Kyushu University Academic Staff Educational and Research Activities Database
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Ken Sakai Last modified date:2019.05.14

Professor / Inorganic and Analytical Chemistry
Department of Chemistry
Faculty of Sciences

Graduate School
Undergraduate School
Other Organization

Academic Degree
Doctor of Science
Field of Specialization
Coordination Chemistry, Photochemistry, Catalysis
Outline Activities
Extensive efforts have been made thus far to develop some catalytically active multinuclar metal complexes in our group. In this context, multinuclar coordination compounds involved in the active centers of the so-called metalloenzymes must be viewed as related to many of our research projects. Apart from the relatively abundant transition metals often found in the active centers of the enzyms, we have been focusing the studies on complexes with heavier or precious metals, such as Pt, Rh, and Ru. Our recent studies involve the following topics:
●Syntheses of multinuclear metal complexes with unusual electronic structures, such as strong metal-metal interactions leading to unusual/amzing reactivities.
●Development of Photosynthetic molecular devices which generate molecular hydrogen from water upon irradiation of visible light, which may be replaced with soloar light.
●Studies on the solution properties of metal complexes, which give better understanding to the reacction mechanisms of them in their catalysis.
●Syntheses, X-ray structure analysis, and physical properties of one-dimensional platinum chain complexes, where the anisotropic properties, nonlinear optical properties, metallic conduction properties, solid-satate emission properties, sensor properties (such as vapochromic behaviors upon exposure to a certain solvent gas) are focused.
●Development of molecular sensor by use of metal center as the recognition site for the sensing.
For instance, we are now interested in the development of hydrogen-sensing metal complexes.

Here students learn how to synthesize the coordination compounds including those of the ligands to be used. They also have a variety of chances to learn how to characterize, how to measure, how to calculate, how to evaluate, and so on. A large variety of analytical techniques must be used to perform the research on coordination chemistry. Thus, we think we are analytical chemists at the same time.
Research Interests
  • Development of Multinuclear Metal Complexes Applicable to the Electrode Catalysts for Fuel Cells
    keyword : Fuel Cells
  • Syntheses and Physical Properties of One-Dimensional Platinum Chain Complexes Consisting of Dinuclear Fragments Having Unusual Electronic Structures
    keyword : One-Dimensional Platinum Chain Complexes
  • Syntheses, Structures and Cytotoxicity Effects of New Pt(II)-Based Anticancer Drugs
    keyword : Anticancer Drugs, Pt(II)
  • Syntheses, Characterization, and Photocatalytic Activities of New Single-Molecule Photo-Hydrogen-Evolving Molecular Devices
    keyword : Photo-Hydrogen-Evolving Molecular Devices
  • Studies of New Homogeneous Catalysts based on Coordination Compounds towards the Water Cleavage into Molecular Hydrogen and Oxygen
    keyword : the Water Cleavage into Molecular Hydrogen and Oxygen
Current and Past Project
  • Studies on the reaction mechanism and the structure-activity relationship in the single-molecule photo-hydrogen-evolving molecular devices consisting of ruthenium and platinum centers
Academic Activities
1. Masaki Yoshida, Shigeyuki Masaoka and Ken Sakai, Oxygen Evolution from Water Catalyzed by Mononuclear Ruthenium Complexes with a Triazamacrocyclic Ligand in a Facial Fashion, Chem. Lett., 2009, 38, 702-703, 2009.07.
2. Reiko Okazaki, Shigeyuki Masaoka and Ken Sakai, Photo-Hydrogen-Evolving Activity of Chloro(terpyridine)platinum(II): a Single-Component Molecular Photocatalyst, Dalton Trans., 2009, 6127-6133, 2009.06.
3. Kosei Yamauchi, Shigeyuki Masaoka and Ken Sakai, Evidence for the Pt(II)-Based Molecular Catalysis in Thermal Reduction of Water into Molecular Hydrogen, J. Am. Chem. Soc., 2009, 131, 8404-8406, 2009.06.
4. T. Yamaguchi, S. Masaoka and K. Sakai, Hydrogen Production from Water Catalyzed by an Air-stable Di-iron Complex with a Bio-relevant Fe2(μ-S)2 Core, Chem. Lett., 2009, 38, 434-435, 2009.05.
5. S. Masaoka and K. Sakai, Clear Evidence Showing the Robustness of a Highly Active Oxygen-Evolving Mononuclear Ruthenium Complex with an Aqua Ligand, Chem. Lett., 38, 182-3, 2009.02.
6. M. J. Katz, K. Sakai and D. B. Leznoff, The use of aurophilic and other metal-metal interactions as crystal engineering design elements to increase structural dimensionality, Chem. Soc. Rev., 2008, 37(9), 1884-95., 2008.07.
7. Ken Sakai and Hironobu Ozawa, Homogeneous catalysis of platinum(II) complexes in photochemical hydrogen production from water, Coordination Chemistry Reviews, 251, 2753-2766, 2007.11.
8. Hironobu Ozawa and Ken Sakai, An Effect of Structural Modification in the Photo-hydrogen-evoluting RuIIPtII Dimers, Chemistry Letters, 36, 920-921, 2007.07.
9. Hironobu Ozawa, Yuki Yokoyama, Masa-aki Haga, and Ken Sakai, Syntheses, Characterization, and Photo-Hydrogen-Evolving Properties of Tris(2,2´-bipyridine)ruthenium(II) Derivatives Tethered to a cis-Pt(II)Cl2 Unit: Insights into the Structure-Activity Relationship, Dalton Trans., 12, 1197-1206, 2007.05.
10. Hironobu Ozawa, Masa-aki Haga, Ken Sakai, A Photo-Hydrogen-Evolving Molecular Device Driving Visible-Light-Induced EDTA-Reduction of Water into Molecular Hydrogen, J.Am.Chem.Soc., 4926-4927, 2006.04.
11. Ken Sakai, Hironobu Ozawa, Hajime Yamada, Taro Tsubomura, Mariko Hara, Akon Higuchi, Masa-aki Haga, A Tris(2,2'-bipyridine)ruthenium(II)Derivative Tetherred to a cis-PtCl2(amine)2moiety:Syntheses, Spectroscopic properties, and Visible-Light-Induced Scission of DNA, Dalton Trans., 3300-3305, 2006.04.
Works, Software and Database
1. KenX Graphical User Interface for Shelxl97 Structure Refinement..
1. 酒井 健, Molecular Catalysts and Photocatalysts for Solar Energy Conversion and Storage, 2nd Kyushu-Mainz Joint Chemistry Symposium, 2019.01.
2. Ken Sakai, Molecular Catalysts and Photocatalysts towards Artificial Photosynthesis, 東京大学理学部化学教室雑誌会セミナー(Department Seminer), 2018.12, In order to achieve practically useful artificial photosynthetic devices, we still need to gain deeper knowledge and skills in handling the basic chemical reactions catalyzed or photocatalyzed by transition metal based molecular systems. Our studies involve new materials synthesis, structure analysis, reaction kinetics, electrocatalysis, photocatalysis, DFT calculations, and so on. The presentation will focus on our recent advancements in clarifying the mechanism of some important energy-related molecular catalysis, such as hydrogen evolution, oxygen evolution, and even carbon dioxide reduction. The development of hybrid molecular devices consisting of multiple molecular components will also be discussed..
3. Ken Sakai, Coordination Chemistry focused on Photochemical Water Splitting Molecular Devices, 43rd International Conference on Coordination Chemistry(ICCC2018), 2018.07.
4. Ken Sakai, Water Oxidation and CO2 Reduction Catalyzed by Co-, Cu- and Ru-Centered Catalysts including Cobalt Porphyrins, Tenth International Conferernce on Porphyrins and Phthalocyanines(ICPP-10), 2018.07, [URL], Please refer to the attached sheet..
5. Ken Sakai, 「Catalytic Hydrogen Evolution Reactions Coupled with Proton-Coupled Electron Transfer Processes」, 3rd Interntational Conference on Proton Coulpled Electron Transfer (PCET2018), 2018.06, [URL], Please refer to the attached sheet..
6. Ken Sakai, Hybrid Molecular Catalysts and Photocatalysts for Solar Water Splitting
, 3rd Japan - UK Joint Symposium on Coordination Chemistry, 2018.04, [URL], The chemistry of water oxidation and reduction has been extensively studied from many
viewpoints due to their significant relevance to solve the problems arising from the global
warming and the shortage of fossil fuels. For both processes, proton-coupled electron
transfer (PCET) processes have been considered to play the central role in drastically
lowering the activation barriers for the relevant elementally steps. In the past decades, our
group has paid specific interest in clarifying the mechanisms of transition-metal-based
molecular catalysis for both processes [1-6]. In this presentation, some PCET processes that
govern the rate of catalytic water reduction to evolve dihydrogen from water are discussed.
The figure shown below illustrates that transition-metal-catalyzed water reduction can be
roughly considered to undergo through three different types of PCET-based ratedetermining
steps. The first metal-centered model is the case where the anti-bonding orbital
in the square planar complex like a Pt(II) system forms a hydridoplatinum(III) intermediate
[1,2,5]. This path will was also shown to undergo via formation of a diplatinum(II,III)
interemediate due to its favorable stabilization via the Pt-Pt bond formation. An exceptional
case is a Co NHC catalyst, for which metal-centered PCET occurs upon reduction of Co(II)
leading to protonation at a Co(I) d8
system [4], implying that the dz2 filled orbital
provides basicity strong enough to promote protonation at the metal center. Our recent
studies also demonstrated some unique hydride forming paths in which ligand-based
reductions coupled with protonation at the ligand geometries can lead to metal hydride
intermediate species required to catalyze hydrogen evolution from water [5,6].
1. Sakai, K.; Ozawa, H., Coord. Chem. Rev., 2007, 251, 2753.
2. Ogawa, M. Ajayakumar, G.; Masaoka, S.; Kraatz, H.-B.; Sakai, K., Chem. Eur. J., 2011,
17, 1148.
3. Kimoto, A.; Yamauchi, K.; Yoshida, M.; Masaoka, S.; Sakai, K., Chem. Commun., 2012,
48, 239.
4. Kawano, K.; Yamauchi, K.; Sakai, K., Chem. Commun., 2014, 50, 9872.
5. Yamauchi, K.; Sakai, K., Dalton Trans., 2015, 44, 8685.
6. Koshiba, K.; Yamauchi, K.; Sakai, K., Angew. Chem. Int. Ed., 2017, 56, 424.
7. Ken Sakai, Molecular Design and Control of Transition Metal Complexes and Their Hybrids for Photocatalytic Water Oxidation and Reduction, The 2018 Gordon Research Conference, 2018.01.
8. Ken Sakai, Molecular Catalysts and Photocatalysts towards Solar Energy Conversion and Storage, 11th Japan-China Joint Symposium on Metal Cluster Compounds, 2017.10.
9. Ken Sakai, Molecular Catalysts and Photocatalysts for Water Oxidation and Reduction, The 2nd Japan-US Bilateral Meeting on Coordination Chemistry, 2017.09.
10. Ken Sakai, Molecular Catalysts and Photocatalysts for Water Oxidation and Reduction, APCC2017, 2017.07.
11. Ken Sakai, Molecular Photocatalysts for Solar Water Splitting, ISPPCC2017, 2017.07.
12. Ken Sakai, Single-Molecular Hybrid Photocatalysts towards Solar Water Splitting Devices, 2017NAGC/ CTMNM Workshp, 2017.05.
13. 酒井 健, Hydrogen Production from Water Photocatalyzed by
Platinum-based Hybrid Molecular Systems, 9th Singapore International Chemistry Conference(SICC9), 2016.12.
14. 酒井 健, Hybrid Molecular Photocatalysts for Hydrogen Generation from Water, 9th Asian and Oceanian Photochemistry Conference(APC2016), 2016.12.
15. 酒井 健, Molecular Catalysts and Photocatalysts for Solar Water Splitting Reactions, Dublin City University, Trinity College Dublin, University of Cork, University of Limerick, NUI Galway, 2016.11.
16. 酒井 健, Molecular catalysts and photocatalysts towards solar water splitting reactions, Inorganic Chemistry Symposium, 2016.10.
17. 酒井 健, Hybrid Molecular Photocatalysts for Hydrogen Generation from Water, 5th International Symposium on Solar Fuels and Solar Cells (5th SFSC), 2016.10.
18. 酒井 健, Hybrid Molecular Systems for Photocatalytic Water Oxidation and Reduction, 42nd edition of the International Conference on Coordination Chemistry (ICCC2016), 2016.07.
19. 酒井 健, Molecular Catalysts and Photocatalysts for Water Splitting Reactions, Japan-Ireland joint seminar "Design and Characterization of Advanced Materials", 2016.06.
20. 酒井 健, Hybrid Molecular Photocatalysts for Hydrogen Generation from Water, UK-Japan Solar Driven Fuel Synthesis Workshop, 2016.06.
21. 酒井 健, Hybrid Molecular Catalysts towards Solar Driven Water Splitting Reactions, 2nd International Symposium on Chemical Energy Conversion Processes (ISCECP-2), 2016.05.
22. 酒井 健, Photocatalytic Water Splitting with Hybrid Molecular Systems, 26th IUPAC International Symposium on Photochemistry, 2016.04.
23. 酒井 健, Hybrid and Non-hybrid Molecular Catalysts for Solar-driven Water Splitting Reactions, City University of Hong Kong, 2016.03.
24. 酒井 健, Molecular Catalysts for Photochemical and Electrochemical Water Oxidation and Reduction, Sun Yat-Sen University, 2016.03.
25. 酒井 健, Molecular Photocatalysts and Electrocatalysts Towards Solar-driven Water Splitting, Institute of Chemical Research of Catalonia (ICIQ), 2016.03.
26. 酒井 健, Improving Robustness and TOF of Cobalt Porphyrin Water Oxidation Catalysts, 2nd Molecules and Materials for Artificial Photosynthesis Conference, 2016.02.
27. 酒井 健, Photo-driven charge storage coupled with catalytic water reduction to hydrogen, Pacifichem2015, 2015.12.
28. 酒井 健, Molecular Catalysts for Ni,Co,Rh,Pt-based H2 Evolution and Ru,Co-based O2 Evolution, Pacifichem2015, 2015.12.
29. 酒井 健, Molecular Catalysts for Solar-driven Water Splitting Reactions, 25th Annual Meeting of MRS-J (2015), 2015.12.
30. 酒井 健, Hybrid Molecular Photocatalysts Driving H2 Evolution from Water, 10th China-Japan Joint Symposium on Metal Cluster Compounds(CJSMCC-2015), 2015.10.
31. 酒井 健, Molecular Catalysis for Water Oxidation and Reduction, 2nd Japan-Germany Joint Symposium on Coordination Chemistry (JGJSCC2), 2015.09.
32. 酒井 健, Co-based molecular water oxidation catalysts, 250th ACS National Meeting & Exposition, 2015.08.
33. 酒井 健, Hybrid Molecular Catalysts for Solar-driven Water Splitting, 5th Asian Conference on Coordination Chemistry (ACCC5), 2015.07.
34. 酒井 健, Platinum-based Molecular Photocatalysts Driving Hydrogen Evolution from Water, University of Calgary, 2015.06.
35. 酒井 健, Molecular Catalysts for Photochemical Water Oxidation and Reduction, University of Montreal, 2015.06.
36. 酒井 健, Multifunctional Molecular Devices Enabling Photocatalytic Hydrogen Evolution from Water, 98th Canadian Chemistry Conference and Exhibition(CSC2015) , 2015.06.
37. 酒井 健, Molecular Catalysts and Devices for Artificial Photosynthesis, MANA国際シンポジウム2015, 2015.03.
38. 酒井 健, Molecular Devices for Photodriven Water-Splitting Reactions, 13th Eurasia Conference on Chemical Science, 2014.12.
39. 酒井 健, Multifunctional molecular devices for photoinduced hydrogen evolution from water, ICARP2014, 2014.11.
40. 酒井 健, Light-Driven Water Splitting to Dioxygen and Dihydrogen Photocatalyzed by Transition Metal Complexes, International Symposium on Green/Life Innovation, 2014.09.
41. 酒井 健, Molecular Photocatalysis For Water Splitting Reactions, International Conference on Coordination Chemistry (ICCC-41), 2014.07.
42. 酒井 健, Transition metal complexes for water splitting reactions, the 97th Canadian Chemistry Conference and Exhibition, 2014.06.
43. 酒井 健, Molecular Catalysts and Devices Driving Photoinduced Water Splitting Reactions, the 97th Canadian Chemistry Conference and Exhibition, 2014.06.
44. 酒井 健, Artificial Photosynthesis based on Molecular Photocatalysis of Water Splitting to Dihydrogen and Dioxygen, Nanomaterials for Alternative Energy Applications, 2014.05.