only in the cis form, due to the orientation of the siloxyl group. A calculated activation barrier for the 1,4-siloxyl shift in cis-silabutadiene is 17.2 kcal/mol. Thus, the first step is the rate-determining step in this two-step mechanism. The second mechanism involves a 1,2-siloxyl shift that leads to the direct formation of cyclopropene. The activation barrier of this reaction is calculated to be 40.0 kcal/mol. IRC calculations are performed to trace this 1,2-siloxyl shift in the second mechanism. Since the activation barrier of the direct formation of cyclopropene is energetically comparable to that of the ring-opening reaction toward the cis-silabutadiene, the B3LYP DFT calculations suggest that both reaction pathways are likely to occur under thermal conditions.

    DOI: 10.1021/om0497947

  • Silicon-carbon unsaturated compounds. 69. Reactions of silenes produced thermally from pivaloyl- and adamantoyltris(trimethylsilyl)silane with silyl-substituted butadiynes and enynes Reviewed

    A Naka, H Ohnishi, Miyahara, I, K Hirotsu, Y Shiota, K Yoshizawa, M Ishikawa

    ORGANOMETALLICS   23 ( 18 )   4277 - 4287   2004.8

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    The thermolysis of pivaloyl- and adamantoyltris(trimethylsilyl)silane (1a and 1b) with bis(trimethylsilyl)butadiyne and bis(dimethylphenylsilyl)butadiyne at 120degreesC gave regiospecifically 2-trimethylsiloxy-3-silylethynyl-1-silacyclobut-3-ene derivatives (2a, 2b and 3a, 3b), arising from the reaction of silenes generated thermally from 1a and 1b with the butadiynes. Similar treatment of 1a and 1b in the presence of bis(trimethylsilyl)butadiyne and bis(dimethylphenylsilyl)butadiyne at 160degreesC gave 2,5-dihydro-1,2-oxasilole derivatives (4a, 4b and 5a, 5b). When 2a and 2b were heated in the presence of methanol at 160degreesC, methanol adducts 6a and 6b were obtained, respectively, as the sole product. The ring-opening processes of 2a and the regiochemistry of [2 + 2] cycloaddition of the silene with bis(silyl)butadiyne and bis(silyl)but-1-en-3-yne are discussed on the basis of theoretical treatment. The thermolysis of 1a and 1b with bis(tert-butyldimethylsilyl)butadiyne at 160degreesC produced [2 + 2] cycloadducts (7a and 7b). With bis(tert-butyldimethylsilyl)butadiyne at 220degreesC, 1a and 1b gave 2,5-dihydro-1,2-oxasilole derivatives (8a and 8b). The reaction of 1a and 1b with (E)-1,4-bis(dimethylphenylsilyl)but-1-en-3-yne and (E)-1,4-bis(pentamethyldisilanyl)but-1-en-3-yne at 120degreesC produced regiospecifically 2-trimethylsiloxy-3-[trans-(silyl)ethenyl]-1-silacyclobut-3-ene derivatives (9a, 9b and 10a, 10b). At 200degreesC, similar treatment of 1a and 1b with silyl-substituted but-1-en-3-ynes afforded 2,5-dihydro-1,2-oxasilole derivatives (11a, 11b and 12a, 12b, respectively). UV-vis absorption and fluorescence spectra have been reported.

    DOI: 10.1021/om034213j

  • Mechanistic proposals for direct benzene hydroxylation over Fe-ZSM-5 zeolite Reviewed

    K Yoshizawa, Y Shiota, T Kamachi

    JOURNAL OF PHYSICAL CHEMISTRY B   107 ( 41 )   11404 - 11410   2003.10

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    A mechanism of direct benzene hydroxylation over Fe-ZSM-5 zeolite is discussed from B3LYP density functional theory computations. We demonstrate using a mononuclear iron model supported at the AlO4- site of zeolite that Fe-ZSM-5 zeolite reasonably catalyzes the conversion of benzene to phenol with N2O. A key in this catalytic reaction is that benzene hydroxylation and N2O decomposition occur at the same active site in a well-balanced manner. In the initial stages of the reaction, a reactive oxygen species referred to as "alpha-oxygen" is formed upon decomposition of N2O at the iron active site. The first reaction step is the formation of a complex between benzene and the cc-oxygen species. The C-H activation of benzene leads to an intermediate that involves OH and C6H5 groups as ligands. After forming this intermediate, the reaction has a junction that leads to two possible pathways, depending on the concentration of N2O. The recombination between the OH and C6H5 ligands, which leads to a complex of phenol, can occur when the concentration of N2O is low, whereas the decomposition of nitrous oxide can occur on the intermediate involving OH and C6H5 groups when the N2O concentration is sufficiently high. Calculated potential energy diagrams and reaction kinetics show that the latter pathway is energetically more favorable than the former. We propose that benzene hydroxylation over Fe-ZSM-5 zeolite should proceed in the following way: (1) the formation of the benzene complex at the iron active site, (2) the hydrogen abstraction from benzene, (3) the decomposition of N2O at the active site, (4) the recombination between the OH and C6H5 ligands, and (5) the release of product phenol.

    DOI: 10.1021/jp030240b

  • A theoretical study of the mononuclear non-hem iron complex of phenylalanine hydroxylase (PAH) Reviewed

    Y Shiota, K Yoshizawa

    JOURNAL OF INORGANIC BIOCHEMISTRY   96 ( 1 )   228 - 228   2003.7

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  • A theoretical study of reactivity and regioselectivity in the hydroxylation of adamantane by ferrate(VI) Reviewed

    Y Shiota, N Kihara, T Kamachi, K Yoshizawa

    JOURNAL OF ORGANIC CHEMISTRY   68 ( 10 )   3958 - 3965   2003.5

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    The conversion of adamantane to adamantanols mediated by ferrate (FeO42-), monoprotonated ferrate (HFeO4-), and diprotonated ferrate (H2FeO4) is discussed with the hybrid B3LYP density functional theory (DFT) method. Diprotonated ferrate is the best mediator for the activation of the C-H bonds of adamantane via two reaction pathways, in which 1-adamantanol is formed by the abstraction of a tertiary hydrogen atom (3degrees) and 2-adamantanol by the abstraction of a secondary hydrogen atom (2degrees). Each reaction pathway is initiated by a C-H bond cleavage via an H-atom abstraction that leads to a radical intermediate, followed by a C-O bond formation via an oxygen rebound step to lead to an adamantanol complex. The activation energies for the C-H cleavage step are 6.9 kcal/mol in the I-adamantanol pathway and 8.4 kcal/mol in the 2-adamantanol pathway, respectively, at the B3LY-P/6-311++G** level of theory, whereas those of the second reaction step corresponding to the rebound step are relatively small. Thus, the rate-determining step in the two pathways is the C-H bond dissociation step, which is relevant to the regioselectivity for adamantane hydroxylation. The relative rate constant (3degrees)/(2degrees) for the competing H-atom abstraction reactions is calculated to be 9.30 at 75 degreesC, which is fully consistent with an experimental value of 10.1.

    DOI: 10.1021/jo0207168

  • A spin-orbit coupling study on the spin inversion processes in the direct methane-to-methanol conversion by FeO+ Reviewed

    Y Shiota, K Yoshizawa

    JOURNAL OF CHEMICAL PHYSICS   118 ( 13 )   5872 - 5879   2003.4

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    Possible spin inversion processes in the direct conversion of methane to methanol by the bare FeO+ complex are discussed by means of spin-orbit coupling (SOC) calculations. This reaction proceeds via two transition states (TSs) in the following way; FeO++CH4-->FeO+(CH4)-->[TS1]-->HO-Fe+-CH3-->[TS2]-->Fe+(CH3OH)-->Fe++CH3OH. B3LYP density functional theory calculations show that the potential energies in the quartet and sextet states lie close and involve three crossing seams that can provide a chance of spin-forbidden transition. The spin-forbidden transition leads to a significant decrease in the barrier heights of TS1 and TS2 that correspond to the hydrogen atom abstraction and the methyl shift, respectively. To evaluate the spin-forbidden transition in the reaction pathway, the SOC matrix elements are calculated along the intrinsic reaction coordinate of the reaction. The SOC analysis along the IRC is useful to look at how the FeO+/CH4 reacting system changes its spin multiplicity between the sextet and quartet surfaces. The strength of the SOC between the low-lying quartet state and the sextet state is 133.6 cm(-1) in the reactant complex FeO+(CH4), 21.4 cm(-1) in the hydroxo intermediate HO-Fe+-CH3, and 0.3 cm(-1) in the product complex Fe+(CH3OH). Since the SOC value decreases along the oxidation process, the ease of spin inversion probability is the first crossing seam, the second crossing seam, and the third crossing seam, in this order. (C) 2003 American Institute of Physics.

    DOI: 10.1063/1.1557192

  • Does the hydroperoxo species of cytochrome P450 participate in olefin epoxidation with the main oxidant, compound I? Criticism from density functional theory calculations Reviewed

    T Kamachi, Y Shiota, T Ohta, K Yoshizawa

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN   76 ( 4 )   721 - 732   2003.4

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    Ethylene epoxidation by an iron(III)-hydroperoxo model of cytochroine P450 Fe(OOH)(C20N4H12)(SCH3) is investigated with the B3LYP density functional theory (DFT) method to look at whether or not the iron(III)-hydroperoxo species can participate in olefin epoxidation with the iron(T)-oxo Species (Compound I). The answer is negative. There are two possible entrance channels in the epoxidation reaction, a proximal oxygen transfer mechanism and a distal oxygen transfer mechanism, both mechanisms being stepwise processes involving radical intermediates. In the proximal oxygen transfer mechanism, the homolytic cleavage of the Fe-O bond of the iron(III)-hydroperoxo species initially occurs with a change in the Fe atomic charge from +3 to +2. The proximal oxygen transfer mechanism involves an energetically less stable radical .CH2CH2(OOH). In contrast. in the initial stages of the distal oxygen transfer mechanism, the O-O bond of the hydroperoxo ligand is homolytically cleaned. and the iron(T)-oxo complex thus formed retains a weak interaction with the hydroxy group of the resultant radical intermediate involving .CH2CH2(OH). This mechanism is more realistic, but the activation energy of the transition state of the O-O bond cleavage is comparable to that of the corresponding transition state by hydrogen peroxide. The present result suggests that the mechanism and energetics of ethylene epoxidation remain unchanged by the involvement of the iron-porphyrin complex. The epoxidation of ethylene by a compound I model is also calculated to increase our understanding of olefin epoxidation by P450. The mechanism and energetics of olefin epoxidation by iron(III)-hydroperoxo species are less plausible than epoxidation by compound I.

    DOI: 10.1246/bcsj.76.721

  • Possible photoinduced spin transitions in bis(phenylmethylenyl)[2.2]paracyclophanes. A spin-orbit coupling study Reviewed

    M Kondo, Y Shiota, K Yoshizawa

    JOURNAL OF PHYSICAL CHEMISTRY A   106 ( 34 )   7915 - 7920   2002.8

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    A possible mechanism for the spin transitions in various stacking conformations of bis(phenylmethylenyl)-[2.2]paracyclophanes, which have close-lying lowest singlet, triplet, and quintet spin states, is theoretically investigated by using diphenylcarbene dimers as models. Spin-orbit coupling (SOC) matrix elements, which play an essential role in the spin transition phenomena, are calculated with the effective one-electron spin-orbit Hamiltonian. The SOC between the first excited singlet state and the first excited triplet state and that between the first excited triplet state and the lowest quintet state are strong. The SOC between the first excited quintet state and the first excited triplet state and that between the first excited triplet state and the lowest singlet state are also strong. These results demonstrate that the spin conversion between the low-spin singlet state and the high-spin quintet state can occur via the first excited intermediate-spin triplet state. We propose that possible photoinduced spin-crossover phenomena can be observed in these organic molecular systems.

    DOI: 10.1021/jp020984+

  • Role of molecular distortions in the spin-orbit coupling between the singlet and triplet states of the 4π electron systems C<inf>4</inf>H<inf>4</inf>, C<inf>5</inf>H<inf>5</inf>+, and C<inf>3</inf>H<inf>3</inf>- Reviewed

    Shiota Y, Kondo M, Yoshizawa K

    Journal of Chemical Physics   115 ( 20 )   9243 - 9254   2001.11

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    Role of molecular distortions in the spin-orbit coupling between the singlet and triplet states of the 4 pi electron systems C4H4, C5H5+, and C3H3-
    How molecular distortions enhance the strength of spin-orbit coupling (SOC) between the singlet and triplet states of cyclobutadiene, cyclopentadienyl cation, and cyclopropenyl anion is described. The crossing region of the two potential energy surfaces of cyclobutadiene is characterized by a Jahn-Teller active vibrational mode that can connect the singlet and triplet structures. The spin inversion from triplet to singlet occurs in cyclobutadiene with a structural change from D-4h to D-2h, but the in-plane distortion along the Jahn-Teller mode cannot directly enhance the strength of SOC. Molecular distortions along some C-H out-of-plane bending modes significantly strengthen the SOC in cyclobutadiene. Also in cyclopentadienyl cation, C-H out-of-plane distortions play an essential role in enhancing the strength of SOC. The out-of-plane motions destroy the planarity of cyclobutadiene and cyclopentadienyl cation, leading to rehybridization of their sigma and pi orbitals. This is a main reason that the strength of SOC is enhanced by the C-H out-of-plane bending distortions in these planar molecules. On the other hand, in cyclopropenyl anion the carbon-ring distortion that can connect the triplet and singlet structures is a main factor that dominates the transition between the two states, due to its nonplanarity. (C) 2001 American Institute of Physics.

    DOI: 10.1063/1.1412250

  • A theoretical study of the dynamic behavior of alkane hydroxylation by a compound I model of cytochrome P450 Reviewed

    K Yoshizawa, T Kamachi, Y Shiota

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   123 ( 40 )   9806 - 9816   2001.10

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    Dynamic aspects of alkane hydroxylation mediated by Compound I of cytochrome P450 are discussed from classical trajectory calculations at the B3LYP level of density functional theory. The nuclei of the reacting system are propagated from a transition state to a reactant or product direction according to classical dynamics on a Born-Oppenheimer potential energy surface. Geometric and energetic changes in both low-spin doublet and high-spin quartet states are followed along the ethane to ethanol reaction pathway, which is partitioned into two chemical steps: the first is the H-atom abstraction from ethane by the iron-oxo species of Compound I and the second is the rebound step in which the resultant iron-hydroxo complex and the ethyl radical intermediate react to form the ethanol complex. Molecular vibrations of the C-H bond being dissociated and the O-H bond being formed are significantly activated before and after the transition state, respectively, in the H-atom abstraction. The principal reaction coordinate that can represent the first chemical step is the C-H distance or the O-H distance while other geometric parameters remain almost unchanged. The rebound process begins with the iron-hydroxo complex and the ethyl radical intermediate and ends with the formation of the ethanol complex, the essential process in this reaction being the formation of the C-O bond. The H-O-Fe-C dihedral angle corresponds to the principal reaction coordinate for the rebound step, When sufficient kinetic energy is supplied to this rotational mode, the rebound process should efficiently take place. Trajectory calculations suggest that about 200 fs is required for the rebound process under specific initial conditions, in which a small amount of kinetic energy (0.1 kcal/mol) is supplied to the transition state exactly along the reaction coordinate. An important issue about which normal mode of vibration is activated during the hydroxylation reaction is investigated in detail from trajectory calculations. A large part of the kinetic energy is distributed to the C-H and O-H stretching modes before and after the transition state for the H-atom abstraction, respectively, and a small part of the kinetic energy is distributed to the Fe-O and Fe-S stretching modes and some characteristic modes of the porphyrin ring. The porphyrin marker modes Of nu (3) and nu (4) that explicitly involve Fe-N stretching motion are effectively enhanced in the hydroxylation reaction. These vibrational modes of the porphyrin ring can play an important role in the energy transfer during the enzymatic process.

    DOI: 10.1021/ja010593t

  • A theoretical study of the dynamical aspects of alkane hydroxylation by compound I of cytochrome p450 Reviewed

    K Yoshizawa, T Kamachi, Y Shiota

    JOURNAL OF INORGANIC BIOCHEMISTRY   86 ( 1 )   488 - 488   2001.8

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  • A theoretical study of alcohol oxidation by ferrate Reviewed

    T Ohta, T Kamachi, Y Shiota, K Yoshizawa

    JOURNAL OF ORGANIC CHEMISTRY   66 ( 12 )   4122 - 4131   2001.6

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    The conversion of methanol to formaldehyde mediated by ferrate (FeO42-), monoprotonated ferrate (HFeO4-), and diprotonated ferrate (H2FeO4) is discussed with the hybrid B3LYP density functional theory (DFT) method. Diprotonated ferrate is the best mediator for the activation of the O-H and C-H bonds of methanol via two entrance reaction channels: (1) an addition-elimination mechanism that involves coordination of methanol to diprotonated ferrate; (2) a direct abstraction mechanism that involves H atom abstraction from the O-H or C-H bond of methanol. Within the framework of the polarizable continuum model (PCM), the energetic profiles of these reaction mechanisms in aqueous solution are calculated and investigated. In the addition-elimination mechanism, the O-H and C-H bonds of ligating methanol are cleaved by an oxo or hydroxo ligand, and therefore the way to the formation of formaldehyde is branched into four reaction pathways. The most favorable reaction pathway in the addition-elimination mechanism is initiated by an O-H cleavage via a four-centered transition state that leads to intermediate containing an Fe-O bond, followed by a C-H cleavage via a five-centered transition state to lead to formaldehyde complex. In the direct abstraction mechanism, the oxidation reaction can be initiated by a direct H atom abstraction from either the O-H or C-H bond, and it is branched into three pathways for the formation of formaldehyde. The most favorable reaction pathway in the direct abstraction mechanism is initiated by C-H activation that leads to organometallic intermediate containing an Fe-C bond, followed by a concerted H atom transfer from the OH group of methanol to an oxo ligand of ferrate. The first steps in both mechanisms are all competitive in energy, but due to the significant energetical stability of the organometallic intermediate, the most likely initial reaction in methanol oxidation by ferrate is the direct C-H bond cleavage.

    DOI: 10.1021/jo001193b

  • Reaction Pathways for the He, Li, and Li+ Penetrations of the Benzene Ring Reviewed International journal

    Takashi Yumura, Yoshihito Shiota, Kazunari Yoshizawa

    JCPE Journal   13 ( 3 )   169 - 176   2001.1

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    DOI: 10.14827/jccj1999.13.169

  • Energetics for the oxygen rebound mechanism of alkane hydroxylation by the iron-ore species of cytochrome p450 Reviewed

    K Yoshizawa, Y Shiota, Y Kagawa

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN   73 ( 12 )   2669 - 2673   2000.12

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    Density-functional-theory calculational results on the reaction pathway for alkane hydroxylation by a compound I model of cytochrome P450 are discussed. Our calculations demonstrate that the transition state for the H-atom abstraction of ethane involves a linear (Fe)O . . .H . . .C array and that the resultant carbon radical is bound to the iron-hydroxo species. This comptational result is partly consistent with the oxygen rebound mechanism in that the direct H-atom abstraction by the iron-ore species takes place in the initial stages of the reaction pathway. However, the iron-hydroxo species cannot be viewed as a stable reaction intermediate in view of the energy diagram. Our results may not be consistent with the model of a free radical species with a finite lifetime and barrier to displacement of the OH group from the iron center that is commonly assumed and typically stated for the oxygen rebound mechanism.

    DOI: 10.1246/bcsj.73.2669

  • Methane-to-methanol conversion by first-row transition-metal oxide ions: ScO+TiO+, VO+, CrO+, MnO+, FeO+, CoO+, NiO+, and CuO+ Reviewed

    Y Shiota, K Yoshizawa

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   122 ( 49 )   12317 - 12326   2000.12

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    The reaction pathway and energetics for methane-to-methanol conversion by first-row transition-metal oxide ions (MO(+)s) are discussed from density functional theory (DFT) B3LYP calculations, where M is Sc. Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. The methane-to-methanol conversion by these MO+ complexes is proposed to proceed in a two-step manner via two transition states: MO+ + CH4 --> OM+(CH4) --> [TS] --> OH-M+-CH3 --> [TS] --> M+(CH3OH) --> M+ + CH3OH. Both high-spin;and low-spin potential energy surfaces are characterized in detail. A crossing between the high-spin and the low-spin potential energy surfaces occurs once near the exit channel for ScO+, TiO+, VO+ CrO+, and MnO+, but it occurs twice in the entrance and exit channels for FeO+, CoO+, and NiO+. Our calculations strongly suggest that spin Inversion can occur near a crossing region of potential energy surfaces and that it can play a significant role in decreasing the barrier heights of these transition states. The reaction pathway from methane to methanol is uphill in energy on the early MO+ complexes (ScO+, TiO+, and VO+); thus, these complexes are not good mediators for the formation of methanol. On the other hand, the late MO+ complexes (FeO+, NiO+, and CuO+) are expected from the general energy profiles of the reaction pathways to efficiently convert methane to methanol, Measured reaction efficiencies and methanol branching ratios for MnO+, FeO+, CoO+, and NiO+ are rationalized from the energetics of the high-spin and the low-spin potential energy surfaces. The energy diagram for the methane-to-methanol conversion by CuO+ is downhill toward the product direction, and thus CuO+ is likely to be an excellent mediator for methane hydroxylation.

    DOI: 10.1021/ja0017965

  • Kinetic isotope effects in a C-H bond dissociation by the iron-oxo species of cytochrome P450 Reviewed

    K Yoshizawa, Y Kagawa, Y Shiota

    JOURNAL OF PHYSICAL CHEMISTRY B   104 ( 51 )   12365 - 12370   2000.12

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    Kinetic isotope effects (KIEs) in the electronic process of the H-atom abstraction from substrate ethane by a compound I model of cytochrome P450 are discussed at the B3LYP level of density functional theory. Our calculations demonstrate that the transition State for the H-atom abstraction involves a linear (Fe)O . .H . . .C array and that, a resultant radical species with a spin density of nearly one is bound to an iron-hydroxo complex, followed by recombination and release of product ethanol. Although the reacting system involves this carbon radical species in the course of the hydroxylation, in view of the energy profile of the reaction pathway it cannot be viewed as a stable reaction intermediate with a finite lifetime. The KIEs calculated with transition state theory are significantly dependent on temperature and substituents, falling in a range of 7-13 at 300 K.

    DOI: 10.1021/jp001950+

  • Conversion of methane to methanol on diiron and dicopper enzyme models of methane monooxygenase: A theoretical study on a concerted reaction pathway Reviewed

    K Yoshizawa, A Suzuki, Y Shiota, T Yamabe

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN   73 ( 4 )   815 - 827   2000.4

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    We present theoretical analyses for the conversion of methane to methanol on a diiron model of soluble methane monooxygenase (sMMO) and on dicopper models of particulate methane monooxygenase (pMMO) using the hybrid density-functional-theory B3LYP method. Methane is proposed to be reasonably converted into methanol in a two-step concerted manner on the dinuclear enzyme models. The first step in our proposal is concerted H atom abstraction of methane via a four-centered transition state (TS1) and the second step is concerted methyl migration via a three-centered transition state (TS2). The general features of the electronic process are identical to those of the gas-phase process for the methane-methanol conversion by the bare FeO+ complex. The concerted H atom abstraction and the direct H atom abstraction via a transition state with a linear C-H-O(Fe) array are compared using the dinuclear models. The transition state for the direct H atom abstraction (TSd) on the diiron model is found in the spin undecet state; however, that on the dicopper models is found in the doubler stare. Kinetic isotope effects (k(H)/k(D)) are calculated and analyzed for the concerted and the direct H atom abstraction mechanisms using the transition state theory. Calculated k(H)/k(D) values for the concerted process and the direct process are 9 and 14, respectively, at 300 K.

    DOI: 10.1246/bcsj.73.815

  • Femtosecond dynamics of the methane-methanol and benzene-phenol conversions by an iron-oxo species Reviewed

    K Yoshizawa, Y Shiota, Y Kagawa, T Yamabe

    JOURNAL OF PHYSICAL CHEMISTRY A   104 ( 12 )   2552 - 2561   2000.3

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    Femtosecond dynamic behavior of the methane-methanol conversion by the bare iron-ore complex (FeO+) is presented using the B3LYP density-functional-theory (DFT) method. We propose that the reaction pathway for the direct methane-methanol conversion is partitioned into the H atom abstraction via a four-centered transition state and the methyl migration via a three-centered transition state. It is demonstrated that both the H atom abstraction and the methyl migration occur in a concerted manner in a time scale of 100 fs. The concerted H atom abstraction and the direct H atom abstraction via a transition state with a linear C-H-O(Fe) array are compared. The direct H atom abstraction of methane is predicted to occur in a time scale of 50 fs. Isotope effects on the concerted and the direct H(D) atom abstractions are also computed and analyzed in the FeO+/methane system. Predicted values of the kinetic isotope effect (k(H)/k(D)) for the H(D) atom abstraction of methane are 9 in the concerted mechanism and 16 in the direct abstraction mechanism at 300 K. Dynamics calculations are also carried out on the benzene-phenol conversion by the FeO+ complex. The general profile of the electronic process of the benzene-phenol conversion is identical to that of the methane-methanol conversion with respect to essential bonding characters. It is demonstrated that the concerted H atom abstraction and the phenyl migration require 200 and 100 fs to be completed, respectively, in the FeO+/benzene system.

    DOI: 10.1021/jp992464t

  • Direct methane-methanol and benzene-phenol conversions on Fe-ZSM-5 zeolite: Theoretical predictions on the reaction pathways and energetics Reviewed

    K Yoshizawa, Y Shiota, T Yumura, T Yamabe

    JOURNAL OF PHYSICAL CHEMISTRY B   104 ( 4 )   734 - 740   2000.2

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    The reaction pathways and the energetics for the direct methane-methanol and benzene-phenol conversions that occur on the surface of Fe-ZSM-5 zeolite are analyzed from B3LYP DFT computations. We propose a reasonable model for "alpha-oxygen", a surface oxygen species responsible For the catalytic reactivities of Fe-ZSM-5 zeolite. Our model involves an iron-ore species on the AlO4 surface site of the zeolite as a catalytic active center and as a source of oxygen. The essential features of the reaction pathways for the methane-methanol and benzene-phenol conversions are identical, especially in bonding characters, In the initial stages of each reaction, methane or benzene comes into contact with the active iron site of the "alpha-oxygen" model, leading to the reactant (methane or benzene) complex. After the initial complex is formed, each reaction takes place in a two-step concerted manner, via neither radical species nor ionic intermediates. The concerted reaction pathway for the methane (benzene) hydroxylation involves an H atom abstraction and a methyl (phenyl) migration at the iron active center. From computed energetics for the reaction pathways, we predict that the benzene hydroxylation should be energetically more favorable than the methane hydroxylation.

    DOI: 10.1021/jp991844b

  • Formation of an iron-oxo species upon decomposition of dinitrogen oxide on a model of Fe-ZSM-5 zeolite Reviewed

    K Yoshizawa, T Yumura, Y Shiota, T Yamabe

    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN   73 ( 1 )   29 - 36   2000.1

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    The so-called "alpha-oxygen" on Fe-ZSM-5 zeolite, a surface oxygen species responsible for high reactivity in oxidation of methane and of benzene, has been investigated. We present from density-functional-theory (DFT) calculations how such a reactive surface species is generated upon decomposition of dinitrogen oxide (N2O) and propose a possible form of "alpha-oxygen" on Fe-ZSM-5 zeolite. In the initial stages of the reactions, a complex involving an Fe(ON2) moiety is formed, followed by dissociation into an iron-ore species and N-2. The activation energy for the decomposition of N2O on a possible iron active site model of Fe-ZSM-5 zeolite is predicted to be 2.4 kcal mol(-1) at the B3LYP level of theory. Therefore the decomposition of N2O is expected to take place easily at a coordinatively unsaturated iron active center supported on zeolite. The iron-ore species thus formed should play an essential role in the direct hydroxylation of methane, benzene, and other hydrocarbons if it involves a coordinatively unsaturated iron. The oxygen exchange on the iron-ore complex was also investigated. The activation energy for the oxygen exchange on the "alpha-oxygen" is predicted to be 26.8 kcal mol(-1). We propose that the bare FeO+ complex and the so-called "alpha-oxygen" on Fe-ZSM-5 zeolite involve similar catalytic active centers responsible for similar catalytic functions for methane and benzene.

    DOI: 10.1246/bcsj.73.29

  • Intrinsic reaction coordinate analysis of the conversion of methane to methanol by an iron-oxo species: A study of crossing seams of potential energy surfaces Reviewed

    K Yoshizawa, Y Shiota, T Yamabe

    JOURNAL OF CHEMICAL PHYSICS   111 ( 2 )   538 - 545   1999.7

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    Crossing seams between the potential energy surfaces and possible spin inversion processes for the direct conversion of methane to methanol by the bare FeO+ species are discussed by means of the intrinsic reaction coordinate (IRC) approach. There are three crossing seams between the sextet and the quartet potential energy surfaces, and spin inversion should occur twice in the entrance and the exit channels; FeO+((6)Sigma(+)) + CH4((1)A(1)) --> OFe+(CH4)((6)A) --> TS1((4)A') --> HO-Fe+-CH3((4)A) --> TS2 ((4)A) --> Fe+(CH3OH)((4)A) --> Fe+(D-6) + CH3OH((1)A'). The first crossing seam exists in prior to TS1, a four-centered transition state for the cleavage of a C-H bond of methane. This crossing seam is the most important aspect in this reaction pathway because the molecular system should change its spin multiplicity from the sextet state to the quartet state near this crossing region, leading to a significant decrease in the barrier height of TS1 from 31.1 to 22.1 kcal/mol at the B3LYP level of density functional theory. The second crossing seam occurs in the vicinity of the hydroxy intermediate (HO-Fe+-Ch(3)), but this crossing seam would not play a significant role because the quartet IRC valley always lies below the sextet one in this region of reaction coordinate and accordingly the molecular system would preferentially move on the quartet potential energy surface. The third crossing seam exists in the exit channel in which the elimination of methanol occurs from the product complex. This crossing seam will again lead to spin inversion from the quartet to the sextet state, by which the elimination energy can be decreased from 57.2 to 37.4 kcal/mol in the FeO+/CH4 system. (C) 1999 American Institute of Physics. [S0021-9606(99)01926-1].

    DOI: 10.1063/1.479333

  • Reaction pathway for the direct benzene hydroxylation by iron-ore species Reviewed

    K Yoshizawa, Y Shiota, T Yamabe

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   121 ( 1 )   147 - 153   1999.1

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    The direct benzene hydroxylation by an iron-ore species is discussed from density-functional-theory (DFT) calculations. The proposed reaction pathway is FeO+ + C6H6 --> OFe+(C6H6) --> [TS1] --> HO-Fe+-C6H5 --> [TS2] --> Fe+(C6H5OH) --> Fe+ + C6H5OH, in which TS means transition state. This reaction is initiated by the formation of the reactant complex, OFe+(C6H6), exhibiting an eta(2)-C6H6 binding mode; benzene C-H bonds are activated on this complex due to significant electron transfer from the benzene to the iron-oxo species. The reaction should proceed in a concerted manner, neither via the formation of radical species nor ionic intermediates. The reaction mechanism is quite similar to the two-step concerted mechanism that we have proposed originally for the direct methane hydroxylation by an iron-ore species. The quartet potential energy surface affords a low-cost reaction pathway for the benzene hydroxylation, spin inversion being unimportant in contrast to the methane hydroxylation in which crossing between the sextet and quartet potential energy surfaces plays an important role. We suggest that our two-step concerted mechanism should be widely applicable to hydrocarbon hydroxylations catalyzed by transition-metal oxides if coordinatively unsaturated metal oxides are responsible for such important catalytic reactions.

    DOI: 10.1021/ja981525i

  • Abstraction of the hydrogen atom of methane by iron-oxo species: The concerted reaction path is energetically more favorable Reviewed

    K Yoshizawa, Y Shiota, T Yamabe

    ORGANOMETALLICS   17 ( 13 )   2825 - 2831   1998.6

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    Two kinds of H-atom abstractions from methane by iron-ore complexes with different charges are discussed from density functional theory calculations. A concerted H-atom abstraction via a four-centered transition state is shown to be energetically more favorable than a direct H-atom abstraction via a transition state with a linear C-H-O array. Iron-(IV)-oxo complexes appear to be the most effective for the cleavage of the C-H bond of alkanes in the concerted mechanism, which is rationalized from qualitative orbital interaction analyses. The results of this paper support the establishment of the two-step concerted mechanism that we have proposed for alkane hydroxylations by iron-ore species. The proposed reaction mechanism may have relevance to our understanding of some catalytic and enzymatic processes concerning alkane hydroxylations if coordinatively unsaturated transition-metal oxides are responsible for such important chemical reactions.

    DOI: 10.1021/om980067j

  • Methane-methanol conversion by MnO+, FeO+, and CoO+: A theoretical study of catalytic selectivity Reviewed

    K Yoshizawa, Y Shiota, T Yamabe

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   120 ( 3 )   564 - 572   1998.1

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    The entire reaction pathway for the gas-phase methane-methanol conversion by late transition-metal-oxide ions, MnO+, FeO+, and CoO+, is studied using an ab initio hybrid (Hartree-Fock/density-functional) method. For these oxo complexes, the methane-methanol conversion is proposed to proceed via two transition states (TSs) in such a way MO+ + CH4 --> OM+(CH4) --> [TS1] --> HO-M+-CH3 --> [TS3] --> M+(CH3OH) --> M+ + CH3OH, where M is Mn, Fe, and Co. A crossing between high-spin and low-spin potential energy surfaces occurs both at the entrance channel and at the exit channel for FeO+ and CoO+, but it occurs only once near TS2 for MnO+. The activation energy from OMn+(CH4) to HO-Mn+-CH3 via TS1 is calculated to be 9.4 kcal/mol, being much smaller than 22.1 and 30.9 kcal/mol for FeO+ and CoO+, respectively. This agrees with the experimentally reported efficiencies for the reactions. The excellent agreement between theory and experiment indicates that HO-M+-CH3 plays a central role as an intermediate in the reaction between MO+ and methane and that the reaction efficiency is most likely to be determined by the activation energy from OM+(CH4) to HO-M+-CH3 via TS1. We discuss in terms of qualitative orbital interactions why MnO+ (d(4) oxo complex) is most effective for methane C-H bond activation. The activation energy from HO-M+-CH3 to M+(CH3OH) via TS2 is computed to be 24.6, 28.6, and 35.9 kcal/mol for CoO+, FeO+, and MnO+, respectively. This result explains an experimental result that the methanol-branching ratio in the reaction between MO+ and methane is 100% in CoO+, 41% in FeO+, and < 1% in MnO+. We demonstrate that both the barrier heights of TS1 and TS2 would determine general catalytic selectivity for the methane-methanol conversion by the MO+ complexes.

    DOI: 10.1021/ja971723u

  • Possible nitrogen fixation disilabutadiene Reviewed

    K Yoshizawa, Y Shiota, S Kang, T Yamabe

    ORGANOMETALLICS   16 ( 23 )   5058 - 5063   1997.11

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    A possible nitrogen fixation based on a Diels-Alder reaction of 1,4-disila-1,3-butadiene and N-2 is discussed. The activation energy from the reactants to the product, a six-membered ring of C2Si2N2, was computed to be only 5.1 kcal/mol at the B3LYP/6-311G** level of density functional theory. QCISD(T)/6-31G**//CASSCF/6-31G** calculations also gave 8.0 kcal/mol comparable to the B3LYP value. These computed activation energies are smaller than that of the well-known Diels-Alder reaction of butadiene and ethylene, 24.8 kcal/mol at the B3LYP/6-31G* level (Goldstein, E.; Beno, B.; Houk, K. N. J. Am. Chem. Soc. 1996, 118, 6036), and consequently, this unique reaction would proceed under mild conditions if this reactive species, disilabutadiene, is prepared. The triple bond of N-2 is partially cleaved in a reductive manner to lead to the formation of an N=N double bond. Orbital interaction analyses suggest that one of the degenerate pi* LUMOs of N-2 has a good interaction with the high-lying HOMO of disilabutadiene, and this interaction should contribute to significant electron transfer from disilabutadiene to N-2. 1,4-Disila-1,3-butadiene, could be prepared by thermal ring opening of 1,2-disilacyclobutene; the activation barrier for a symmetry-allowed conrotatory process of the two silylene groups was calculated to be 40.9 kcal/mol at the B3LYP/6-311G** level and 47.6 kcal/mol at the QCISD(T)/6-31G**//CASSCF/6-31G** level. We, thus, expect the artificial nitrogen fixation to occur when 1,2-disilacyclobutene and N-2 gas are heat-treated in a sealed tube.

    DOI: 10.1021/om970553r

  • Reaction paths for the conversion of methane to methanol catalyzed by FeO+ Reviewed

    K Yoshizawa, Y Shiota, T Yamabe

    CHEMISTRY-A EUROPEAN JOURNAL   3 ( 7 )   1160 - 1169   1997.7

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    We propose possible theoretical reaction paths for the conversion of methane to methanol catalyzed by FeO+. The geometric and electronic structures for the reactant. product. intermediates. and transition states were calculated and analyzed in detail by means of a hybrid Hartree-Fock/density functional method. Sestet and quartet spin states were taken into consideration in the analysis of the reaction paths. The conversion of methane to methanol was shown to proceed through basic concerted hydrogen- and methyl-shift reactions. A fragment molecular orbital analysis for the Formation of the reactant complex, OFe+-CH4. which plays an important role in the initial stage of methane activation. was carried out in order to understand the nature of the interesting Fe-C bond. The five-coordinate methane in the reactant complex was calculated to have a C-3v-type geometry. Each reaction path presented in this gaper includes an important insertion species. HO-Fe+-CH3 or H-Fe+-OCH3, and two transition states. Thus. there are several kinds of reaction paths. if the high-spin sextet and low-spin quartet states are taken into consideration. A reaction towards the hydroxy intermediate, HO - Fe+ - CH3, was found to be more favorable in both the sextet and quartet spin states from the viewpoint of activation energy, and this intermediate is extremely stable. It was found from intrinsic reaction coordinate (IRC) analyses that two basic reactions coexist, namely hydrogen or methyl migration between the reactant and the methoxy intermediate, H-Fe+-OCH3. This transition state is interesting, because the two transition states resulting from C-H bond cleavage and methyl migration are located in the same region of space on the potential energy surfaces. IRCs are partially shown for the complicated first halves of the total reaction paths.

    DOI: 10.1002/chem.19970030722

  • Orbital interaction and vibrational mode analyses for phase transitions of BaTiO3

    T Takeuchi, K Yoshizawa, Y Shiota, O Nakamura, H Kageyama, T Yamabe

    JOURNAL OF MATERIALS CHEMISTRY   7 ( 6 )   969 - 975   1997.6

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    The phase transitions of ATiO(3)-type perovskite structures, mainly those of barium titanate (BaTiO3), aro studied theoretically in terms of orbital interactions and vibrational modes. Vibrational analyses for fundamental TiO6 clusters, up to Ti8O36, are performed with a hybrid (Hartree-Fock/density functional) method. Important structural distortions from the high symmetry cubic phase are rationalized by a second-order perturbational treatment of quantum chemistry. The orbital symmetry argument based on group theory indicates that the transition density around frontier molecular orbitals plays an important role in the motions of ions at the transition temperatures. Our orbital interaction and vibrational mode analyses of the phase transitions are consistent with the soft mode theory of Cochran.

    DOI: 10.1039/a607475h

  • Density functional study on possible peroxo form of non-heme diiron enzyme model Invited Reviewed International journal

    Kazunari Yoshizawa, Yasunori Yokomichi, Yoshihito Shiota, Takehiro Ohta, Tokio Yamabe

    Chemistry Letters   ( 7 )   587 - 588   1997.1

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    Dioxygen binding to the active dinuclear iron site of methane monooxygenase (MMO) is theoretically analyzed with a density functional method. The μ-η1:η1-O2 mode was calculated to be the most favorable binding mode of dioxygen to a supposed active site of MMO that contains two five-coordinate irons(II).

  • Novel aspects of the [1,3] sigmatropic silyl shift in allylsilane Reviewed

    T Yamabe, K Nakamura, Y Shiota, K Yoshizawa, S Kawauchi, M Ishikawa

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   119 ( 4 )   807 - 815   1997.1

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    Ab initio molecular orbital calculations of the C-CCSi torsion and the [1,3] sigmatropic silyl shift in allylsilane (SiC3H8, 1) have been carried out. It is clarified that the skew conformer of 1 is more stable than other conformers. Its torsional energy depends on the sigma-pi hyperconjugation as compared with that of 1-butene (2). In the [1,3] silyl shift, the reaction coordinate of the silyl-group migration in the early and final stages is congruent with that of the C=CCSi torsion near the skew conformer. Divergence points on the inversion and retention paths are discussed from the viewpoint of the degree of nonplanarity of the migrating silyl group. The activation energy along the retention path is calculated to be lower than that along the inversion path at various levels of theory, which is in remarkable contrast to 2, in which the inversion path is more favorable. From the energetical viewpoint, the [1,3] shift of the silyl group is expected to proceed with retention of the silicon configuration at the migrating center. Although this looks like an exception to the Woodward-Hoffmann rules, this may be caused by the nearly degenerate HOMO and (HOMO-1) in the transition state on the inversion path in 1.

    DOI: 10.1021/ja9623525

  • Cleavage of C-H bond of methane on intermediate Q of methane monooxygenase Reviewed International journal

    Kazunari Yoshizawa, Takehiro Ohta, Yoshihito Shiota, Tokio Yamabe

    Chemistry Letters   ( 12 )   1213 - 1214   1997.1

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    A possible reaction pathway for the C-H bond cleavage of methane on intermediate Q of methane monooxygenase is studied theoretically. We propose that the activation of methane C-H bond by Q, suggested to involve a high valent Fe2(μ-O)2 diamond core, should occur through the formation of the Q(CH4) complex with an Fe-C bond and Fe-H bonds, followed by a concerted H atom abstraction via a four-centered transition state.

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Books

  • 高機能性金属錯体が拓く触媒科学 15章 計算化学が先導する酵素触媒反応の設計

    堀 優太・塩田 淑仁・吉澤 一成(Role:Joint author)

    化学同人  2021.6 

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    Language:Japanese   Book type:Scholarly book

    新規反応開発では金属錯体触媒の創製が鍵を握っており,現在まで多種多様な金属錯体が合成反応に利用されてきた.現在,工業的に利用されている汎用錯体触媒は,そもそも独創的な配位子設計によるものが多く,それが発展して実用化に至っている.本書では,省エネルギー,資源の有効利用などの要求に応えうる,次世代の物質合成を支える分子変換の実現に向けて,独創的な触媒反応を開発している第一線の研究を解説する.

  • Direct Hydroxylation of Methane Theoretical Study of the Direct Conversion of Methane by First-Row Transition-Metal Oxide Cations in the Gas Phase

    Yoshihito Shiota, Kazunari Yoshizawa(Role:Joint author)

    springer  2020.12 

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    This book focuses on theoretical and computational studies by the editor’s group on the direct hydroxylation of methane, which is one of the most challenging subjects in catalyst chemistry. These studies of more than 20 years include gas-phase reactions by transition-metal oxide ions, enzymatic reactions by two types of methane monooxygenase (soluble and particulate MMO), catalytic reactions by metal-exchanged zeolites, and methane C–H activation by metal oxide surfaces. Catalyst chemistry has been mostly empirical and based on enormous experimental efforts. The subject of the title has been tackled using the orbital interaction and computations based on extended Hückel, DFT, and band structure calculations. The strength of the theoretical studies is in the synergy between theory and experiment. Therefore, the group has close contacts with experimentalists in physical chemistry, catalyst chemistry, bioinorganic chemistry, inorganic chemistry, and surface chemistry. This resulting book will be useful for the theoretical analysis and design of catalysts.

  • 金属錯体の量子・計算化学 (錯体化学会選書)

    大阪大学教授 山口 兆・京都大学名誉教授 榊 茂好 名古屋工業大学名誉教授 増田秀樹 編著 磯部 寛・江原正博・奥村光隆・蒲池高志・川上貴資・岸 亮平・北河康隆 倉重佑輝・古賀伸明・小関史朗・佐藤啓文・塩田淑仁・重田育照・庄司光男 杉本 学・鷹野 優・高柳昌芳・田中晃二・常田貴夫・中井浩巳・長岡正隆 中嶋隆人・中谷直輝・中野晴之・中野雅由・波田雅彦・土方 優・福住俊一 福田良一・柳井 毅・山中秀介・横川大輔・吉澤一成 共著(Role:Joint author)

    三共出版  2014.10 

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    錯体の構造・機能・反応等を理論的に解釈し,基礎研究から注目されている生物・材料まで錯体を合理的にデザインする。

Presentations

  • 量子化学計算を利用した反応機構解析

    塩田 淑仁

    フレッシュマンゼミナール  2021.5 

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    Event date: 2021.5

    Language:Japanese   Presentation type:Oral presentation (invited, special)  

    Venue:オンライン   Country:Japan  

  • 計算化学による1Ru置換型Keggin-typeポリ酸による水中での選択的ベンゼン水酸化反応の提案

    #池田 京 塩田 淑仁、吉澤 一成

    日本化学会  2021.3 

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    Event date: 2021.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  • 計算化学によるメタン水酸化反応を触媒する新規イリジウム錯体の提案

    #池田 京 Muhammad Haris Mahyuddin、  塩田 淑仁、吉澤 一成

    第53回酸化反応討論会  2020.11 

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    Event date: 2020.11

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  • Ni-ZSM-5によるメタノール酸化反応の理論的研究

    #田中 靖也 Muhammad Haris Mahyuddin、  塩田 淑仁、吉澤 一成

    日本コンピュータ化学会2020年秋季年会  2020.11 

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    Event date: 2020.11

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  • 計算化学による新規メタン水酸化錯体の提案

    #池田 京 Muhammad Haris Mahyuddin、  塩田 淑仁、吉澤 一成

    日本コンピュータ化学会2020年秋季年会  2020.11 

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    Event date: 2020.11

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  • Cu-ZSM-5によるメタノール過剰酸化反応の理論的研究

    #北川 遼太朗 Muhammad Haris Mahyuddin、  塩田 淑仁、吉澤 一成

    第126回触媒討論会  2020.9 

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    Event date: 2020.9 - 2020.11

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  • Zn-ZSM-5によるメタン変換反応の理論的研究

    #田中 靖也 Muhammad Haris Mahyuddin、  塩田 淑仁、吉澤 一成

    第126回触媒討論会  2020.9 

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    Event date: 2020.9 - 2020.11

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  • B12-TiO2複合触媒による還元的脱塩素化反応の理論研究

    塩田 淑仁 #今村 健仁、嶌越 恒、吉澤 一成

    日本化学会  2021.3 

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    Event date: 2020.3 - 2021.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  • Theoretical Studies on the Role of Amino-Acid Residue on the O–O Bond Cleavage of Cu2O2 Adduct in pMMO International conference

    阿部 司 宮西真由子、堀 優太、塩田淑仁、吉澤一成

    ISABC15  2019.6 

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    Event date: 2019.6

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:奈良   Country:Japan  

  • 単核銅(II)スーパーオキソ錯体によるカルボニル化合物の触媒的炭素-炭素結合形成反応

    阿部司 堀優太 塩田淑仁 太田雄大 森本祐麻 杉本秀樹 小倉尚志 吉澤一成 伊東忍

    第121回触媒討論会  2018.9 

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    Event date: 2018.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:東京   Country:Japan  

  • 触媒反応は計算化学でどこまで明らかにできるのか?

    塩田 淑仁

    触媒学会  2017.9 

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    Event date: 2017.9

    Language:Japanese   Presentation type:Oral presentation (invited, special)  

    Venue:オンライン   Country:Japan  

  • ルテニウムオキソ錯体を活性種とするメタノールの酸化反応に関する理論的研究

    髙橋翔也 塩田 淑仁 小島隆彦 吉澤 一成

    分子科学討論会  2013.9 

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    Event date: 2013.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:京都   Country:Japan  

  • スピンクロスオーバー錯体におけるポテンシャルエネルギー面交差に関する理論的研究

    塩田 淑仁 阿部誉史 吉澤 一成

    分子科学討論会  2013.9 

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    Event date: 2013.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:京都   Country:Japan  

  • 含ガリウムゼオライトによるフランの熱分解反応に関する理論的研究

    鈴木達也 塩田 淑仁 吉澤 一成

    分子科学討論会  2013.9 

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    Event date: 2013.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:京都   Country:Japan  

  • 銅二核オキソ種によるメタン活性化の理論的研究

    塩田 淑仁・吉澤 一成

    春季年会  2013.3 

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    Event date: 2013.3 - 2012.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:滋賀   Country:Japan  

  • Ga-ZSM-5によるフランの分解反応に関する理論的研究

    鈴木 達也・高橋 翔也・塩田 淑仁・吉澤 一成

    春季年会  2013.3 

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    Event date: 2013.3 - 2012.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:滋賀   Country:Japan  

  • ルテニウム(IV)-オキソ錯体によるメタノールの酸化反応に関する理論的研究

    高橋 翔也・阿部 誉史・塩田 淑仁・小島 隆彦・吉澤 一成

    春季年会  2013.3 

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    Event date: 2013.3 - 2012.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:滋賀   Country:Japan  

  • Co 錯体の原子価互変異性に関する理論的研究

    塩田 淑仁

    錯体討論会  2012.9 

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    Event date: 2012.11

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:富山   Country:Japan  

  • 銅二核活性点におけるメタン活性化の理論的研究

    塩田 淑仁、ゲルゲイ ユハース、吉澤 一成

    触媒討論会  2012.9 

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    Event date: 2012.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:福岡   Country:Japan  

  • 銅二核活性点におけるメタン酸化反応に関する理論的研究

    塩田 淑仁、ゲルゲイ ユハース、吉澤 一成

    春季年会  2012.3 

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    Event date: 2012.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:滋賀   Country:Japan  

  • 金属錯体のスピン交差に関する理論的研究 Invited

    塩田淑仁

    統合物質国内シンポ  2011.11 

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    Event date: 2011.11

    Presentation type:Oral presentation (general)  

    Venue:名古屋   Country:Japan  

  • 銅二核活性点におけるメタン酸化反応に関する理論的研 International conference

    塩田淑仁 ゲルゲイ・ユハース 吉澤一成

    酸化反応討論会  2011.11 

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    Event date: 2011.11

    Presentation type:Oral presentation (general)  

    Venue:大阪   Country:Japan  

  • 銅二核錯体上での酸素活性化に関するチロシン残基の役割に関する理論的研究

    塩田淑仁 ゲルゲイ・ユハース 吉澤一成

    触媒討論会  2011.9 

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    Event date: 2011.9

    Presentation type:Oral presentation (general)  

    Venue:北見   Country:Japan  

    メタンモノオキシゲナーゼ(pMMO)はX線構造解析や最近の実験的研究から二核銅及び単核銅の活性点を持つことが明らかとなったものの、その活性化の仕組みや反応機構は分子レベルでは未だによく分かっていない。我々は活性中心の二核銅酸素錯体の電子状態が+1価と+2価の混合原子価のときにメタンと効率よく反応することをDFT計算から明らかした。今回、我々はチロシン残基からの水素原子の付加により、bis(μ-Oxo)Cu(III)Cu(III)からメタンと反応可能な活性種を生じる可能性について理論的に検討した

  • 金属酵素による酸素活性化機構に関する理論的研究

    塩田 淑仁,堀 一則,吉澤 一成

    分子科学討論会  2010.9 

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    Event date: 2011.9

    Presentation type:Oral presentation (general)  

    Venue:大阪   Country:Japan  

  • Theoretical Study of the Mechanism of Valence Tautomerism in Cobalt Complexes International conference

    塩田淑仁 佐藤大介 ゲルゲイ・ユハース 吉澤一成

    第7回理論化学物理国際会議  2011.9 

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    Event date: 2011.9

    Presentation type:Oral presentation (general)  

    Venue:東京   Country:Japan  

    I. Introduction
    Valence tautomeric (VT) complexes have attracted much attention recently because of their possible application as new molecular devices like memory or display devices. VT complexes show a ligand-metal electron transfer coupled with a spin change on the central metal ion, which can be switched by external stimuli like light, heat, or pressure. We use a model for the cobalt bis(quinone) complex [CoIII(3,5-dbcat)(3,5-dbsq)(bpy)] (cat: catecholate, sq: semiquinon, and bpy: 2,2’-bipyridine), which was first reported by Buchanan and Pierpont in 1980. The complex is in the CoIII-LS form (LS: low-spin doublet state) below 273 K, and the population of the CoII-HS form (HS: high-spin sextet state) starts with increasing temperature.
    II. Method of calculation
    Energy calculations for the [CoII-HS(sq)2(bpy)] and [CoIII-LS(sq)(cat)(bpy)] complexes in the doublet, quartet, and sextet spin states were carried out by using the B3LYP* functional (with 15% Hartree–Fock exchange) implemented in the program packages Gaussian 03 and GAMESS. For the Co atom, the (14s9p5d)/[9s5p3d] primitive set of Wachters-Hay with one polarization f-function (α = 1.117) and for the H, C, N, and O, the 6-311G** basis set were used.
    III. Results and discussions
    Valence tautomerism is studied in [CoII-HS(sq)2(bpy)]/[CoIII-LS(sq)(cat)(bpy)] mononuclear cobalt complex by using DFT methods. Calculations at the B3LYP* level of theory reproduce well the energy gap between the CoII-HS and CoIII-LS forms, giving an energy gap of 4.4 kcal/mol, which is comparable to an experimental value of 8.9 kcal/mol. Potential energy surfaces and crossing seams of the electronic states of the doublet, quartet, and sextet spin states are calculated along minimum energy paths connecting the energy minima corresponding to the different spin states. Calculated minimum energy crossing points (MECPs) are located 8.8 kcal/mol in the doublet/sextet surface, 10.2 kcal/mol in the doublet/quartet surface, and 8.4 kcal/mol in the quartet/sextet surface relative to the doublet ground state. Considering the energy of the three spin states and the crossing points, the one-step relaxation between the CoII-HS and CoIII-LS forms is the most probable. This research shows that mapping MECPs can be a useful strategy to analyze the potential energy surfaces of systems with complex deformation modes.

  • Co 錯体の原子価互変異性に関する理論 的研究

    塩田淑仁・佐藤大介・ゲルゲイ ユハース・吉澤一成

    日本化学会  2011.3 

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    Event date: 2011.3

    Presentation type:Oral presentation (general)  

    Venue:東京   Country:Japan  

    Valence tautomerism is studied in [CoII-HS(sq)2(bpy)]/[CoIII-LS(sq)(cat)(bpy)] mononuclear cobalt complex by using DFT methods (HS: high spin, LS: low spin, cat: catecholate, sq: semiquinon, and bpy: 2,2'-bipyridine). Calculations at the B3LYP* level of theory reproduce well the energy gap between the CoII-HS and CoIII-LS forms giving an energy gap of 4.4 kcal/mol, which is comparable to the experimental value of 8.9 kcal/mol.

  • Theoretical study of methane-to-methanol conversion by pMMO International conference

    塩田淑仁 ゲルゲイ・ユハース 吉澤一成

    第一回統合物質国際シンポジウム  2011.1 

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    Event date: 2011.1

    Presentation type:Oral presentation (general)  

    Venue:札幌   Country:Japan  

    A new mechanism for methane hydroxylation by particulate methane monooxygenase (pMMO) is proposed by using QM/MM calculations on the basis of the X-ray crystal structure analysis of pMMO. Important roles of the dicopper active site for methane hydroxylation are discussed. In the initial stages of the reaction substrate methane comes into contact with the mixed-valent bis(μ-oxo)CuIICuIII active center and then a C-H bond of methane is cleaved by one of the oxo species with the formation of an O-H bond. At the same time, the resulting methyl radical species is bound to one of the copper ions. The migration of the methyl ligand to the other bridging oxo ligand occurs in the next step, instead of the direct CH3 and OH recombination that is expected to occur in the oxygen rebound mechanism. Finally methanol is formed as a result of the recombination of the hydroxo hydrogen and the methoxy ligand. The initial H-atom abstraction step is the rate-determining step in the computed reaction pathway. The computational result is consistent with observed kinetic isotope effects.

  • 高原子価金属オキソ種の電子状態とその反応性に関する量子化学計算 Invited

    塩田淑仁

    計算化学談話会  2011.1 

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    Event date: 2011.1

    Presentation type:Oral presentation (general)  

    Venue:福岡   Country:Japan  

  • Theoretical Study of Spin Transition between the Singlet State and the Quintet State in the [Fe(2-pic)3]2+ Spin Crossover System (2-pic: 2-picolylamine) International conference

    塩田淑仁 佐藤大介 ゲルゲイ ユハース 吉澤一成

    第60回記念錯体化学OSAKA国際会議  2010.9 

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    Event date: 2010.9

    Presentation type:Oral presentation (general)  

    Venue:大阪   Country:Japan  

  • 金属錯体のスピン交差に関する理論的研究

    塩田淑仁 佐藤大介 ゲルゲイ ユハース 吉澤一成

    理論化学討論会  2010.5 

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    Venue:札幌   Country:Japan  

  • ベンゼン水酸化反応における鉄活性点とゼオライト反応場の理論的解析

    塩田淑仁 鈴木邦彦 吉澤一成

    分子構造総合討論会  2006.9 

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    Venue:静岡   Country:Japan  

  • Fe-ZSM-5ゼオライト細孔内のベンゼンの挙動に関する理論的研究

    鈴木邦彦 塩田淑仁 吉澤一成

    分子構造総合討論会  2006.9 

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    Venue:静岡   Country:Japan  

  • ゼオライト触媒によるMTE反応に関する理論的解析

    井上俊徳 塩田淑仁 吉澤一成

    分子構造総合討論会  2006.9 

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    Venue:静岡   Country:Japan  

  • Fe-ZSM-5ゼオライト細孔内におけるベンゼンの反応性に関する理論的研究

    鈴木邦彦 塩田淑仁 吉澤一成

    西日本化学会  2006.9 

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    Venue:沖縄   Country:Japan  

  • FER型ゼオライトによるMTE反応に関する理論的解析

    井上俊徳 塩田淑仁 吉澤一成

    西日本化学会  2006.9 

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    Venue:沖縄   Country:Japan  

  • QM/MM法によるベンゼン水酸化反応の理論的解明

    塩田淑仁 鈴木邦彦 吉澤一成

    触媒討論会  2006.9 

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    Presentation type:Oral presentation (general)  

    Venue:富山   Country:Japan  

  • ゼオライト触媒によるベンゼンの水酸化反応に関する理論的解析

    鈴木邦彦 塩田淑仁 吉澤一成

    触媒討論会  2006.9 

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    Venue:富山   Country:Japan  

  • ゼオライト触媒によるメタノール-エチレン転化反応に関する理論的解明

    井上俊徳 塩田淑仁 吉澤一成

    触媒討論会  2006.9 

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    Venue:富山   Country:Japan  

  • QM/MM法によるベンゼン水酸化反応の理論的研究

    塩田淑仁 鈴木邦彦 吉澤一成

    西日本化学会  2006.11 

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    Venue:沖縄   Country:Japan  

  • 二核銅錯体によるC-H結合活性化に関する理論的研究

    塩田淑仁 吉澤一成

    日本化学会  2007.3 

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    Venue:大阪   Country:Japan  

  • メタン酸化酵素の銅二核中心に関する理論的研究

    塩田淑仁 吉澤一成

    分子科学会  2008.10 

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    Presentation type:Oral presentation (general)  

    Venue:福岡   Country:Japan  

  • 理論化学は酵素反応をどこまで明らかにできるのか? -数原子のモデルから数万原子の現実系への拡張- Invited

    塩田淑仁

    分子科学会  2008.12 

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    Presentation type:Symposium, workshop panel (public)  

    Venue:福岡   Country:Japan  

  • 銅二核活性点によるC-H結合活性化の触媒機構に関する理論的研究

    塩田淑仁 吉澤一成

    日本化学会春季年会  2009.3 

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    Venue:福岡   Country:Japan  

  • 銅二核活性点をもつ酵素の触媒機構に関する理論的研究 Invited

    塩田淑仁 吉澤一成

    理論化学討論会  2009.5 

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    Presentation type:Symposium, workshop panel (public)  

    Venue:東京   Country:Japan  

  • 膜結合型メタンモノオキシゲナーゼの銅活性点に関する理論的研究

    塩田淑仁 堀一則 吉澤一成

    分子科学会  2009.9 

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    Presentation type:Oral presentation (general)  

    Venue:名古屋   Country:Japan  

  • 二核銅活性点を有するメタン酸化酵素のQM/MM計算

    塩田淑仁 堀一則 吉澤一成

    日本化学会春季年会  2010.3 

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    Presentation type:Oral presentation (general)  

    Venue:大阪   Country:Japan  

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MISC

  • 超次元マテリアルの理論設計 Reviewed

    塩田 淑仁

    セラミクス 55 (2020) 575   2020.5

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    Language:Japanese   Publishing type:Article, review, commentary, editorial, etc. (scientific journal)  

    量子化学計算は原子配列を元にそこに存在する電子 のエネルギーを計算し,さらに核配置を最適化するこ とでその物質の構造と電子状態を求める方法である. これらの方法は今までに孤立分子や周期系の固体に適 用され,その有効性が確かめられてきた.計算能力向 上によって大きな系へ適用できるようになり,欠陥や 不純物などを含む不均一な系においてもある程度定量 的な評価が可能となった.その結果,特異な構造を有 する材料の解析も工夫次第でアプローチできるように なりつつある.

  • Effect of Multi Copper Complexes on the Alkane Oxidation with H<sub>2</sub>O<sub>2</sub>

    藤川恭祐, 田中皐晴, 人見穣, 小寺政人, 吉澤一成, 塩田淑仁, 亀谷陽平

    酸化反応討論会講演要旨集   55th   2022

  • 銅2核錯体によるC‐H結合活性化に関する理論的研究

    塩田淑仁, 堀優太, 小寺政人, 吉澤一成

    日本化学会春季年会講演予稿集(CD-ROM)   2018.3

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    銅2核錯体によるC‐H結合活性化に関する理論的研究

  • 酸化還元活性な配位子を有する鉄錯体の高酸化状態における電子構造

    西部貴久, 荻島郁弥, 小谷弘明, 石塚智也, 岡島敏浩, 野澤俊介, 塩田淑仁, 吉澤一成, 小島隆彦

    錯体化学会討論会講演要旨集   2017.9

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    酸化還元活性な配位子を有する鉄錯体の高酸化状態における電子構造

  • 大環状アニオン性配位子を有する鉄錯体の高酸化状態における電子構造

    西部貴久, 荻島郁弥, 小谷弘明, 石塚智也, 岡島敏浩, 野澤俊介, 塩田淑仁, 吉澤一成, 小島隆彦

    錯体化学会討論会講演要旨集   2016.8

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    大環状アニオン性配位子を有する鉄錯体の高酸化状態における電子構造

  • Role of tyrosine residue in methane activation by pMMO

    K. Yoshizawa, Y. Shiota, G. Juhasz

    JOURNAL OF BIOLOGICAL INORGANIC CHEMISTRY   2014.3

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  • メタン活性化—電子状態理論からのアプローチ-

    塩田 淑仁

    触媒   2013.6

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    Theoretical study of methane activation catalyzed by transition metal-oxo species Yoshihito SHIOTA (Institute for materials chemistry and engineering, Kyushu University, Motooka, Nishi-ku, Fukuoka 819-0395, Japan)
    Reaction pathways and energetics for the conversion of methane to methanol by the bare FeO+ ion, the FeO+ species over Fe-ZSM-5, and the dicopper species of pMMO are discussed using density-functional-theory calculations. Computed reaction pathway is a non-radical mechanism to form a hydroxo intermediate, HO–M+–CH3, via H-atom abstraction with a four-centered transition state, which occurs at a coordinatively unsaturated metal center. A detailed analysis of the potential energy surfaces shows that crossing between high-spin and low-spin potential energy surfaces occurs twice in the entrance channel and in the exit channel in FeO+.

  • A theoretical study of the mononuclear non-hem iron complex of phenylalanine hydroxylase (PAH)

    Y Shiota, K Yoshizawa

    JOURNAL OF INORGANIC BIOCHEMISTRY   2003.7

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  • A theoretical study of the dynamical aspects of alkane hydroxylation by compound I of cytochrome p450

    K Yoshizawa, T Kamachi, Y Shiota

    JOURNAL OF INORGANIC BIOCHEMISTRY   2001.8

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  • Methane-methanol conversion by MnO+, FeO+, and CoO+: A theoretical study of catalytic selectivity

    K Yoshizawa, Y Shiota, T Yamabe

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   1998.1

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    The entire reaction pathway for the gas-phase methane-methanol conversion by late transition-metal-oxide ions, MnO+, FeO+, and CoO+, is studied using an ab initio hybrid (Hartree-Fock/density-functional) method. For these oxo complexes, the methane-methanol conversion is proposed to proceed via two transition states (TSs) in such a way MO+ + CH4 --> OM+(CH4) --> [TS1] --> HO-M+-CH3 --> [TS3] --> M+(CH3OH) --> M+ + CH3OH, where M is Mn, Fe, and Co. A crossing between high-spin and low-spin potential energy surfaces occurs both at the entrance channel and at the exit channel for FeO+ and CoO+, but it occurs only once near TS2 for MnO+. The activation energy from OMn+(CH4) to HO-Mn+-CH3 via TS1 is calculated to be 9.4 kcal/mol, being much smaller than 22.1 and 30.9 kcal/mol for FeO+ and CoO+, respectively. This agrees with the experimentally reported efficiencies for the reactions. The excellent agreement between theory and experiment indicates that HO-M+-CH3 plays a central role as an intermediate in the reaction between MO+ and methane and that the reaction efficiency is most likely to be determined by the activation energy from OM+(CH4) to HO-M+-CH3 via TS1. We discuss in terms of qualitative orbital interactions why MnO+ (d(4) oxo complex) is most effective for methane C-H bond activation. The activation energy from HO-M+-CH3 to M+(CH3OH) via TS2 is computed to be 24.6, 28.6, and 35.9 kcal/mol for CoO+, FeO+, and MnO+, respectively. This result explains an experimental result that the methanol-branching ratio in the reaction between MO+ and methane is 100&#37; in CoO+, 41&#37; in FeO+, and < 1&#37; in MnO+. We demonstrate that both the barrier heights of TS1 and TS2 would determine general catalytic selectivity for the methane-methanol conversion by the MO+ complexes.

    DOI: 10.1021/ja971723u

  • Orbital interaction and vibrational mode analyses for phase transitions of BaTiO3

    T Takeuchi, K Yoshizawa, Y Shiota, O Nakamura, H Kageyama, T Yamabe

    JOURNAL OF MATERIALS CHEMISTRY   1997.6

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    The phase transitions of ATiO(3)-type perovskite structures, mainly those of barium titanate (BaTiO3), aro studied theoretically in terms of orbital interactions and vibrational modes. Vibrational analyses for fundamental TiO6 clusters, up to Ti8O36, are performed with a hybrid (Hartree-Fock/density functional) method. Important structural distortions from the high symmetry cubic phase are rationalized by a second-order perturbational treatment of quantum chemistry. The orbital symmetry argument based on group theory indicates that the transition density around frontier molecular orbitals plays an important role in the motions of ions at the transition temperatures. Our orbital interaction and vibrational mode analyses of the phase transitions are consistent with the soft mode theory of Cochran.

    DOI: 10.1039/a607475h

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Professional Memberships

  • 日本化学会

  • 触媒学会

  • 日本コンピューター化学会

  • Japan Society of Molecular Science

  • Society of Biological Inorganic Chemistry

  • コンピュータ化学会

  • JAPAN SOCIETY FOR MOLECULAR SCIENCE

  • 日本化学会

  • 生物無機化学会

  • 触媒学会

  • 触媒学会

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  • 日本化学会

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  • JAPAN SOCIETY FOR MOLECULAR SCIENCE

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  • コンピュータ化学会

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Academic Activities

  • 実行委員

    分子科学会  ( Japan ) 2018.9

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    Number of participants:1,200

  • Screening of academic papers

    Role(s): Peer review

    2017

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    Type:Peer review 

    Number of peer-reviewed articles in foreign language journals:10

  • 実行委員 International contribution

    藤原セミナー  ( Japan ) 2016.4

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    Number of participants:200

  • 実行委員 International contribution

    第70回藤原セミナー  ( Japan ) 2016.4

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    Number of participants:100

  • 実行委員

    九重分子科学セミナー2015  ( Japan ) 2015.7

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    Number of participants:50

  • 座長(Chairmanship)

    41生体分子科学討論会  ( Japan ) 2014.6

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  • 実行委員

    第41回生体分子科学討論会  ( Japan ) 2014.6

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    Number of participants:100

  • 座長(Chairmanship)

    日本化学会第93春季年会(2013)  ( Japan ) 2014.3

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  • 実行委員、総合司会 International contribution

    日仏理論化学シンポ  ( Japan ) 2012.3

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  • 実行委員 International contribution

    日仏理論化学シンポ  ( Japan ) 2012.3

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    Number of participants:50

  • 実行委員

    九重分光セミナー2011  ( Japan ) 2011.7

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    Number of participants:50

  • 座長(Chairmanship)

    日本化学会  ( Japan ) 2011.3 - Present

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  • 座長(Chairmanship)

    日本化学会  ( Japan ) 2011.3 - Present

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  • 座長(Chairmanship)

    分子科学会  ( Japan ) 2010.9

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  • 座長(Chairmanship)

    分子科学会  ( Japan ) 2010.9 - Present

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    日本化学会  ( Japan ) 2010.3 - Present

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  • 実行委員

    第二回分子科学討論会  ( Japan ) 2008.9

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    Number of participants:1,500

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    九重分光セミナー2007  ( Japan ) 2007.7

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  • 実行委員

    九重分光セミナー2007  ( Japan ) 2007.7

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    Number of participants:50

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    日本化学会  ( Japan ) 2003.4 - Present

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Research Projects

  • 計算科学による触媒インフォマティクスの開拓

    Grant number:24K21245  2024.6 - 2029.3

    Grants-in-Aid for Scientific Research  Grant-in-Aid for Challenging Research (Pioneering)

    吉澤 一成, 塩田 淑仁

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    Grant type:Scientific research funding

    触媒反応に関する網羅的な第一原理計算とその結果を機械学習から再構築する触媒インフォマティクスを立ち上げ、それをさまざまな触媒系に応用展開することである。代表者は、酵素を含む均一系触媒および不均一系触媒や接着界面相互作用など、これまで電子状態理論が不得手としていた複雑化学系の理論化学研究で多くの成果を挙げている。本研究では、触媒に特化した複雑化学系における理論先導型研究を実施する。安定小分子である窒素、メタン、二酸化炭素の有効利用を図るための触媒開発を行うとともに、計算科学に基づく触媒インフォマティクスを確立し、それをさまざまな触媒系に応用展開する。

    CiNii Research

  • 鉄と銅を基軸とした酸素活性化触媒の理論研究

    Grant number:16K05725  2016 - 2019

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

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    Authorship:Principal investigator  Grant type:Scientific research funding

  • CREST革新的触媒

    2015.10 - 2020.3

    九州大学 JST 

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    Authorship:Collaborating Investigator(s) (not designated on Grant-in-Aid) 

    本研究領域は、多様な天然炭素資源をバランスよく活用できる将来の産業基盤の確立に向けて、その根幹をなすメタンをはじめとするアルカンガス資源を従来にない形で有用な化成品・エネルギーに変換するための革新的な触媒の創出を推進します。
     埋蔵量が豊富な天然ガス等に含まれるメタンをはじめとするアルカンガス資源からこれまでにない技術で化成品やエネルギーへの変換が容易にできるようになれば、現代社会が直面する石油依存という問題からの脱却や二酸化炭素排出低減も可能になります。しかし、メタンなどのアルカンガス資源を直接化成品などに変換するプロセスは難度が高く、メタンの改質によって生成する合成ガス(CO+H2)を経由するなどの間接的なプロセスを利用しているのが現状です。
     この高難度な課題を克服することが本研究領域の主眼であり、高度な触媒技術を生み出す新しい取り組みを推進します。そのためには、近年進化しているデータ科学、計算科学、計測技術などと連携することによって、これまでに蓄積された触媒に関する経験知を非連続的に飛躍させることが重要です。
     本研究領域では、特に難度が高いメタンを反応基質とする研究を基軸に据えます。エタンやプロパン等の低級アルカンを反応基質とする反応については、既知の手法に比較して圧倒的に高活性・高選択性を目指す革新的な触媒研究を対象とします。
     将来的に、化学産業における天然ガス等の資源の新たな活用を切り開き、ひいては新たな産業基盤の確立につながる、本格的にして世界をリードできる触媒研究を推進します。

  • 統合物質創製化学推進事業

    2015.4 - 2020.3

    九州大学 名古屋大学 京都大学 北海道大学 

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    Authorship:Coinvestigator(s) 

    現代の最先端学術研究は益々学際化しており、革新的な物質創製を実現するためには、複数研究分野の有機的連携が必要不可欠である。すなわち、それぞれに特徴ある世界水準の研究活動を展開してきた研究機関といえども、多種多様なすべての物質様式を包含することは困難であり、特徴ある物質創製研究を推進している他大学機関との連携を図ることが是非とも必要である。物質創製における我が国の優位性を確固たるものにし、次世代の物質文明の基盤を支えるためにも、各グループがもつ化学研究の力量を結集できる、実践的な機関連携研究組織の構築を迅速に行なわなければならない。

     このような背景のもと、物質階層を構成する「元素」(京都大学化学研究所附属元素科学国際研究センター)、「分子」(名古屋大学物質科学国際研究センター)、「集合体」(九州大学先導物質化学研究所)の研究を融合するべく、大学間連携研究「物質合成研究拠点機関連携事業」(H17〜21年度)を実施した。これは本事業の基礎となるもので、各物質階層を縦断する新物質の合成と新機能の開拓において卓越した研究成果を挙げ、また有為な人材を多数輩出することにも成功した。本事業では、各物質階層における化学研究の融合を踏まえ、「物理的物質合成概念」および「生命物質合成概念」をも包含する新たな「化学物質変換概念」を創出し、統合的な物質創製化学を実践する。あらゆる物質階層における物質変換概念において「触媒」が一つの共通キーワードとなるため、触媒研究の国際研究拠点である北海道大学触媒化学研究センターをこの組織に加え、連携研究体制を強化・充実させた。特に、北海道大学触媒化学研究センターが得意とする固体触媒は、緊迫するエネルギー環境問題解決に必要不可欠な研究要素であり、4研究機関の有機的連携により、最先端バイオ・情報技術からエネルギー・環境問題にまで至る、新物質・新反応・新機能の開拓に、総合的観点から取り組むことのできる、強力な研究組織が整備される。研究機関間の緩やかな連携は欧米先進諸国でも実施されているが、それらの多くは特定テーマに限定的である。物質創製化学研究を革新し、異なる物質階層および異なった物質変換概念を包括的に推進する本連携事業は他に類例を見ないものである。

  • 酵素触媒反応の原動力となる金属活性種と量子化学計算の新展開

    Grant number:25410071  2013 - 2015

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

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    Authorship:Principal investigator  Grant type:Scientific research funding

  • 酵素触媒反応の原動力となる金属活性種と量子化学計算の新展開

    Grant number:25410071  2013 - 2015

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

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    Authorship:Principal investigator  Grant type:Scientific research funding

  • 基質感応性化学種の電子状態とその変化に関する理論的研究

    2012 - 2016

    Japan Society for the Promotion of Science・Ministry of Education, Culture, Sports, Science and Technology  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research on Innovative Areas

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    Authorship:Collaborating Investigator(s) (not designated on Grant-in-Aid)  Grant type:Scientific research funding

  • 配位ナノクラスターの精密設計に基づく外場応答新物質群の創出

    2011

    Grants-in-Aid for Scientific Research  平成23年度募集第1期CREST

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    Authorship:Coinvestigator(s)  Grant type:Competitive funding other than Grants-in-Aid for Scientific Research

  • 統合物質創製化学推進事業

    2010.4 - 2015.3

    九州大学 名古屋大学 京都大学 北海道大学 

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    Authorship:Coinvestigator(s) 

    現代の最先端学術研究は益々学際化しており、革新的な物質創製を実現するためには、複数研究分野の有機的連携が必要不可欠である。すなわち、それぞれに特徴ある世界水準の研究活動を展開してきた研究機関といえども、多種多様なすべての物質様式を包含することは困難であり、特徴ある物質創製研究を推進している他大学機関との連携を図ることが是非とも必要である。物質創製における我が国の優位性を確固たるものにし、次世代の物質文明の基盤を支えるためにも、各グループがもつ化学研究の力量を結集できる、実践的な機関連携研究組織の構築を迅速に行なわなければならない。

     このような背景のもと、物質階層を構成する「元素」(京都大学化学研究所附属元素科学国際研究センター)、「分子」(名古屋大学物質科学国際研究センター)、「集合体」(九州大学先導物質化学研究所)の研究を融合するべく、大学間連携研究「物質合成研究拠点機関連携事業」(H17〜21年度)を実施した。これは本事業の基礎となるもので、各物質階層を縦断する新物質の合成と新機能の開拓において卓越した研究成果を挙げ、また有為な人材を多数輩出することにも成功した。本事業では、各物質階層における化学研究の融合を踏まえ、「物理的物質合成概念」および「生命物質合成概念」をも包含する新たな「化学物質変換概念」を創出し、統合的な物質創製化学を実践する。あらゆる物質階層における物質変換概念において「触媒」が一つの共通キーワードとなるため、触媒研究の国際研究拠点である北海道大学触媒化学研究センターをこの組織に加え、連携研究体制を強化・充実させた。特に、北海道大学触媒化学研究センターが得意とする固体触媒は、緊迫するエネルギー環境問題解決に必要不可欠な研究要素であり、4研究機関の有機的連携により、最先端バイオ・情報技術からエネルギー・環境問題にまで至る、新物質・新反応・新機能の開拓に、総合的観点から取り組むことのできる、強力な研究組織が整備される。研究機関間の緩やかな連携は欧米先進諸国でも実施されているが、それらの多くは特定テーマに限定的である。物質創製化学研究を革新し、異なる物質階層および異なった物質変換概念を包括的に推進する本連携事業は他に類例を見ないものである。

  • 量子化学計算による人工変異酵素の設計と反応制御

    Grant number:22245028  2010 - 2013

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

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    Authorship:Collaborating Investigator(s) (not designated on Grant-in-Aid)  Grant type:Scientific research funding

  • 量子化学計算による人工変異酵素の設計と反応制御

    Grant number:22245028  2010 - 2013

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (A)

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    Authorship:Coinvestigator(s)  Grant type:Scientific research funding

  • ナノバイオセンシング用フォトニクス材料群の合成 提案者: 徳田陽明(京大化研・助教) 塩田淑仁(九大先導研・助教) 必要経費(京大分):150 万円(内訳、次頁の通り) バイオテクノロジーにおいては精緻な状態分析法が 技術の発達を促してきた。例えば、タンパク質の蛍光標 識技術の進展がバイオテクノロジーの発達を促し、新た な機能理解、新薬創製、難病の克服につながったことは いうまでもない。生体物質の状態・構造をありのままに 観察することと、その機能理解・応用は車の両輪のよう なものであり、精密な状態観察法に対する要求が高まり つつある。 生体物質の反応の場としては液体内、固体内、固/液、 固/気の界面が重要となる。例えば花粉症に代表される ようなアレルギー反応においては、血液中の抗体が抗原 を化学認識する。また代謝においては化学ポテンシャル が細胞内で形成され、反応が進行することが知られてい る。このような反応の評価は、例えばタンパク質発現量 の評価などといった現象論的方法によって行われてきた。 これにより得られるパラメータは、個々の生体物質の振 る舞いを統計的に丸め込んだものである。本研究では生 体物質の1 分子認識を究極目標とし、ナノバイオセンシン グ用フォトニクス材料群を合成し、その評価を行う。

    2010 - 2011

    京都大学化学研究所 大学間連携拠点経費

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    Authorship:Principal investigator  Grant type:Contract research

  • 銅タンパク質による酸素活性化と量子化学計算の新展開

    Grant number:21750063  2009 - 2012

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

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    Authorship:Principal investigator  Grant type:Scientific research funding

  • 銅タンパク質による酸素活性化と量子化学計算の新展開

    Grant number:21750063  2009 - 2012

    Grants-in-Aid for Scientific Research  Grant-in-Aid for Young Scientists (B)

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    Authorship:Principal investigator  Grant type:Scientific research funding

  • ナノバイオセンシング用フォトニクス材料群の合成 提案者: 徳田陽明(京大化研・助教) 塩田淑仁(九大先導研・助教) 必要経費(京大分):150 万円(内訳、次頁の通り) バイオテクノロジーにおいては精緻な状態分析法が 技術の発達を促してきた。例えば、タンパク質の蛍光標 識技術の進展がバイオテクノロジーの発達を促し、新た な機能理解、新薬創製、難病の克服につながったことは いうまでもない。生体物質の状態・構造をありのままに 観察することと、その機能理解・応用は車の両輪のよう なものであり、精密な状態観察法に対する要求が高まり つつある。 生体物質の反応の場としては液体内、固体内、固/液、 固/気の界面が重要となる。例えば花粉症に代表される ようなアレルギー反応においては、血液中の抗体が抗原 を化学認識する。また代謝においては化学ポテンシャル が細胞内で形成され、反応が進行することが知られてい る。このような反応の評価は、例えばタンパク質発現量 の評価などといった現象論的方法によって行われてきた。 これにより得られるパラメータは、個々の生体物質の振 る舞いを統計的に丸め込んだものである。本研究では生 体物質の1 分子認識を究極目標とし、ナノバイオセンシン グ用フォトニクス材料群を合成し、その評価を行う。

    2009

    京都大学化学研究所 大学間連携拠点経費

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    Authorship:Principal investigator  Grant type:Contract research

  • 動的キラリティー制御を基盤とする新規キラルシステムの開発:らせんダイナミクスと分子素子機能   本研究は動的にキラルな「らせん状分子」のダイナミクスに関する新現象の探索と,これを活用した高機能不斉素子の開発をおこなうことにより,動的キラリティーの制御と機能化の新たな方法論を確立してキラルケミストリーに学術的新機軸をもたらすことを目的とする.   具体的には動的な軸性キラリティーを有し.二次構造としてらせん構造をとるポリアリール分子を設計・合成する.これらに関して,構造有機化学的アプローチからのダイナミクスに関する研究,および有機合成化学的に有用な機能の調査をおこない,得られた成果を量子化学計算と統合,発展させ,新しいキラルシステムの開発を目指す.

    2008

    拠点内科研費 G-COE 若手科研費

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    Authorship:Coinvestigator(s)  Grant type:Contract research

  • 量子化学計算による生物無機化学の新たな展開

    Grant number:18350088  2006 - 2008

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

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    Grant type:Scientific research funding

  • 量子化学計算による生物無機化学の新たな展開

    Grant number:18350088  2006 - 2008

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (B)

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    Authorship:Coinvestigator(s)  Grant type:Scientific research funding

  • 大学間連携研究

    2005.6 - 2009.3

    九州大学 名古屋大学 京都大学 

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    Authorship:Coinvestigator(s) 

    この事業はあらゆる基礎学問の進歩と新技術開発の基盤となる「物質合成研究」において世界をリードするための新たな機関連携研究体制を構築することを目的として、平成17年4月から、文部科学省特別教育研究経費(大学間連携経費)により、京都大学化学研究所附属元素科学国際研究センター、名古屋大学物質科学国際研究センター、九州大学先導物質化学研究所が中心となり、3大学により開始されたもので、5年の事業期間が予定されています。また、これは約10年前に、名古屋大学、九州大学、京都大学にて順次発足した中核的研究拠点(COE)形成プログラムの研究グループが連携し、各拠点のこれまでの成果を基に物質合成研究の中核的研究拠点の中の「中核」を形成しようとするもので、目標達成に向けて、各大学に連携推進ラボを設置して「組織横断型研究課題」と若手研究者が提案する「テーマ提案型研究課題」を実施します。さらに、大学院生を含む若手研究者の育成も同事業の重要課題の一つとして推進され、幅広い知識と複眼的思考を備えた次世代を担う人材を育成します。

  • 環境ナノ触媒

    2003.4

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    Authorship:Coinvestigator(s) 

  • ナノテクノロジー支援

    2002.10

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    Authorship:Coinvestigator(s) 

  • 大規模密度汎関数計算による生体化学反応へのアプローチ

    Grant number:14390039  2002 - 2004

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

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    Authorship:Collaborating Investigator(s) (not designated on Grant-in-Aid)  Grant type:Scientific research funding

  • 大規模密度汎関数計算による生体化学反応へのアプローチ

    Grant number:14390039  2002 - 2004

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (B)

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    Authorship:Coinvestigator(s)  Grant type:Scientific research funding

  • 金属酸化物による炭素-水素結合活性化に関する理論的研究

    1996 - 2003

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

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    Grant type:Scientific research funding

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Class subject

  • 機能物質化学講究G

    2024.4 - 2025.3   Full year

  • 分子電子構造論

    2024.4 - 2024.9   First semester

  • Molecular Electronic Structures

    2024.4 - 2024.9   First semester

  • 量子化学演習

    2023.12 - 2024.2   Winter quarter

  • 量子化学演習

    2023.12 - 2024.2   Winter quarter

  • 量子化学演習

    2023.12 - 2024.2   Winter quarter

  • 触媒化学

    2023.10 - 2023.12   Fall quarter

  • 触媒化学

    2023.10 - 2023.12   Fall quarter

  • 分子電子構造論

    2023.4 - 2023.9   First semester

  • 分子電子構造論

    2023.4 - 2023.9   First semester

  • Molecular Electronic Structures

    2023.4 - 2023.9   First semester

  • 量子化学演習

    2022.12 - 2023.2   Winter quarter

  • 量子化学演習

    2022.12 - 2023.2   Winter quarter

  • 分子電子構造論

    2022.4 - 2022.9   First semester

  • Molecular Electronic Structures

    2022.4 - 2022.9   First semester

  • Molecular Electronics

    2022.4 - 2022.9   First semester

  • 分子電子構造論

    2022.4 - 2022.9   First semester

  • 量子化学演習

    2021.12 - 2022.2   Winter quarter

  • 量子化学第一

    2021.12 - 2022.2   Winter quarter

  • 量子化学演習

    2021.12 - 2022.2   Winter quarter

  • 量子化学第一

    2021.12 - 2022.2   Winter quarter

  • 量子化学演習

    2021.12 - 2022.2   Winter quarter

  • 量子化学

    2021.12 - 2022.2   Winter quarter

  • 分子電子構造論

    2021.4 - 2021.9   First semester

  • 分子電子構造論

    2021.4 - 2021.9   First semester

  • Molecular Electronics

    2021.4 - 2021.9   First semester

  • 2年生学生実験

    2021.4 - 2021.9   First semester

  • Molecular Electronics

    2021.4 - 2021.9   First semester

  • 3年生学生実験

    2021.4 - 2021.9   First semester

  • 量子化学

    2020.12 - 2021.2   Winter quarter

  • 量子化学演習

    2020.12 - 2021.2   Winter quarter

  • 量子化学演習

    2020.12 - 2021.2   Winter quarter

  • 分子分光学演習

    2020.12 - 2021.2   Winter quarter

  • 量子化学演習

    2020.12 - 2021.2   Winter quarter

  • 分子分光学演習

    2020.12 - 2021.2   Winter quarter

  • 分子電子構造論

    2020.4 - 2020.9   First semester

  • 3年生学生実験

    2020.4 - 2020.9   First semester

  • 分子電子構造論

    2020.4 - 2020.9   First semester

  • Molecular Electronics

    2020.4 - 2020.9   First semester

  • 2年生学生実験

    2020.4 - 2020.9   First semester

  • Molecular Electronics

    2020.4 - 2020.9   First semester

  • 量子化学演習

    2019.12 - 2020.2   Winter quarter

  • 量子化学演習

    2019.12 - 2020.2   Winter quarter

  • 分子分光学演習

    2019.12 - 2020.2   Winter quarter

  • 量子化学演習

    2019.12 - 2020.2   Winter quarter

  • 量子化学

    2019.12 - 2020.2   Winter quarter

  • 分子電子構造論

    2019.4 - 2019.9   First semester

  • 2年生学生実験

    2019.4 - 2019.9   First semester

  • Molecular Electronics

    2019.4 - 2019.9   First semester

  • 3年生学生実験

    2019.4 - 2019.9   First semester

  • 量子化学第一

    2018.12 - 2019.2   Winter quarter

  • 量子化学

    2018.10 - 2019.3   Second semester

  • 量子化学演習

    2018.10 - 2019.3   Second semester

  • 量子化学演習

    2018.10 - 2019.3   Second semester

  • 分子電子構造論

    2018.4 - 2018.9   First semester

  • 2年生学生実験

    2018.4 - 2018.9   First semester

  • Molecular Electronics

    2018.4 - 2018.9   First semester

  • 3年生学生実験

    2018.4 - 2018.9   First semester

  • 量子化学

    2017.10 - 2018.3   Second semester

  • 量子化学第一

    2017.10 - 2018.3   Second semester

  • 量子化学演習

    2017.10 - 2018.3   Second semester

  • 量子化学演習

    2017.10 - 2018.3   Second semester

  • 分子電子構造論

    2017.4 - 2017.9   First semester

  • 2年生学生実験

    2017.4 - 2017.9   First semester

  • Molecular Electronics

    2017.4 - 2017.9   First semester

  • 3年生学生実験

    2017.4 - 2017.9   First semester

  • 量子化学

    2016.10 - 2017.3   Second semester

  • 分子電子構造論

    2016.4 - 2016.9   First semester

  • 2年生学生実験

    2016.4 - 2016.9   First semester

  • 3年生学生実験

    2016.4 - 2016.9   First semester

  • 量子化学

    2015.10 - 2016.3   Second semester

  • 分子電子構造論

    2015.4 - 2015.9   First semester

  • 2年生学生実験

    2015.4 - 2015.9   First semester

  • 3年生学生実験

    2015.4 - 2015.9   First semester

  • 量子化学

    2014.10 - 2015.3   Second semester

  • 3年生学生実験

    2014.4 - 2014.9   First semester

  • 2年生学生実験

    2014.4 - 2014.9   First semester

  • グリーンケミストリー

    2013.4 - 2013.9   First semester

  • 2年生学生実験

    2013.4 - 2013.9   First semester

  • 3年生学生実験

    2013.4 - 2013.9   First semester

  • グリーンケミストリー

    2012.4 - 2012.9   First semester

  • 2年生学生実験

    2012.4 - 2012.9   First semester

  • コアセミナー

    2012.4 - 2012.9   First semester

  • 3年生学生実験

    2012.4 - 2012.9   First semester

  • グリーンケミストリー

    2011.4 - 2011.9   First semester

  • 2年生学生実験

    2011.4 - 2011.9   First semester

  • コアセミナー

    2011.4 - 2011.9   First semester

  • 3年生学生実験

    2011.4 - 2011.9   First semester

  • グリーンケミストリー

    2010.4 - 2010.9   First semester

  • 2年生学生実験

    2010.4 - 2010.9   First semester

  • 3年生学生実験

    2010.4 - 2010.9   First semester

  • グリーンケミストリー

    2010.4 - 2010.9   First semester

  • コアセミナー

    2010.4 - 2010.9   First semester

  • コアセミナー

    2010.4 - 2010.9   First semester

  • 2年生学生実験

    2009.10 - 2010.3   Second semester

  • グリーンケミストリー

    2009.4 - 2009.9   First semester

  • グリーンケミストリー

    2009.4 - 2009.9   First semester

  • コアセミナー

    2009.4 - 2009.9   First semester

  • 3年生学生実験

    2009.4 - 2009.9   First semester

  • コアセミナー

    2009.4 - 2009.9   First semester

  • グリーンケミストリー

    2008.4 - 2008.9   First semester

  • グリーンケミストリー

    2008.4 - 2008.9   First semester

  • コアセミナー

    2008.4 - 2008.9   First semester

  • 2年生学生実験

    2007.10 - 2008.3   Second semester

  • 創造工学演習

    2007.4 - 2007.9   First semester

  • 創造工学演習

    2007.4 - 2007.9   First semester

  • 3年生学生実験

    2007.4 - 2007.9   First semester

  • 3年生学生実験

    2006.4 - 2006.9   First semester

  • 創造工学演習

    2006.4 - 2006.9   First semester

  • 3年生学生実験

    2005.10 - 2006.3   Second semester

  • 3年生学生実験

    2005.4 - 2005.9   First semester

  • 創造工学演習

    2005.4 - 2005.9   First semester

  • 創造工学演習

    2004.4 - 2004.9   First semester

▼display all

FD Participation

  • 2013.5   Role:Participation   Title:先導研FD講演会

    Organizer:[Undergraduate school/graduate school/graduate faculty]

  • 2013.1   Role:Participation   Title:先導研FD講演会

    Organizer:[Undergraduate school/graduate school/graduate faculty]

  • 2012.5   Role:Participation   Title:先導研FD講演会

    Organizer:[Undergraduate school/graduate school/graduate faculty]

  • 2012.1   Role:Participation   Title:先導研FD講演会

    Organizer:[Undergraduate school/graduate school/graduate faculty]

  • 2011.5   Role:Participation   Title:先導研FD講演会

    Organizer:[Undergraduate school/graduate school/graduate faculty]

  • 2011.1   Role:Participation   Title:先導研FD講演会

    Organizer:[Undergraduate school/graduate school/graduate faculty]

  • 2010.5   Role:Speech   Title:先導研FD講演会

    Organizer:[Undergraduate school/graduate school/graduate faculty]

  • 2010.1   Role:Participation   Title:先導研FD講演会

    Organizer:[Undergraduate school/graduate school/graduate faculty]

  • 2009.5   Role:Participation   Title:先導研FD講演会

    Organizer:[Undergraduate school/graduate school/graduate faculty]

  • 2008.5   Role:Participation   Title:先導研FD講演会

    Organizer:[Undergraduate school/graduate school/graduate faculty]

  • 2007.2   Role:Participation   Title:先導研FD講演会

    Organizer:[Undergraduate school/graduate school/graduate faculty]

  • 2005.12   Role:Participation   Title:先導研FD講演会

    Organizer:[Undergraduate school/graduate school/graduate faculty]

  • 2004.12   Role:Participation   Title:先導研FD講演会

    Organizer:[Undergraduate school/graduate school/graduate faculty]

  • 2003.12   Role:Participation   Title:先導研FD講演会

    Organizer:[Undergraduate school/graduate school/graduate faculty]

▼display all

Visiting, concurrent, or part-time lecturers at other universities, institutions, etc.

  • 2016  鹿児島大学理工学部  Classification:Part-time lecturer  Domestic/International Classification:Japan 

    Semester, Day Time or Duration:前期

  • 2015  九州地区国立大学 技術職員スキルアップセミナー  Classification:Intensive course  Domestic/International Classification:Japan 

    Semester, Day Time or Duration:9/10

  • 2006  北九州市立大学国際環境工学部  Classification:Part-time lecturer  Domestic/International Classification:Japan 

    Semester, Day Time or Duration:火曜日4限

Other educational activity and Special note

  • 2022  Class Teacher  学部

  • 2021  Class Teacher  学部

  • 2015  Coaching of Students' Association  工学部3年生への九重研修実施

     詳細を見る

    引率

Social Activities

  • オープンキャンパス(高校生向けの研究紹介)

    九州大学  学内  2016.8

     More details

    Audience:General, Scientific, Company, Civic organization, Governmental agency

    Type:Other

  • オープンキャンパス(高校生向けの研究紹介)

    九州大学  学内  2014.8

     More details

    Audience:General, Scientific, Company, Civic organization, Governmental agency

    Type:Other

  • オープンキャンパス(高校生向けの研究紹介)

    九州大学  学内  2012.8

     More details

    Audience:General, Scientific, Company, Civic organization, Governmental agency

    Type:Other

  • オープンキャンパス(高校生向けの研究紹介)

    九州大学  学内  2011.8

     More details

    Audience:General, Scientific, Company, Civic organization, Governmental agency

    Type:Other

  • オープンキャンパス

    九州大学  学内  2011.8

     More details

    Audience:General, Scientific, Company, Civic organization, Governmental agency

    Type:Other

  • 九州大学オープンキャンパスに協力

    2011.8

     More details

    Audience:Infants, Schoolchildren, Junior students, High school students

    Type:Seminar, workshop

  • オープンキャンパス(高校生向けの研究紹介)

    九州大学  学内  2010.8

     More details

    Audience:General, Scientific, Company, Civic organization, Governmental agency

    Type:Other

  • 九州大学オープンキャンパスに協力

    2010.8

     More details

    Audience:Infants, Schoolchildren, Junior students, High school students

    Type:Seminar, workshop

  • オープンキャンパス(高校生向けの研究紹介)

    九州大学  学内  2009.8

     More details

    Audience:General, Scientific, Company, Civic organization, Governmental agency

    Type:Other

  • 九州大学オープンキャンパスに協力

    2009.8

     More details

    Audience:Infants, Schoolchildren, Junior students, High school students

    Type:Seminar, workshop

  • オープンキャンパス(高校生向けの研究紹介)

    九州大学  学内  2008.8

     More details

    Audience:General, Scientific, Company, Civic organization, Governmental agency

    Type:Other

  • 九州大学オープンキャンパスに協力

    2008.8

     More details

    Audience:Infants, Schoolchildren, Junior students, High school students

    Type:Seminar, workshop

  • オープンキャンパス(高校生向けの研究紹介)

    九州大学  学内  2007.8

     More details

    Audience:General, Scientific, Company, Civic organization, Governmental agency

    Type:Other

  • オープンキャンパス(高校生向けの研究紹介)

    九州大学  学内  2006.8

     More details

    Audience:General, Scientific, Company, Civic organization, Governmental agency

    Type:Other

  • オープンキャンパス(高校生向けの研究紹介)

    九州大学  学内  2005.8

     More details

    Audience:General, Scientific, Company, Civic organization, Governmental agency

    Type:Other

▼display all

Acceptance of Foreign Researchers, etc.

  • Acceptance period: 2015.2 - 2015.12   (Period):1 month or more

    Nationality:India

    Business entity:Japan Society for the Promotion of Science

  • Acceptance period: 2013.2 - 2014.4   (Period):1 month or more

    Nationality:India

    Business entity:Japan Society for the Promotion of Science

  • Acceptance period: 2011.7 - 2011.12   (Period):1 month or more

    Nationality:Poland

    Business entity:On-campus funds

  • JSPS

    Acceptance period: 2010.12 - 2012.11   (Period):1 month or more

    Nationality:China

    Business entity:Japan Society for the Promotion of Science

  • 北京師範大学

    Acceptance period: 2010.7 - 2010.9   (Period):1 month or more

    Nationality:China

    Business entity:On-campus funds

  • ルイビル大学

    Acceptance period: 2009.5 - 2009.11   (Period):1 month or more

    Nationality:United States

    Business entity:On-campus funds

  • 南京大学

    Acceptance period: 2008.2 - 2011.5   (Period):1 month or more

    Nationality:China

    Business entity:On-campus funds

  • Acceptance period: 2007.9 - 2009.8   (Period):1 month or more

    Nationality:Hungary

    Business entity:Japan Society for the Promotion of Science

  • Acceptance period: 2006.8 - 2006.12   (Period):1 month or more

    Nationality:Bulgaria

  • ルイビル大学

    Acceptance period: 2005.8 - 2006.10   (Period):1 month or more

    Nationality:United States

    Business entity:On-campus funds

  • Acceptance period: 2005.6 - Present   (Period):1 month or more

    Nationality:Korea, Republic of

    Business entity:Government agency

  • ライプチヒ大学

    Acceptance period: 2004.9   (Period):Less than 2 weeks

    Nationality:Bulgaria

  • Acceptance period: 2004.7 - Present   (Period):1 month or more

    Nationality:France

    Business entity:Science and Technology Agency

  • ロシアアカデミー化学物理問題研究所

    Acceptance period: 2002.7 - 2002.10   (Period):1 month or more

    Nationality:Russian Federation

    Business entity:Other

▼display all

Travel Abroad

  • 2010.12

    Staying countory name 1:United States   Staying institution name 1:ハワイ ホノルル(PACIFICHEM 2010)

  • 2007.8

    Staying countory name 1:Austria   Staying institution name 1:ウィーン大学

  • 2005.12

    Staying countory name 1:United States   Staying institution name 1:ハワイ ホノルル(PACIFICHEM 2005)

  • 2003.8

    Staying countory name 1:Australia   Staying institution name 1:ケアンズ・コンベンションセンター