| 1. |
Keita Kuge, Kosei Yamauchi and Ken Sakai, Theoretical study on the mechanism of the hydrogen evolution reaction catalyzed by platinum subnanoclusters, Dalton Transactions, 10.1039/D2DT02645G, 52, 583-597, 2022.11. |
| 2. |
Yuto Sakaguchi, Arnau Call, Kosei Yamauchi, Ken Sakai, Catalysis of CO2 reduction by diazapyridinophane complexes of Fe, Co, and Ni: CO2 binding triggered by combined frontier MO associations involving a SOMO, Dalton Transactions, 10.1039/d1dt01877a, 2021.08, The Fe- and Co-based molecular catalysts are found to utilize multiple sets of frontier MO associations at the CO2 binding by including one of the SOMOs in a high-spin Fe(i) and Co(i) center, respectively, accelerating these oxidative addition steps.. |
| 3. |
Xian Zhang, Kosei Yamauchi, Ken Sakai, Earth-Abundant Photocatalytic CO2 Reduction by Multielectron Chargeable Cobalt Porphyrin Catalysts: High CO/H2 Selectivity in Water Based on Phase Mismatch in Frontier MO Association, ACS Catalysis, 10.1021/acscatal.1c02475, 11, 16, 10436-10449, 2021.08. |
| 4. |
Koichi Yatsuzuka, Kosei Yamauchi, Ken Sakai, Redox tuning in Pt(bpy)-viologen catalyst-acceptor dyads enabling photocatalytic hydrogen evolution from water, Chemical Communications, 10.1039/D1CC00903F, 57, 42, 5183-5186, 2021.05. |
| 5. |
Koichi Yatsuzuka, Kosei Yamauchi, Ken Kawano, Hironobu Ozawa, Ken Sakai, Improving the overall performance of photochemical H2evolution catalyzed by the Co-NHC complex via the redox tuning of electron relays, Sustainable Energy and Fuels, 10.1039/d0se01597k, 5, 3, 740-749, 2021.02, © The Royal Society of Chemistry 2021. The catalytic performance of a photochemical H2evolution system made up of EDTA (ethylenediaminetetraacetic acid disodium salt), [Ru(bpy)3]2+(bpy = 2,2′-bipyridine) and a macrocyclicN-heterocyclic carbene cobalt (Co-NHC-1) catalyst has been examined at pH 5.0 (E(2H+/H2) = −0.54 Vvs.SCE) by using six electron relays (ERs) having different first reduction potentials (Ered) in the range −0.69 |
| 6. |
Hoda A. El-Ghamry, Kosei Yamauchi, Ken Sakai, Thoraya A. Farghaly, Unexpected structure of enaminone Pd(II) complex in comparison with Cu(II) complex: Synthesis, characterization, DNA binding and antitumor activity, Inorganica Chimica Acta, 10.1016/j.ica.2020.120117, 120117-120117, 2020.11. |
| 7. |
Tomohiko Hamaguchi, Keisuke Kai, Isao Ando, Ken Kawano, Kosei Yamauchi, Ken Sakai, A dinuclear nickel catalyst based on metal–metal cooperation for electrochemical hydrogen production, Inorganica Chimica Acta, 10.1016/j.ica.2020.119498, 505, 2020.05, In the quest for efficient metal catalysts for hydrogen production, a new dinuclear nickel complex of formula [{(μ-2-thiazolethiolate)Ni(1,3-bis(diphenylphosphino)propane)}2](BF4)2 (2) has been synthesized. Complex 2 shows electrochemical catalytic behavior for hydrogen production with a overpotential of 0.26 V, a current efficiency of 59%, and a turnover number of 6.4. The lack of catalytic behavior of a related mononuclear complex under the same conditions suggests that the cooperation between the two Ni centers plays a pivotal role in the catalytic behavior.. |
| 8. |
Xian Zhang, Mihaela Cibian, Arnau Call, Kosei Yamauchi, Ken Sakai, Photochemical CO2 Reduction Driven by Water-Soluble Copper(I) Photosensitizer with the Catalysis Accelerated by Multi-Electron Chargeable Cobalt Porphyrin, ACS Catalysis, 10.1021/acscatal.9b04023, 9, 12, 11263-11273, 2019.12, Without using precious elements, a highly efficient and selective molecular-based photocatalytic system for CO2-to-CO conversion in fully aqueous media has been developed. Our copper(I)-based water-soluble photosensitizer (CuPS) preserves its highly luminescent and long-lived excited state even in aqueous media. The CuPS-driven CO2 reduction catalyzed by a water-soluble cobalt porphyrin possessing four N-methylpyridinium acceptors at the meso positions (CoTMPyP) achieves the highest catalytic activity among those reported for aqueous systems: TONCO = 2680 and TOFCO max = 1600-2600 h-1 with SelCO2 = 77-90% (selectivity for CO vs H2). The observed photocatalytic enhancement is discussed in terms of the 6-electron chargeable character of CoTMPyP, permitting its rapid release of CO via reduction of CoII to CoI by intramolecular electron transfer from the reducing equivalent stored at one of the acceptors.. |
| 9. |
Jia-Wei Wang, Kosei Yamauchi, Hai-Hua Huang, Jia-Kai Sun, Zhi-Mei Luo, Di-Chang Zhong, Tong-Bu Lu, Ken Sakai, A Molecular Cobalt Hydrogen Evolution Catalyst Showing High Activity and Outstanding Tolerance to CO and O₂, Angewandte Chemie - International Edition, 2019.06, There is a demand to develop molecular catalysts promoting hydrogen evolution reaction (HER) with a high catalytic rate together with high tolerance to various inhibitors, such as CO and O2. Here we report a cobalt catalyst possessing a penta‐dentate macrocyclic ligand (1‐Co), which exhibits a fast catalytic rate (TOF = 2210 s‐1) in aqueous pH 7.0 phosphate buffer solution, where proton transfer from dihydrogen phosphate anion (H2PO4‐) plays a key role in catalytic enhancement. It turns out an outstanding electrocatalyst exhibiting high tolerance to inhibitors, displaying over 90% retention in its activity under either CO or air atmosphere. Its high tolerance to CO is concluded to arise from the kinetically labile character of undesirable CO‐bound species due to the geometrical frustration posed by the ligand, prohibiting an ideal trigonal bipyramid to be established.. |
| 10. |
Arnau Call, Mihaela Cibian, Keiya Yamamoto, Takashi Nakazono, Kosei Yamauchi, Ken Sakai, Highly Efficient and Selective Photocatalytic CO2 Reduction to CO in Water by a Cobalt Porphyrin Molecular Catalyst, ACS Catalysis, 9, 4867-4874, 2019.04, The performance of a water-soluble cobalt porphyrin ([{meso-tetra(4-sulfonatophenyl)porphyrinato}cobalt(III)], CoTPPS) as a catalyst for the photoreduction of CO2 in fully aqueous media has been investigated under visible light irradiation using [Ru(bpy)3]2+ as a photosensitizer and ascorbate as a sacrificial electron donor. CO is selectively produced (>82%) with high efficiency (926 TONCO; TONCO = turnover number for CO). Upon optimization, selectivities of at least 91% are achieved. Efficiencies up to 4000 TONCO and 2400 h–1 TOFCO (TOFCO = turnover frequency for CO) are reached at low catalyst loadings, albeit with loss in selectivity. This work successfully demonstrates the ability of CoTPPS to perform highly efficient photoreduction of CO2 in water while retaining its high selectivity for CO formation.. |
| 11. |
Keita Koshiba, Kosei Yamauchi, Ken Sakai, Ligand-Based PCET Reduction in a Heteroleptic Ni(bpy)(dithiolene) Electrocatalyst Giving Rise to Higher Metal Basicity Required for Hydrogen Evolution, ChemElectroChem, 10.1002/celc.201900400, 6, 8, 2273-2281, 2019.04, Proton abstraction leading to the formation of a hydride species required to evolve H
2
largely relies on the basicity of d orbital of the metal responsible for this action. Here we report that a square-planar Ni
II
(bpy)(dcbdt) hydrogen evolution catalyst shows substantial acceleration in the proton abstraction rate due to the increased basicity at the filled Ni d
z
2 orbital after formation of [Ni
I
(bpy
−.
)(dcbdt)]
2−
via consecutive two one-electron reductions (bpy=2,2′-bipyridine; dcbdt=4,5-dicyanobenzene-1,2-dithiolate). The catalyst is likely to adopt the EECC′ mechanism in which the rate of the first protonation step is by far higher than that of the second step, even though an alternative path requiring another reduction (i. e., ECEC′) remains unexcluded. Our DFT calculations reveal that the first and second reductions are correlated with the electron injection into the metal-ligand anti-bonding and π*(bpy) orbitals, respectively, where the latter orbital shows non-negligible hybridization with the nickel d orbital. In addition, a homoleptic catalyst [Ni
II
(dcbdt)
2
]
2−
is shown to adopt the EC′EC mechanism with the rate-determing step being a hydride forming step, consistent with the largely delocalized nature of the injected electron over the two dcbdt ligands (π*(dcbdt) orbital). This work demonstrates the importance of raising the basicity of the metal d orbital, relevant to promote the proton-coupled electron transfer (PCET).. |
| 12. |
Keita Koshiba, Kosei Yamauchi, Ken Sakai, Consecutive ligand-based PCET processes affording a doubly reduced nickel pyrazinedithiolate which transforms into a metal hydride required to evolve H
2, Dalton Transactions, 10.1039/c8dt04497j, 48, 2, 635-640, 2019.01, Our DFT results demonstrate that hydrogen evolution from water catalyzed by a nickel pyradinedithiolate (dcpdt) molecular hydrogen evolution catalyst [Ni
II
(dcpdt)
2
]
2−
proceeds via the formation of a square-planar nickel(ii) hydride intermediate which is given by unprecedented structural transformation of a doubly reduced triply protonated species [Ni
II
(dcpdtH
2
)(dcpdtH)]
−
, afforded as a result of two consecutive ligand-based reductions of [Ni
II
(dcpdt)(dcpdtH)]
−
through proton-coupled electron transfer (PCET) pathways.. |
| 13. |
Yuto Sakaguchi, Arnau Call, Mihaela Cibian, Kosei Yamauchi, Ken Sakai, An earth-abundant system for light-driven CO2 reduction to CO using a pyridinophane iron catalyst, Chemical Communications, 10.1039/c9cc04191e, 55, 59, 8552-8555, 2019.01, Herein we report an earth-abundant photocatalytic system for CO2 reduction to CO based on an iron catalyst combined with a CuI photosensitizer. Under visible light irradiation CO is produced as the main product (TONCO = 565, TOFmaxCO = 114 h-1) with a high selectivity over H2 production (SelCO2 = 84%).. |
| 14. |
Yutaro Aimoto, Keita Koshiba, Kosei Yamauchi, Ken Sakai, A family of molecular nickel hydrogen evolution catalysts providing tunable overpotentials using ligand-centered proton-coupled electron transfer paths, Chemical Communications, 10.1039/C8CC07467D, 91, 12820-12823, 2018.10, Two new nickel dithiolate derivatives have been examined for their electrocatalytic activity for the hydrogen evolution reaction (HER) in attempts to clarify whether the overpotential for the HER can be tuned upon varying the ligand-centered reduction potential that triggers the HER by the catalysts. We demonstrate the validity of this approach to achieve desirable tunability in the overpotential for the HER.. |
| 15. |
Tomohiro Watanabe, Hajime Shibata, Makoto Ebine, Hiroshi Tsuchikawa, Nobuaki Matsumori, Michio Murata, Manabu Yoshida, Masaaki Morisawa, Shu Lin, Kosei Yamauchi, Ken Sakai, Tohru Oishi, Synthesis and complete structure determination of a sperm-activating and -attracting factor isolated from the ascidian ascidia sydneiensis, Journal of Natural Products, 10.1021/acs.jnatprod.7b01052, 81, 4, 985-997, 2018.04, For the complete structure elucidation of an endogenous sperm-activating and -attracting factor isolated from eggs of the ascidian Ascidia sydneiensis (Assydn-SAAF), its two possible diastereomers with respect to C-25 were synthesized. Starting from ergosterol, the characteristic steroid backbone was constructed by using an intramolecular pinacol coupling reaction and stereoselective reduction of a hydroxy ketone as key steps, and the side chain was introduced by Julia-Kocienski olefination. Comparison of the NMR data of the two diastereomers with those of the natural product led to the elucidation of the absolute configuration as 25S; thus the complete structure was determined and the first synthesis of Assydn-SAAF was achieved.. |
| 16. |
Yutaro Tsuji, Keiya Yamamoto, Kosei Yamauchi, Ken Sakai, Near-Infrared-Light-Driven Hydrogen Evolution from Water using a Polypyridyl Triruthenium Photosensitizer, Angewandte Chemie - International Edition, 2017.11. |
| 17. |
Shota Tanaka, Takashi Nakazono, Kosei Yamauchi, Ken Sakai, Photochemical H2 Evolution Catalyzed by Porphyrin-based Cubic Cages Singly and Doubly Encapsulating PtCl2(4,4’-dimethyl-2,2’-bipyridine), Chemistry Letters, 46, 1573, 2017.08. |
| 18. |
Keita Koshiba, Kosei Yamauchi, Ken Sakai, A Nickel Dithiolate Water Reduction Catalyst Providing Ligand-Based Proton-Coupled Electron-Transfer Pathways, Angewandte Chemie - International Edition, 10.1002/anie.201700927, 56, 15, 4247-4251, 2017.03, A nickel pyrazinedithiolate ([Ni(dcpdt)2]2−; dcpdt=5,6-dicyanopyrazine-2,3-dithiolate), bearing a NiS4 core similar to the active center of [NiFe] hydrogenase, is shown to serve as an efficient molecular catalyst for the hydrogen evolution reaction (HER). This catalyst shows effectively low overpotentials for HER (330–400 mV at pH 4–6). Moreover, the turnover number of catalysis reaches 20000 over the 24 h electrolysis with a high Faradaic efficiency, 92–100 %. The electrochemical and DFT studies reveal that diprotonated one-electron-reduced species forms at pH |
| 19. |
Keiya Yamamoto, Kyoji Kitamoto, Kosei Yamauchi, Ken Sakai, Pt(II)-Catalyzed photosynthesis for H2 evolution cycling between singly and triply reduced species, Chemical Communications, 10.1039/c5cc03558a, 51, 77, 14516-14519, 2015.08, A PtCl2(bpy) derivative tethered to two viologen (MV2+) moieties drives photochemical H2 evolution via forming a three-electron-reduced species possessing a bpy--based (or MV0-based) reducing equivalent. Such species can only form after one electron reduction of both the MV2+ sites because of rapid intramolecular electron transfer from bpy- to MV2+.. |
| 20. |
Kosei Yamauchi, Ken Sakai, A tricarboxylated PtCl(terpyridine) derivative exhibiting pH-dependent photocatalytic activity for H2 evolution from water, Dalton Transactions, 10.1039/c5dt00425j, 44, 18, 8685-8696, 2015.05, The first negatively charged PtCl(tpy) (tpy = 2,2′:6′,2′′-terpyridine) derivative, formulated as Na2[PtCl(tctpy)]·5H2O (tctpy = 2,2′:6′,2′′-terpyridine-4,4′,4′′-tricarboxylate), was prepared, characterized, and investigated in detail for its activity as a single-component photocatalyst that drives water reduction to H2 in the presence of a sacrificial electron donor (EDTA). This compound was confirmed to exist in its fully deprotonated form [PtCl(tctpy)]2- in aqueous media at pH > 4.4. Despite its dianionic character, [PtCl(tctpy)]2- was found to form a specific adduct with anionic EDTA (i.e., YH2 2- and YH3-, where YH4 is a fully protonated form of EDTA), enabling reductive quenching of the triplet metal-to-ligand charge transfer excited state within the adduct, leading to subsequent electron transfer steps correlated with Pt(ii)-catalyzed H2 evolution from water. Electrochemical studies also reveal that the compound exhibits a unique pH-dependent first reduction (i.e., tctpy-centered reduction), leading to our realization of the first example of a Pt(ii)-based molecular system that photocatalyzes the H2 evolution reaction accompanied by a ligand-based proton-coupled electron transfer (PCET) process.. |
| 21. |
Ken Kawano, Kosei Yamauchi, Ken Sakai, A cobalt-NHC complex as an improved catalyst for photochemical hydrogen evolution from water, Chemical Communications, 10.1039/c4cc03493g, 50, 69, 9872-9875, 2014.09, A macrocyclic N-heterocyclic carbene (NHC)-cobalt complex was found to act as an improved H2-evolving catalyst in a [Ru(bpy)3] 2+-sensitized photosystem using methylviologen as a redox acceptor (MV2+ + e- → MV+•, MV2+ = N,N'-dimethyl-4,4′-bipyridinium), which provides a driving force of only 150 meV for H2 evolution at pH 5.0.. |
| 22. |
Kosei Yamauchi, Homogeneous Catalysis of Nickel(II) Complexes Promoting Hydrogen Production with High Turnover Numbers, Bull. Jpn. Soc. Coord. Chem., 62, 26-28, 2013.11. |
| 23. |
Ayano Kimoto, Kosei Yamauchi, Masaki Yoshida, Shigeyuki Masaoka, Ken Sakai, Kinetics and DFT studies on water oxidation by Ce4+ catalyzed by [Ru(terpy)(bpy)(OH2)]2+, Chemical Communications, 10.1039/c1cc15109f, 48, 2, 239-241, 2012.01, The RuVO species and other intermediates in O2 evolution from water catalyzed by [Ru(terpy)(bpy)(OH2)]2+ were spectrophotometrically characterized, and the spectral components observed were identified based on the TD-DFT calculations. Moreover, important insights into the rapid paths after the RDS were given by the DFT studies.. |
| 24. |
Kosei Yamauchi, Shigeyuki Masaoka, Ken Sakai, Stability of Pt(ii)-based H2-evolving catalysts against H 2 in aqueous solution, Dalton Transactions, 10.1039/c1dt11217a, 40, 46, 12447-12449, 2011.12, To answer the question of whether Pt(ii)-based H2-evolving catalysts are stable upon exposure to H2, the behaviours of some platinum(ii) complexes in the presence of H2 (5 × 10 -4 - 1 atm) have been followed spectrophotometrically. The results reveal that some catalysts are highly stable upon exposure to H2.. |
| 25. |
Saya Tanaka, Shigeyuki Masaoka, Kosei Yamauchi, Annaka Masahiko, Ken Sakai, Photochemical and thermal hydrogen production from water catalyzed by carboxylate-bridged dirhodium(ii) complexes, Dalton Transactions, 10.1039/c0dt00741b, 39, 46, 11218-11226, 2010.12, A series of dinuclear Rh(ii) complexes, [Rh2(μ-OAc) 4(H2O)2] (HOAc = acetic acid) (1), [Rh 2(μ-gly)4(H2O)2] (Hgly = glycolic acid) (2), [Rh2(μ-CF3CO2) 4(acetone)2] (3), and [Rh2(bpy) 2(μ-OAc)2(OAc)2] (4), were found to serve as H2-evolving catalysts in a three-component system consisting of tris(2,2′-bipyridine)ruthenium(ii) (Ru(bpy)32+), methylviologen (MV2+), and ethylenediaminetetraacetic acid disodium salt (EDTA). It was also confirmed that thermal reduction of water into H 2 by MV+, in situ generated by the bulk electrolysis of MV2+, is effectively promoted by 1 as a H2-evolving catalyst. The absorption spectra of the photolysis solution during the photocatalysis were monitored up to 6 h to reveal that the formation of photochemical or thermal byproducts of MV+ is dramatically retarded in the presence of the Rh(ii)2 catalysts, for the H2 formation rather than the decomposition of MV+ becomes predominant in the presence of the Rh(ii)2 catalysts. The stability of the Rh(ii)2 dimers was confirmed by absorption spectroscopy, 1H NMR, and ESI-TOF mass spectroscopy. The results indicated that neither elimination nor replacement of the equatorial ligands take place during the photolysis, revealing that one of the axial sites of the Rh2 core is responsible for the hydrogenic activation. The quenching of Ru*(bpy)32+ by 1 was also investigated by luminescence spectroscopy. The rate of H2 evolution was found to decrease upon increasing the concentration of 1, indicating that the quenching of Ru*(bpy)32+ by the Rh(ii)2 species rather than by MV2+ becomes predominant at the higher concentrations of 1. The DFT calculations were carried out for several possible reaction paths proposed (e.g., [RhII2(μ-OAc)4(H 2O)] + H+ and [RhII2(μ-OAc) 4(H2O)] + H+ + e-). It is suggested that the initial step is a proton-coupled electron transfer (PCET) to the Rh(ii)2 dimer leading to the formation of a Rh(ii)Rh(iii)-H intermediate. The H2 evolution step is suggested to proceed either via the transfer of another set of H+ and e- to the Rh(ii)Rh(iii)-H intermediate or via the homolytic radical coupling through the interaction of two Rh(ii)Rh(iii)-H intermediates.. |
| 26. |
Kosei Yamauchi, Shigeyuki Masaoka, Ken Sakai, Evidence for Pt(II)-based molecular catalysis in the thermal reduction of water into molecular hydrogen, Journal of the American Chemical Society, 10.1021/ja902245e, 131, 24, 8404-8406, 2009.06, (Figure Presented) The one-electron-reduced form of methylviologen (MV +.), generated in situ by bulk electrolysis of methylviologen (MV2+), was for the first time reacted with various Pt(II) complexes in aqueous media without light irradiation to reveal that thermal reduction of water into molecular hydrogen is indeed highly promoted by the Pt(II)-based molecular catalysts.. |
