Updated on 2024/02/03

写真b

 
WADA Tohru
 
*Items subject to periodic update by Rikkyo University (The rest are reprinted from information registered on researchmap.)
Affiliation*
College of Science Department of Chemistry
Graduate School of Science Doctoral Program in Chemistry
Graduate School of Science Master's Program in Chemistry
Title*
Professor
Degree
博士(理学) ( 総合研究大学院大学 )
Contact information
Mail Address
Research Theme*
  • 錯体化学。エネルギー・環境問題の観点から大きな注目を集めている燃料電池や人工光合成などのエネルギー変換システムを構築する上で、欠かす事の出来ない電気化学的な酸化還元反応を触媒する遷移金属錯体の開発を行っている。精密にデザインされた錯体を合成し、平衡電位近傍での水の酸化反応や酸素還元反応をめざしている。

  • Research Interests
  • Complex Catalyst Chemistry

  • Campus Career*
    • 4 2017 - Present 
      College of Science   Department of Chemistry   Professor
    • 4 2017 - Present 
      Graduate School of Science   Master's Program in Chemistry   Professor
    • 4 2017 - Present 
      Graduate School of Science   Doctoral Program in Chemistry   Professor
    • 4 2010 - 3 2017 
      College of Science   Department of Chemistry   Associate Professor
    • 4 2010 - 3 2017 
      Graduate School of Science   Master's Program in Chemistry   Associate Professor
    • 4 2010 - 3 2017 
      Graduate School of Science   Doctoral Program in Chemistry   Associate Professor

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    Research Areas

    • Nanotechnology/Materials / Inorganic/coordination chemistry  / Artificial Photosynthesis

    • Nanotechnology/Materials / Energy chemistry  / Coordination Chemistry

    Research History

    • 4 2017 - Present 
      RIKKYO UNIVERSITY   College of Science Department of Chemistry   Professor

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    • 4 2017 - Present 
      RIKKYO UNIVERSITY   Graduate School of Science Field of Study: Chemistry   Professor

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    • 4 2017 - Present 
      RIKKYO UNIVERSITY   Graduate School of Science Field of Study: Chemistry   Professor

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    • 4 2010 - 3 2017 
      RIKKYO UNIVERSITY   College of Science Department of Chemistry   Associate Professor

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    • 4 2001 - 3 2010 
      National Institutes of Natural Sciences

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    Education

    • 4 1998 - 3 2001 
      The Graduate University for Advanced Studies   Graduate School, Division of Mathematical and Physical Science

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      Country: Japan

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    • 4 1996 - 3 1998 
      Gakushuin University   Graduate School of Natural Science   Graduate Course in Chemistry

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      Country: Japan

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    • 4 1992 - 3 1996 
      Gakushuin University   Faculty of Science   Department of Science

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      Country: Japan

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    Papers

    • Photochemical CO<sub>2</sub> Reduction to CO Catalyzed by a Doubly N-Confused Hexaphyrin Dinuclear Iron Complex

      Takashi Nakazono, Daichi Sugawara, Takashi Ito, Yusuke Yamada, Tohru Wada

      Chemistry Letters52 ( 6 ) 481 - 484   5 6 2023

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      Publishing type:Research paper (scientific journal)   Publisher:The Chemical Society of Japan  

      DOI: 10.1246/cl.230141

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    • Electrochemical hydrogen evolution reaction catalysed by a dinuclear cobalt complex with doubly N-confused hexaphyrin

      Risa Takada, Takashi Nakazono, Taiyo Nishimura, Takuya Shiga, Masayuki Nihei, Yusuke Yamada, Tohru Wada

      Sustainable Energy &amp; Fuels7 ( 15 ) 3603 - 3608   2023

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

      A dinuclear cobalt complex with a doubly N-confused hexaphyrin, Co2DNCH, showed high catalytic activity for electrochemical hydrogen reduction due to the wide π-conjugated system of DNCH.

      DOI: 10.1039/d3se00403a

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    • Proton Relay Effects on Oxygen Reduction Reaction Catalyzed by Dinuclear Cobalt Polypyridyl Complexes with OH Groups on Bipyridine Ligands

      Hiroaki Arima, Takashi Nakazono, Tohru Wada

      Bulletin of the Chemical Society of Japan95 ( 7 ) 1100 - 1110   15 7 2022

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      Publishing type:Research paper (scientific journal)   Publisher:The Chemical Society of Japan  

      DOI: 10.1246/bcsj.20220104

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    • High quantum yield photochemical water oxidation using a water-soluble cobalt phthalocyanine as a homogenous catalyst

      Takashi Nakazono, Nagisa Amino, Risa Matsuda, Daichi Sugawara, Tohru Wada

      Chemical Communications58 ( 55 ) 7674 - 7677   2022

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

      A water-soluble cobalt phthalocyanine complex with sulfonate groups (CoPcTS) serves as an effective homogenous catalyst for photochemical water oxidation using a [Ru(bpy)<sub>3</sub>]<sup>2+</sup>/S<sub>2</sub>O<sub>8</sub><sup>2−</sup> photosystem.

      DOI: 10.1039/d2cc01985j

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    • Tuning Oxygen Reduction Catalysis of Dinuclear Cobalt Polypyridyl Complexes by the Bridging Structure

      Hiroaki Arima, Misato Wada, Takashi Nakazono, Tohru Wada

      Inorganic Chemistry60 ( 13 ) 9402 - 9415   14 5 2021

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      Publishing type:Research paper (scientific journal)   Publisher:American Chemical Society (ACS)  

      DOI: 10.1021/acs.inorgchem.1c00293

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    • Photochemical Water Oxidation Using a Doubly N-Confused Hexaphyrin Dinuclear Cobalt Complex Peer-reviewed

      Takashi Nakazono, Tohru Wada

      INORGANIC CHEMISTRY60 ( 3 ) 1284 - 1288   2 2021

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      Authorship:Corresponding author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER CHEMICAL SOC  

      A doubly N-confused hexaphyrin dinuclear cobalt complex (Co2DNCH) is revealed as an efficient water oxidation catalyst, outperforming the mononuclear cobalt porphyrin with the same aryl group as those in Co2DNCH. By photoirradiation of a water/acetone-d(6) (9:1) mixture containing Co2DNCH, [Ru-II(bpy)(3)](2+), and S2O82- as the water oxidation catalyst, photosensitizer, and sacrificial electron acceptor, respectively, with visible light, O-2 was obtained as the maximum with turnover number = 1200, turnover frequency = 3.9 s(-1), and quantum yield = 0.30.

      DOI: 10.1021/acs.inorgchem.0c02602

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    • Preparation and Characterization of a mu-P2O7-mu-HPO4 Dinuclear Fe-2(III, III) Complex Peer-reviewed

      Yuji Miyazato, Kouta Imaizumi, Rikako Tanaka, Tohru Wada, Nobuyuki Matsushita

      BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN91 ( 5 ) 787 - 789   5 2018

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:CHEMICAL SOC JAPAN  

      The [{Fe(Me(3)tacn)}(2)(mu-P2O7)(mu-HPO4)]center dot 12H(2)O dinuclear Fe-2(III, III) complex was prepared. The HPO42- bridge in the complex arises from hydrolysis of the pyrophosphate bound to the Fe(III) centers in the trinuclear [{Fe(Me(3)tacn)}(3)-(P2O7)(2)](+) intermediate. Electrochemical reduction of this complex at pH < 3.2 results in dissociation of the H2PO4 bridge.

      DOI: 10.1246/bcsj.20170427

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    • Mechanism of Water Oxidation Catalyzed by a Dinuclear Ruthenium Complex Bridged by Anthraquinone Invited Peer-reviewed

      Tohru Wada, Shunsuke Nishimura, Taro Mochizuki, Tomohiro Ando, Yuji Miyazato

      CATALYSTS7 ( 2 ) 56/1 - 56/16   2 2017

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:MDPI AG  

      We synthesized 1,8-bis(2,2':6',2"-terpyrid-4'-yl)anthraquinone (btpyaq) as a new dimerizing ligand and determined its single crystal structure by X-ray analysis. The dinuclear Ruthenium complex [Ru-2(mu-Cl)(bpy)(2)(btpyaq)](BF4)(3) ([3](BF4)(3), bpy = 2,2'-bipyridine) was used as a catalyst for water oxidation to oxygen with (NH4)(2)[Ce(NO3)(6)] as the oxidant (turnover numbers = 248). The initial reaction rate of oxygen evolution was directly proportional to the concentration of the catalyst and independent of the oxidant concentration. The cyclic voltammogram of [3](BF4)(3) in water at pH 1.3 showed an irreversible catalytic current above +1.6 V (vs. SCE), with two quasi-reversible waves and one irreversible wave at E-1/2 = +0.62, +0.82 V, and E-pa = +1.13 V, respectively. UV-vis and Raman spectra of [3](BF4)(3) with controlled-potential electrolysis at +1.40 V revealed that [Ru(IV)=O O=Ru(IV)](4+) is stable under electrolysis conditions. [Ru(III), Ru(II)] species are recovered after dissociation of an oxygen molecule from the active species in the catalytic cycle. These results clearly indicate that an O-O bond is formed via [Ru(V)=O O=Ru(IV)](5+).

      DOI: 10.3390/catal7020056

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    • Synthesis and Characterization of an Ru-2(III, IV) Complex Containing Pyrophosphate Bridge Peer-reviewed

      Yuji Miyazato, Tohru Wada, Masaaki Ohba, Nobuyuki Matsushita

      CHEMISTRY LETTERS45 ( 12 ) 1388 - 1390   12 2016

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:CHEMICAL SOC JAPAN  

      We prepared a new Ru-2(III, IV) complex containing a pyrophosphate as the dinucleating component, by the reaction between the mononuclear complex [Ru(Me(3)tacn)Cl-3] and Na4P2O7 center dot 10H(2)O in aqueous solution. Cyclic voltammetric measurement for the complex [{Ru(Me(3)tacn)}(2)(mu-O)(mu-P2O7)]PF6 (1) in aqueous solution revealed the formation of two species with higher oxidation states, such as [O=Ru(IV)Ru(IV)=O] and [O=Ru(IV)Ru(V)=O](+). Furthermore, this complex showed activity for water oxidation reaction with Ce(NH4)(2)(NO3)(6) as the chemical oxidant in acidic aqueous solution.

      DOI: 10.1246/cl.160721

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    • Water Oxidation Catalyzed by a Ruthenium Complex with an Ru-C Bond Peer-reviewed

      Tohru Wada, Takahide Hiraide, Yuji Miyazato

      CHEMISTRYSELECT1 ( 12 ) 3045 - 3048   8 2016

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:WILEY-V C H VERLAG GMBH  

      We prepared a new Ru(III) complex with a covalent bond between the central Ru and C of the ligand, [RuCl(dpp)(bpy)] Cl ([1] Cl, dpp= 2,6-dipyridylphenyl, bpy= 2,2'-bipyridine), through the reaction of [(eta(6)-C6H6) RuCl(bpy)] Cl with one equivalent of 1,3-di(pyrid-2-yl) benzene. X-ray analysis of a single crystal of [1](PF6), which was prepared via the anion exchange of [1] Cl, revealed the short Ru-C bond length of [1](+). [1] Cl was easily hydrolyzed in a neutral water solution to the hydroxo complex, [Ru(OH)(dpp)(bpy)](+) ([2](+)). Cyclic voltammetry of [1]+ showed that the Ru(II)/ Ru(III) potential of [1](+) was more negative than that of the 2,2': 6', 2"-terpyridine (trpy) analogue, [RuCl(bpy)(trpy)](ClO4), by -770 mV under the same conditions. Moreover, the Ru(V)= O species, which is a key intermediate of water oxidation, was produced by electrochemical oxidation of [2](+) at an extremely negative potential (+ 0.80 V vs. saturated calomel electrode). [2](+) catalyzed water oxidation at pH 2.5 with [Ru (bpy)(3)](3+) as the oxidant. 2,6-dipyridylphenyl as a strong s-electron donor ligand negatively shifted the oxidation potential of water.

      DOI: 10.1002/slct.201600716

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    • Synthesis and Characterization of a Di-mu-oxalato Tetracopper(II) Complex with Tetranucleating Macrocyclic Ligand Peer-reviewed

      Yuji Miyazato, Eiji Asato, Masaaki Ohba, Tohru Wada

      BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN89 ( 4 ) 430 - 436   4 2016

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:CHEMICAL SOC JAPAN  

      A tetracopper(II) complex containing two oxalate anions in the metal-based host cavity, [Cu-4(L-py)(mu-ox)(2)](PF6)(2)center dot 2(2-PrOH), where ox(2-): oxalato (C2O42-), was prepared by reacting H2Lpy, a phenol-based tetranucleating macrocyclic ligand with four pyridylmethyl pendant arms, Cu(ClO4)(2)center dot 6H(2)O, and sodium oxalate (1:4:2 stoichiometry, respectively) in methanol, followed by exchange of the counteranion with excess of NH4PF6. Single-crystal X-ray diffraction of 1 revealed that two {Cu(II)Cu(II)} units, bridged by a phenolato group of L-py(2-), were connected by two oxalato anions, to construct a rectangular "{CuCu}(mu-ox)(2){CuCu}" tetranuclear framework. This rectangular framework was maintained in DMF solution. The magnetic measurement of 1 in the 2-300 K range revealed antiferromagnetic behavior. The antiferromagnetic interaction in this complex occurs between the Cu(II) centers bridged by an oxalate (J = -140 cm(-1)).

      DOI: 10.1246/bcsj.20150338

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    • Homogeneous Photocatalytic Water Oxidation with a Dinuclear Co-III-Pyridylmethylamine Complex Peer-reviewed

      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 CHEMISTRY55 ( 3 ) 1154 - 1164   2 2016

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER CHEMICAL SOC  

      A bis-hydroxo-bridged dinuclear Co-III-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 [Ru-II(bpy)(3)](2+) (bpy = 2,2'-bipyridine) as a photosensitizer affording a high quantum yield (44%) with a large turnover number (TON = 742) for O-2 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-mu-oxyl Co-III complex (2), which has been suggested by DFT calculations. Catalytic water oxidation by 1 using [Ru-III(bpy)(3)](3+) as an oxidant in a (H2O)-O-16 and (H2O)-O-18 mixture was examined to reveal an intramolecular O-O bond formation in the two-electron-oxidized bis-mu-oxyl intermediate, prior to the O-2 evolution.

      DOI: 10.1021/acs.inorgchem.5b02336

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    • Reversible Structural Changes Accompanying the Two-Electron Redox Reaction of Pt(tacn) (tacn: 1,4,7-triazacyclononane) Complexes Peer-reviewed

      Tohru Wada, Koki Enami, Ryohei Kojima, Tomoki Okada, Yuki Ishikawa, Yuji Miyazato, Ernst Horn, Yuji Mochizuki

      BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN88 ( 9 ) 1230 - 1237   9 2015

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:CHEMICAL SOC JAPAN  

      Platinum complexes with 1,4,7-triazacyclononane (tacn) as facial ligands, [(PtCl3)-Cl-Iv(tacn)](ClO4), [(PtCl)-Cl-Iv(bpy)-(tacn)](ClO4)(3) ([1](ClO4), and [2](ClO4)(3), bpy: 2,2'-bipyridine) were prepared, and their hexa-coordinated octahedral structures were determined via single-crystal X-ray analysis. In aqueous solutions containing NaCl as the electrolyte, [2](3+) exhibited a quasi-reversible two-electron redox wave at +0.22 V (vs. SCE) with a large peak separation Delta E = E-pc - E-pa = 0.28 V). In addition, controlled-potential reduction of [2](3+) at -0.30 V in aqueous solutions containing NaCl afforded [Pt-II(bpy)(tacn)](2+) ([3](2+)), which was then re-oxidized to regenerate [2](3+). X-ray analysis of [3](2+) revealed a tetra-coordinated square-planar structure in which both tacn and bpy were bound to the central Pt as bidentate ligands. The redox potential of this reaction is coupled with dissociation/association of Cl- from/to Pt in the solution. MO/DFT calculations indicate that structural changes in tacn promote the reversible two-electron redox reaction between the octahedral Pt(IV) and square planar Pt(II) complexes.

      DOI: 10.1246/bcsj.20150097

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    • Four-electron reduction of dioxygen catalysed by dinuclear cobalt complexes bridged by bis(terpyridyl)anthracene Peer-reviewed

      Tohru Wada, Hidetaka Maki, Tomoyuki Imamoto, Hirokazu Yuki, Yuji Miyazato

      CHEMICAL COMMUNICATIONS49 ( 39 ) 4394 - 4396   2013

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:ROYAL SOC CHEMISTRY  

      Dinuclear cobalt-1,10-phenanthroline (1) and 2,2'-bipyridine (2) complexes bridged by 1,8-bis(2,2':6',2 ''-terpyrid-4'-yl)anthracene (btpyan) were prepared. Both of the complexes selectively catalysed the electrochemical four-electron reduction of dioxygen to H2O without the generation of H2O2 as a two-electron reduction product.

      DOI: 10.1039/c2cc36528f

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    • Synthesis and Characterization of a Tetracopper(II) Complex Having a [Cu-4(mu(4)-O)] Framework Stabilized by the Tetranucleating Macrocyclic Ligand Peer-reviewed

      Yuji Miyazato, Eiji Asato, Masaaki Ohba, Tohru Wada

      BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN85 ( 8 ) 895 - 901   8 2012

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:CHEMICAL SOC JAPAN  

      A tetranucleating macrocyclic ligand bearing four acetate pendants, L6-, was newly yielded by a stepwise synthesis from [Zn-4(L')(AcO)(2)(OH)(2)](ClO4)(2)center dot H2O (1), which was prepared from [2 + 2] Schiff-base condensation of 2,6-diformyl-4-methylphenol and 1,2-bis(2-aminoethoxy)ethane in the presence of Zn(ClO4)(2)center dot 6H(2)O, sodium acetate, and triethylamine. A mu(4)-oxo tetracopper(II) complex [Cu-4(L)(mu(4)-O)]center dot H2O (2) was obtained from the reaction of Cu(ClO4)(2)center dot 6H(2)O and Na2H4L in methanol under basic conditions, and characterized by X-ray crystallography. Two adjacent copper centers were bridged by the phenoxo oxygen of L6- to form [Cu20.1-0Ph)] unit, two pairs of which were further linked by an oxo anion with a distorted tetrahedral geometry, finally creating a tetracopper core [(Cu-2-mu-OPh)}(2)(mu(4)-O)]. Cryomagnetic measurements of 2 in the range of 2-300 K exhibited antiferromagentic behavior. Magnetic analysis of 2 was carried out by the four spin-exchange interactions model based on the bridging mode and the Cu-(mu(4)-O)-Cu angles, J(A): Cu1/Cu4, J(B): Cu2/Cu3, J(C): Cu1/Cu2 and Cu3/Cu4, and J(D): Cu1/Cu3 and Cu2/Cu4 pairs. The estimated four magnetic exchange interactions (J(A), J(B), J(C), and J(D)) were -17, -161, -108, and -109 cm(-1), respectively.

      DOI: 10.1246/bcsj.20120084

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    • Catalytic Four-Electron Oxidation of Water by Intramolecular Coupling of the Oxo Ligands of a Bis(ruthenium-bipyridine) Complex Peer-reviewed

      Tohru Wada, Hideki Ohtsu, Koji Tanaka

      CHEMISTRY-A EUROPEAN JOURNAL18 ( 8 ) 2374 - 2381   2 2012

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:WILEY-V C H VERLAG GMBH  

      A bis(rutheniumbipyridine) complex bridged by 1,8-bis(2,2':6',2''-terpyrid-4'-yl)anthracene (btpyan), [Ru2(mu-Cl)(bpy)2(btpyan)](BF4)3 ([1](BF4)3; bpy=2,2'-bipyridine), was prepared. The cyclic voltammogram of [1](BF4)3 in water at pH 1.0 displayed two reversible [RuII,RuII]3+/[RuII,RuIII]4+ and [RuII,RuIII]4+/[RuIII,RuIII]5+ redox couples at E1/2(1)=+0.61 and E1/2(2)=+0.80 V (vs. Ag/AgCl), respectively, and an irreversible anodic peak at around E=+1.2 V followed by a strong anodic currents as a result of the oxidation of water. The controlled potential electrolysis of [1]3+ ions at E=+1.60 V in water at pH 2.6 (buffered with H3PO4/NaH2PO4) catalytically evolved dioxygen. Immediately after the electrolysis of the [1]3+ ion in H216O at E=+1.40 V, the resultant solution displayed two resonance Raman bands at $\tilde \nu $=442 and 824 cm-1. These bands shifted to $\tilde \nu $=426 and 780 cm-1, respectively, when the same electrolysis was conducted in H218O. The chemical oxidation of the [1]3+ ion by using a CeIV species in H216O and H218O also exhibited the same resonance Raman spectra. The observed isotope frequency shifts (?$\tilde \nu $=16 and 44 cm-1) fully fit the calculated ones based on the Ru?O and O?O stretching modes, respectively. The first successful identification of the metal?O?O?metal stretching band in the oxidation of water indicates that the oxygenoxygen bond at the stage prior to the evolution of O2 is formed through the intramolecular coupling of two Ruoxo groups derived from the [1]3+ ion.

      DOI: 10.1002/chem.201102236

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    • Substituents dependent capability of bis(ruthenium-dioxolene-terpyridine) complexes toward water oxidation Invited Peer-reviewed

      Tohru Wada, James T. Muckerman, Etsuko Fujita, Koji Tanaka

      DALTON TRANSACTIONS40 ( 10 ) 2225 - 2233   2011

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:ROYAL SOC CHEMISTRY  

      The bridging ligand, 1,8-bis(2,2':6',2 ''-terpyrid-4'-yl)anthracene (btpyan) was synthesized by the Miyaura-Suzuki cross coupling reaction of anthracenyl-1,8-diboronic acid and 4'-triflyl-2,2': 6'-2 ''-terpyridine in the presence of Pd(PPh3)(4) (5 mol%) with 68% in yield. Three ruthenium-dioxolene dimers, [Ru-2(OH)(2)(dioxolene)(2)(btpyan)](0) (dioxolene = 3,6-di-tert-butyl-1,2-benzosemiquinone ([1](0)), 3,5-dichloro-1,2-benzosemiquinone ([2](0)) and 4-nitro-1,2-benzosemiquinone ([3](0))) were prepared by the reaction of [Ru2Cl6(btpyan)](0) with the corresponding catechol. The electronic structure of [1](0) is approximated by [Ru-2(II)(OH)(2)(sq)(2)(btpyan)](0) (sq = semiquinonato). On the other hand, the electronic states of [2](0) and [3](0) are close to [Ru-2(III)(OH)(2) (cat)(2)(btpyan)](0) (cat = catecholato), indicating that a dioxolene having electron-withdrawing groups stabilizes [Ru-2(III)(OH)(2)(cat)(2)(btpyan)](0) rather than [Ru-2(II)(OH)(2)(sq)(2)(btpyan)](0) as resonance isomers. No sign was found of deprotonation of the hydroxo groups of [1](0), whereas [2](0) and [3](0) showed an acid-base equilibrium in treatments with t-BuOLi followed by HClO4. Furthermore, controlled potential electrolysis of [1](0) deposited on an ITO (indium-tin oxide) electrode catalyzed the four-electron oxidation of H2O to evolve O-2 at potentials more positive than +1.6 V (vs. SCE) at pH 4.0. On the other hand, the electrolysis of [2](0) and [3](0) deposited on ITO electrodes did not show catalytic activity for water oxidation under similar conditions. Such a difference in the reactivity among [1](0), [2](0) and [3](0) is ascribed to the shift of the resonance equilibrium between [Ru-2(II)(OH)(2)(sq)(2)(btpyan)](0) and [Ru-2(III)(OH)(2)(cat)(2)(btpyan)](0).

      DOI: 10.1039/c0dt00977f

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    • A new type of electrochemical oxidation of alcohols mediated with a ruthenium-dioxolene-amine complex in neutral water Peer-reviewed

      Hironobu Ozawa, Takami Hino, Hideki Ohtsu, Tohru Wada, Koji Tanaka

      INORGANICA CHIMICA ACTA366 ( 1 ) 298 - 302   1 2011

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:ELSEVIER SCIENCE SA  

      Electrochemical oxidation of [Ru-II(terpy)(sq)(NH3)](+) in neutral water (pH 8.0) at +0.8 V (versus SCE) generated [Ru-II(terpy)(q)(NH2 center dot)](2+) and/or [Ru-III(terpy)(sq)(NH2 center dot)](2+) (terpy = 2,2':6',2 ''-terpyridine, sq = 3,5-di-tert-butyl-1,2-semiquinonate, q = 3,5-di-tert-butyl-1,2-benzoquinone), which played roles in hydrogen abstraction and one-electron acceptor in the catalytic oxidation of methanol, ethanol, and 2-propanol affording formaldehyde, acetoaldehyde, and acetone, respectively, under the electrolysis conditions. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.

      DOI: 10.1016/j.ica.2010.11.013

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    • Redox Behavior of Ruthenium(Bipyridine)(Terpyridine)(Carbonyl) Complex-modified Carbon Electrode and Reactivity toward Electrochemical Reduction of CO2 Peer-reviewed

      Yuhei Tsukahara, Tohru Wada, Koji Tanaka

      CHEMISTRY LETTERS39 ( 11 ) 1134 - 1135   11 2010

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:CHEMICAL SOC JAPAN  

      Electrochemical reduction of a diazonium complex [Ru-(bpy)(trpy-ph-N-2(+))(CO)](PF6)(3) ([1](PF6)(3)) (bPY = dine, trpy-ph-N-2(+) = 4-(2,2' 6',2"-terpyncline-4'-yl)benzenedi-azonium) using a GC electrode forms multdayer films of the complexes on the electrode surface, on which the reduced form of the complex showed strong affinity toward CO2

      DOI: 10.1246/cl.2010.1134

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    • Formation and Structure of an (Iminium ion)ruthenium Complex and Reaction of the Iminium Ion Moiety with Alcohols Peer-reviewed

      Sohei Fukui, Noriyuki Suzuki, Tohru Wada, Koji Tanaka, Hirotaka Nagao

      ORGANOMETALLICS29 ( 7 ) 1534 - 1536   4 2010

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER CHEMICAL SOC  

      The (iminium ion)ruthenium(II) complex mer(Cl, Cl,Cl)-[RuCl3{eta(2)-NCHCH(2)py(C(2)H(4)py)C2H5}] was synthesized via a C-H activation of the bridging ethyl group of an ethylbis(2-pyridylethyl)amine ligand and characterized by X-ray structural analysis. Oxidations of alcohols by the (iminium ion)ruthenium(11) complex occurred with generation of mer-[(RuCl3)-Cl-III(ebpea)].

      DOI: 10.1021/om100161r

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    • Photoinduced four- and six-electron reduction of mononuclear ruthenium complexes having NAD(+) analogous ligands Peer-reviewed

      Takashi Fukushima, Tohru Wada, Hideki Ohtsu, Koji Tanaka

      DALTON TRANSACTIONS39 ( 48 ) 11526 - 11534   2010

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:ROYAL SOC CHEMISTRY  

      The ruthenium complexes [Ru(bpy)(pbn)(2)](PF6)(2) ([2](2+); bpy = 2,2'-bipyridine, pbn = 2-(2-pyridyl)benzo[b]-1,5-naphthyridine) and [Ru(pbn)(3)](PF6)(2) ([3](2+)) were synthesized. Photoirradiation (lambda > 420 nm) of [2](2+) and [3](2+) in CH3CN/triethanolamine (TEOA) brought about proton coupled four-and six-electron reduction of the complexes to produce [Ru(bpy)(pbnH(2))(2)](PF6)(2) ([2.H-4](2+); pbnH(2) = 5,10-dihydro-2-(2-pyridyl)benzo[b]-1,5-naphthyridine) and [Ru(pbnH(2))(3)](PF6)(2) ([3.H-6](2+)), respectively. The photoexcited [Ru-III(bpy)(pbn(center dot-))(pbnH(2))](2+) intermediate is quenched by intermolecular electron transfer from TEOA to Ru-III, while intramolecular transfer from pbnH(2) to Ru-III is negligible. As a result, novel photochemical four-and six-electron reduction of [2](2+) and [3](2+) is achieved through repetition of the two-electron reduction of the Ru-pbn group. The high efficiency photochemical two-, four- and six-electron reductions of [Ru(bpy)(2)(pbn)](2+) ([1](2+)), [2](2+) and [3](2+), respectively, by taking advantage of proton coupled two electron reduction of NAD(+) analogous type ligands such as pbn opens a general pathway for multi-electron reduction of metal complexes via illumination with visible light.

      DOI: 10.1039/c0dt00504e

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    • Photochemical Stereospecific Hydrogenation of a Ru Complex with an NAD(+)/NADH-Type Ligand Peer-reviewed

      Takashi Fukushima, Etsuko Fujita, James T. Muckerman, Dmitry E. Polyansky, Tohru Wada, Koji Tanaka

      INORGANIC CHEMISTRY48 ( 24 ) 11510 - 11512   12 2009

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      A polypyridylruthenium complex with an NAD(+)/NADH model ligand, [Ru(bpy)(2)(pbn)](2+) [bpy = 2,2'-bipyridine, pbn = 2-(2-pyridyl)benzo[b]-1,5-naphthyridine] in a D2O/CH3CN/triethylamine solution, undergoes stereospecific hydrogenation to give Delta-(S)- and Lambda-(R)- [Ru(bpy)(2)(pbnDD)](2+) [pbnDD = 5,10-dideutero-2-(2-pyridyl)benzo[b]-1,5-naphthyridine] upon visible-light irradiation. This result clearly indicates the pathway via the pi-stacked dimer of the deuterated one-electron-reduced species. The reduction of [Ru(bpy)(2)(pbn)](2+) with Na2S2O4 in D2O did not afford any stereospecific products. Furthermore, the more sterically crowded Ru complex, [Ru(dmb)(2)(pbn)](2+) (dmb = 6,6'-dimethyl-2,2'-bipyridine), did not produce the corresponding pbnDD species upon irradiation.

      DOI: 10.1021/ic901935u

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    • Characterization of Redox States of Ru(OH2)(Q)(tpy)(2+) (Q=3,5-di-tert-butyl-1,2-benzoquinone, tpy=2,2 ':6 ',2 ''-terpyridine) and Related Species through Experimental and Theoretical Studies Peer-reviewed

      Ming-Kang Tsai, Jonathan Rochford, Dmitry E. Polyansky, Tohru Wada, Koji Tanaka, Etsuko Fujita, James T. Muckerman

      INORGANIC CHEMISTRY48 ( 10 ) 4372 - 4383   5 2009

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      The redox states of Ru(OH2)(Q) (tpy)(2+) (Q = 3,5-di-tert-butyl-1,2-benzoquinone, tpy = 2,2':6',2 ''-terpyridine) are investigated through experimental and theoretical UV-vis spectra and Pourbaix diagrams. The electrochemical properties are reported for the species resulting from deprotonation and redox processes in aqueous solution. The formal oxidation states of the redox couples in the various intermediate complexes are systematically assigned using electronic structure theory. The controversy over the electronic assignment of ferromagnetic vs. antiferromagnetic coupling is investigated through comparison of ab initio methods and the broken-symmetry density functional theory (DFT) approach. The various pK(a) values and reduction potentials, including the consideration of proton-coupled electron-transfer (PCET) processes, are calculated, and the theoretical version of the Pourbaix diagram is constructed in order to elucidate and assign several previously ambiguous regions in the experimental diagram,

      DOI: 10.1021/ic900057y

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    • Water oxidation by a ruthenium complex with noninnocent quinone ligands: Possible formation of an O-O bond at a low oxidation state of the metal Peer-reviewed

      James T. Muckerman, Dmitry E. Polyansky, Tohru Wada, Koji Tanaka, Etsuko Fujita

      INORGANIC CHEMISTRY47 ( 6 ) 1787 - 1802   3 2008

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      Tanaka and co-workers reported a novel dinuclear Ru complex, [Ru-2(OH)(2)(3,6-Bu(2)Q)(2)(btpyan)](SbF6)(2) (3,6-Bu(2)Q = 3,6-ditert-butyl-1,2-benzoquinone, btpyan = 1,8-bis(2,2':6',2"-terpyrid-4'-yl)anthracene), that contains redox active quinone ligands and has an excellent electrocatalytic activity for water oxidation when immobilized on an indium-tin-oxide electrode (Inorg. Chem., 2001, 40, 329-337). The novel features of the dinuclear and related mononuclear Ru species with quinone ligands, and comparison of their properties to those of the Ru analogues with the bpy ligand (bpy = 2,2'-bipyridine) replacing quinone, are summarized here together with new theoretical and experimental results that show striking features for both the dinuclear and mononuclear species. The identity and oxidation state of key mononuclear species, including the previously reported oxyl radical, have been reassigned. Our gas-phase theoretical calculations indicate that the Tanaka Ru-dinuclear catalyst seems to maintain predominantly Ru(II) centers while the quinone ligands and water moiety are involved in redox reactions throughout the entire catalytic cycle for water oxidation. Our theoretical study identifies [Ru-2(O-2(-))(Q(-1.5))(2)(btpyan)](0) as a key intermediate and the most reduced catalyst species that is formed by removal of all four protons before four-electron oxidation takes place. While our study toward understanding the complicated electronic and geometric structures of possible intermediates in the catalytic cycle is still in progress, the current status and new directions for kinetic and mechanistic investigations, and key issues and challenges in water oxidation with the Tanaka catalyst (and its analogues with Cl- or NO2- substituted quinones and a species with a xanthene bridge instead an antheracene) are discussed.

      DOI: 10.1021/ic701892v

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    • Generation of a Ru-II-semiquinone-anilino-radical complex through the deprotonation of a Ru-III-semiquinone-anilido complex Peer-reviewed

      Yuji Miyazato, Tohru Wada, James T. Muckerman, Etsuko Fujita, Koji Tanaka

      ANGEWANDTE CHEMIE-INTERNATIONAL EDITION46 ( 30 ) 5728 - 5730   2007

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:WILEY-V C H VERLAG GMBH  

      Aminyl radicals may one day be useful oxidn. catalysts if their thermodn. instability can be overcome, for example, through complexation with a metal. Deprotonation of the semiquinonato-anilido complex [RuIII(NHPh-bpa)(tBu2sq)]+ (1; NHPh-bpa = 2-(bis(pyridylmethyl)aminomethyl)-anilido ligand; tBu2sq- = 3,5-di-tert-butylsemiquinonate) leads to formation of the semiquinonato-anilino-radical complex [RuII(·NPh-bpa)(tBu2sq)] (2). Electrochem. redn. of 2 leads to formation of the catecholato-anilino radical complex [RuII(·NPh-bpa)(tBu2cat)]- (3). Treatment of 1 with MeSO3H gave the semiquinone-aniline complex [RuIII(NH2Ph-bpa)(tBu2sq)]2+ (4). The complexes were studied using cyclic voltammetry, EPR, magnetic susceptibility and DFT calcns.

      DOI: 10.1002/anie.200701600

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    • Generation of a Ru-II-semiquinone-anilino-radical complex through the deprotonation of a Ru-III-semiquinone-anilido complex Peer-reviewed

      Yuji Miyazato, Tohru Wada, James T. Muckerman, Etsuko Fujita, Koji Tanaka

      ANGEWANDTE CHEMIE-INTERNATIONAL EDITION46 ( 30 ) 5728 - 5730   2007

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      DOI: 10.1002/anie.200701600

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    • Electrochemical and photochemical behavior of a ruthenium(II) complex bearing two redox sites as a model for the NAD(+)/NADH redox couple Peer-reviewed

      Hidenori Tannai, Take-aki Koizumi, Tohru Wada, Koji Tanaka

      ANGEWANDTE CHEMIE-INTERNATIONAL EDITION46 ( 37 ) 7112 - 7115   2007

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:WILEY-V C H VERLAG GMBH  

      The mononuclear Ru(II) complex, [Ru(bbnp)(terp)]2+ (bbnp = 2,6-bis(benzo[b]-1,5-naphthyridin-6-yl)-4-tert-butylpyridine and terpy = 2,2:6',2''-terpyridine) is reversibly converted into the 4-electron-reduced form [1-H4]2+ through electrochem. and photochem. redox reactions in aq. soln. The 2,6-bis(benzo[b]-1,5-naphthyridin-6-yl)-4-tert-butylpyridine ligand acts alternatively as a reservoir/source of 4 electrons or 4 protons.

      DOI: 10.1002/anie.200701204

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    • Photochemical and radiolytic production of an organic hydride donor with a Ru-II complex containing an NAD(+) model ligand Peer-reviewed

      Dmitry Polyansky, Diane Cabelli, James T. Muckerman, Etsuko Fujita, Take-aki Koizumi, Takashi Fukushima, Tohru Wada, Koji Tanaka

      ANGEWANDTE CHEMIE-INTERNATIONAL EDITION46 ( 22 ) 4169 - 4172   2007

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:WILEY-V C H VERLAG GMBH  

      The photochem. and electrochem. properties of a polypyridylruthenium complex with an NAD+/NADH (NAD+ = NAD) model ligand, [Ru(bpy)2-(pbn)]2+ ([1]2+; bpy = 2,2'-bipyridine, pbn = 2-(2-pyridyl)benzo[b]-1,5-naphthyridine), were investigated. When solns. contg. [1]2+ and triethylamine are irradiated with visible light, [(1)HH]2+ is produced cleanly.

      DOI: 10.1002/anie.200700304

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    • Experimental and Theoretical Evaluation of the Charge Distribution over the Ruthenium and Dioxolene Framework of [Ru(OAc)(dioxolene)(terpy)] (terpy = 2,2':6',2''-terpyridine) Depending on the Substituents. (共著) Peer-reviewed

      Wada, T, Yamanaka, M, Fujihara, T, Miyazato, Y, Tanaka, K

      Inorganic Chemistry45 ( 22 ) 8887 - 8894   12 2006

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    • Experimental and theoretical evaluation of the charge distribution over the ruthenium and dioxolene framework of [Ru(OAc)(dioxolene)(terpy)] (terpy) 2,2 ': 6 ', 2 ''-terpyridine) depending on the substituents Peer-reviewed

      Tohru Wada, Masahiro Yamanaka, Tetsuaki Fujihara, Yuji Miyazato, Koji Tanaka

      INORGANIC CHEMISTRY45 ( 22 ) 8887 - 8894   10 2006

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      A series of ruthenium complexes [ Ru( OAc)( dioxolene)( terpy)] having various substituents on the dioxolene ligand ( dioxolene) 3,5-t-Bu2C6H2O2 ( 1), 4-t-BuC6H3O2 ( 2), 4-ClC6H3O2 ( 3), 3,5-Cl2C6H2O2 ( 4), Cl4C6O2 ( 5); terpy) 2,2': 6'2 ''-terpyridine) were prepared. EPR spectra of these complexes in glassy frozen solutions ( CH2Cl2: MeOH = 95: 5, v/v) at 20 K showed anisotropic signals with g tensor components 2.242 > g(1) > 2.104, 2.097 > g(2) > 2.042, and 1.951 > g(3) > 1.846. An anisotropic value, < g > = g(1) - g(3), and an isotropic g value, < g > [( g(1)(2) + g(2)(2) + g(3)(2))/3](1/2), increase in the order 1 < 2 < 3 < 4 < 5. The resonance between the Ru-II( sq) ( sq = semiquinone) and RuIII( cat) ( cat) catecholato) frameworks shifts to the latter with an increase of the number of electron-withdrawing substituents on the dioxolene ligand. DFT calculations of 1, 2, 3, and 5 also support the increase of the Ru spin density ( RuIII character) with an increase of the number of Cl atoms on the dioxolene ligand. The singly occupied molecular orbitals ( SOMOs) of 1 and 5 are very similar to each other and stretch out the Ru - dioxolene frameworks, whereas the lowest unoccupied molecular orbital ( LUMO) of 5 is localized on Ru and two oxygen atoms of dioxolene in comparison with that of 1. Electron-withdrawing groups decrease the energy levels of both the SOMO and LUMO. In other words, an increase in the number of Cl atoms in the dioxolene ligand results in an increase of the positive charge on Ru. Successive shifts in the electronic structure between the RuII( sq) and RuIII( cat) frameworks caused by the variation of the substituents are compatible with the experimental data.

      DOI: 10.1021/ic060696i

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    • Novel platinum-ruthenium dinuclear complex bridged by 2-aminoethanethiol Peer-reviewed

      Rei Okamura, Tohru Wada, Koji Tanaka

      BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN79 ( 10 ) 1535 - 1540   10 2006

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:CHEMICAL SOC JAPAN  

      A platinum-ruthenium dinuclear complex, [(PtCl){RuCl((t)Bu(2)sq)}(btpyxa)](2+) ([2](2+)) (btpyxa = 2,7-di-tert-butyl-9.9-dimethyl-4,5-bis(2,2':6',2 ''-terpyrid-4'-yl)xanthene, (t)Bu(2)sq = 3,5 -di-tert-butyl-1,2-benzosemiquinonateion), in which btpyxa acts as a bridging ligand, was prepared, and its physical properties were compared to those of an analogous dmso complex, [(PtCl){Ru((t)Bu(2)sq)(dmso)}(btpyxa)](2+) ([1](2+)) (dmso = dimethyl sulfoxide). Treatment of complex [1](2+) with an aqueous NaOH solution followed by 2-aminoethanethiol afforded [{Pt(SCH2CH2NH2)}{Ru((t)Bu(2)sq)(dmso))(btpyxa)](2+) ([3](2+)). On the other hand, the reaction of complex [2](2+) with 2-arninoethanethiol produced [{Pt(SCH2CH2NH2)}Ru((t)Bu(2)sq)}(btpyxa)](2+) ([4](2+)), in which Pt and Ru atoms are bridged by the 2-aminoethanethiolato ligand. Complex [4](2+) was also obtained by heating complex [3](2+) in 2-methoxyethanol.

      DOI: 10.1246/bcsj.79.1535

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    • Redox behavior and catalytic oxidation reactions of alcohols by a new ruthenium(III)-dioxolene-amine complex of bis(2-pyridylmethyl)-2-aminoethylamine Peer-reviewed

      Yuji Miyazato, Tohru Wada, Koji Tanaka

      BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN79 ( 5 ) 745 - 747   5 2006

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      A ruthenium-dioxolene-amine complex, [Ru-III(NH2L)(Bu(2)sq)](PF6)(2)center dot 0.5H(2)O (NH2-L = bis(2-pyridylmethyl)2-aminoethylamine, Bu(2)sq(-) = 15-di-tert-butylsemiquinonate). was newly prepared. The complex undergoes spontaneous one-electron reduction under basic conditions in MeOH and works as an electrocatalyst in the oxidation of benzyl alcohol to benzaldehyde under electrolysis at +0.4V (vs SCE).

      DOI: 10.1246/bcsj.79.745

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    • Comparison of basicity of the diimine and quinoid group of 1,10-phenanthroline-5,6-dione ligated on Pt(II) Peer-reviewed

      R Okamura, T Fujihara, T Wada, K Tanaka

      BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN79 ( 1 ) 106 - 112   1 2006

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      A platinum(II) complex bearing 1,10-phenanthroline-5,6-dione (phenO(2)), [PtCl(phenO(2)-N,N')(PPh3)](+) ([2](+)) was newly prepared and characterized. An X-ray crystallographic study of [2](PF6) revealed that the phenO(2) ligand coordinates to platinum with the N,N'-chelate form. The basicity of the quinoid part of phenO(2) in [2](+) and of the diimine one in [Pt(phenO(2)-O,O')(PPh3)(2)] with an O,O'-chelate ring (3) was evaluated in the absence and the presence of Li+ by means of UV-vis spectroscopy and cyclic voltammetry. The quinoid group in [2](+) practically had no ability to bind Li+, but induced on anodic potential shift of the phenO(2) localized redox potential by 850 mV due to the strong interaction between the reduced form of [2](+) and Li+. Undeniably, a weak interaction of Li+ with the diimine moiety of free phenO(2) (K = 3.6 M-1) is greatly enhanced in the interaction between Li+ and the diimine site in 3 because of the electron donation from the catecholato group of the complex.

      DOI: 10.1246/bcsj.79.106

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    • Redox behavior and catalytic oxidation reactions of alcohols by a new ruthenium(III)-dioxolene-amine complex of bis(2-pyridylmethyl)-2-aminoethylamine Peer-reviewed

      Yuji Miyazato, Tohru Wada, Koji Tanaka

      Bulletin of the Chemical Society of Japan79 ( 5 ) 745 - 747   2006

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      A ruthenium-dioxolene-amine complex, [RuIII(NH 2-L)(Bu2sq)](PF6)2·0.5H 2O (NH2-L = bis(2-pyridylmethyl)-2-aminoethylamine, Bu2sq- = 3,5-di-tert-butylsemiquinonate), was newly prepared. The complex undergoes spontaneous one-electron reduction under basic conditions in MeOH and works as an electrocatalyst in the oxidation of benzyl alcohol to benzaldehyde under electrolysis at +0.4 V (vs SCE). © 2006 The Chemical Society of Japan.

      DOI: 10.1246/bcsj.79.745

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    • Novel platinum-ruthenium dinuclear complex bridged by 2-aminoethanethiol Peer-reviewed

      Rei Okamura, Tohru Wada, Koji Tanaka

      Bulletin of the Chemical Society of Japan79 ( 10 ) 1535 - 1540   2006

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      A platinum-ruthenium dinuclear complex, [(PtCl){RuCl( tBu 2sq)}(btpyxa)] 2+ ([2] 2+) (btpyxa = 2,7-di-tert-butyl-9,9-dimethyl-4,5-bis(2,2′:6′,2″-terpyrid- 4′-yl)xanthene, tBu 2sq = 3,5-di-tert-butyl-1,2- benzosemiquinonate ion), in which btpyxa acts as a bridging ligand, was prepared, and its physical properties were compared to those of an analogous dmso complex, [(PtCl){Ru( tBu 2sq)(dmso)}(btpyxa)] 2+ ([1] 2+) (dmso = dimethyl sulfoxide). Treatment of complex [1] 2+ with an aqueous NaOH solution followed by 2-aminoethanethiol afforded [{Pt(SCH 2CH 2NH 2)}{Ru( tBu 2sq)-(dmso)}(btpyxa)] 2+ ([3] 2+). On the other hand, the reaction of complex [2] 2+ with 2-aminoethanethiol produced [{Pt-(SCH 2CH 2NH 2)Ru( tBu 2sq)}(btpyxa)] 2+ ([4] 2+), in which Pt and Ru atoms are bridged by the 2- aminoethanethiolato ligand. Complex [4] 2+ was also obtained by heating complex [3] 2+ in 2-methoxyethanol. © 2006 The Chemical Society of Japan.

      DOI: 10.1246/bcsj.79.1535

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    • Reversible bond formation and cleavage of the oxo bridge of [Ru-2(mu-O)-(dioxolene)(2)(btpyxa)(3+) [btpyxa=2,7-Di-tert-butyl-9,9-dimethyl-4,5bis(2,2 ': 6 ',2 ''-terpyrid-4 '-yl)xanthene] driven by a three-electron redox reaction Peer-reviewed

      T Wada, K Tanaka

      EUROPEAN JOURNAL OF INORGANIC CHEMISTRY19 ( 19 ) 3832 - 3839   10 2005

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:WILEY-V C H VERLAG GMBH  

      The bis(chlororuthenium) complex [RU2Cl2(3,6-tBu(2)sq)(2-)(btpyxa)](PF6)(2) [1](PF6)(2) [3,6-tBu(2)sq = 3,6-di-tert-butyl-1,2-benzosemiquinone; btpyxa = 2,7-di-tert-butyl-9,9-dimethyl-4,5-bis(2,2':6',2"-terpyrid-4'-yl)xanthene] and the oxobridged diruthenium complex [Ru-2(mu-O)(3,6-tBu(2)sq)(2)-(btpyxa)](PF6)(3) [2](PF6)(3) were synthesized, and the redox behavior of these complexes, which contain a non-innocent dioxolene ligand, was investigated by electrochemical and electrospectrochemical methods. Dicationic [1](2+) undergoes two successive metal-centered one-electron and a simultaneous two-electron ligand-based redox reaction at E-1/2 = +0.13 and +0.09 and E-1/2 = -0.75 V (vs. SCE), respectively, in CH2Cl2. The UV/Vis/NIR spectrum of tricationic [2](3+) shows an intervalence-transition (IT) band at 1333 nm (epsilon = 1.52 x 10(4) M-1 cm(-1)) in a near-IR region together with two CT bands at 766 (epsilon = 2.21 x 10(4) M(-1)cm(-1)) and 586nm (c = 1.13 x 104 M-1 cm(-1)) in CH2Cl2. The mixed-valence complex of [2 ](3+) with an Ru-IV-O-Ru-III core is reversibly oxidized and reduced to the Ru-IV-Ru-IV and Ru-ll-Ru-ll oxidation states at E-1/2 = +0.63 and -0.01 V, respectively, in CH2Cl2. On the other hand, three-electron reduction of [2](PF6)(3) is accompanied by the cleavage of the Ru-O-Ru bond at E-p = +0.02 V to give [(Ru(OMe)(3,5-tBU(2)sq))(Ru(OH2)(3,5-tBU(2)sq))(btpyxa)](+) in MeOH. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

      DOI: 10.1002/ejic.200500141

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    • Redox behavior of new Ru-dioxolene-ammine complexes and catalytic activity toward electrochemical oxidation of alcohol under mild conditions Peer-reviewed

      T Hino, T Wada, T Fujihara, K Tanaka

      CHEMISTRY LETTERS33 ( 12 ) 1596 - 1597   12 2004

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      The new Ru-dioxolene-ammine complexes, [Ru-II(NH3)-(sq)(trpy)](ClO4) (1, sq = 3,5-di-tert-butyl-1,2-benzoseiniquinone, trpy = 2,2:6,2"-terpyridine) and [Ru-III(NH3)(sq)(trpy)](ClO4)(2) (2), were prepared. They have an ability to oxidize MeOH and i-PrOH catalytically under very mild conditions such as the electrolysis at 0V (vs SCE) in CH2Cl2.

      DOI: 10.1246/cl.2004.1596

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    • A platinum-ruthenium dinuclear complex bridged by bis(terpyridyl)xanthene Peer-reviewed

      R Okamura, T Wada, K Aikawa, T Nagata, K Tanaka

      INORGANIC CHEMISTRY43 ( 22 ) 7210 - 7217   11 2004

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      4,5-Bis(terpyridyl)-2,7-di-tert-butyl-9,9-dimethylxanthene (btpyxa) was prepared to serve as a new bridging ligand via Suzuki coupling of terpyridin-4'-yl triflate and 2,7-di-teil-butyl-9,9-dimethylxanthene-4,5-diboronic acid. The reaction of btpyxa with either 1 equiv or an excess of PtCl2(cod) (cod = 1,5-cyclooctadiene) followed by anion exchange afforded mono- and dinuclear platinum complexes [(PtCl)(btpyxa)](PF6) ([1](PFO) and [(PtCl)(2)(btpyxa)](PF6)(2) ([2]-(PF6)(2)), respectively. The X-ray crystallography of [1](PF6)-CHCl3 revealed that the two terpyridine units in the ligand are nearly parallel to each other. The heterodinuclear complex [(PtCl){Ru((t)Bu(2)SQ)(dmso)}(btpyxa)](PF6)(2) ([4](PF6)(2)) (dmso = dimethyl sulfoxide; (t)Bu(2)SQ = 3,5-di-tert-butyl-1,2-benzosemiquinone) and the monoruthenium complex [Ru((t)Bu(2)SQ)(dmso)(trpy)](PF6) ([5](PF6)) (trpy = 2,2':6',2"-terpyridine) were also synthesized. The CV of [2](2+) suggests possible electronic interaction between the two Pt(trpy) groups, whereas such an electronic interaction was not suggested by the CV of [4](2+) between Pt(trpy) and Ru((t)Bu(2)SQ) frameworks.

      DOI: 10.1021/ic049680n

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    • Strong interaction between carbonyl and dioxolene ligands caused by charge distribution of ruthenium-dioxolene frameworks of mono- and dicarbonylruthenium complexes Peer-reviewed

      T Wada, T Fujihara, M Tomori, D Ooyama, K Tanaka

      BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN77 ( 4 ) 741 - 749   4 2004

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      Monocarbonylruthenium complexes with a semiquinone ligand, ([Ru(CO)(sq)(L)(n+) (sq = 3,5-di-tert-butyl-1,2-benzosemiquinone. n = 1 or 0. L = 2,2':6',2"-terpyridine ([1](+)), 2,6-bis(N,N-dimethyIaminomethyl)pyridine ([2](+)), 2.6-di-2'-pyridylphenyl ([3](0)), or 2-(2,2'-bipyridin-6-yl)phenolato ([4](0))), and dicarbonylruthenium complexes with two semiquinone ligands, [Ru(CO2)(2)(sq)(2)] ([5](0)) and [Ru(CO)(2)(phsq)(2)] (phsq = 9,10-phenanthrasemiquinone, [6](0)), were synthesized and the structures of [1](+) and [6] were determined by X-ray crystal analysis. Monocarbonyl Ru(II)-dioxolene complexes displayed the ligand localized catecholato/semiquinone and semiquinone/quinone redox couples, and two sets of those redox couples were observed in the dicarbonyl Ru(II)-bis(dioxolene) complexes. Spectroelectrochemical study revealed that the Ru(II)-catecholato and Ru(II)-semiquinone complexes were stable in solutions, while the Ru(II)-quinone complexes underwent fragmentation in solutions. One-electron reduction of the rnonocarbonyl Ru(II)- was substantially larger semiquinone complexes caused a red shift of the nu(CO) bands in a range of 41 to 56 cm(-1), which was substantially larger than those of carbonyl Ru(II)-polypyridyl complexes. Two nu(CO) bands of dicarbonyl Ru(II)-bis(semiquinone) complexes also shifted to lower wavelength in a range of 53 to 99 cm(-1) upon two electron reduction of the complexes. The unusually large red shift of nu(CO) bands upon reduction of carbonyl Ru(II)-dioxolene complexes compared with those of Ru(II)-polypyridyl complex is ascribed to a strong electronic interaction between carbonyl and dioxolene ligands.

      DOI: 10.1246/bcsj.77.741

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    • Syntheses and electrochemical properties of ruthenium(II) complexes with 4,4 '-bipyrimidine and 4,4 '-bipyrimidinium ligands Peer-reviewed

      T Fujihara, T Wada, K Tanaka

      INORGANICA CHIMICA ACTA357 ( 4 ) 1205 - 1212   3 2004

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:ELSEVIER SCIENCE SA  

      The syntheses and electrochemical properties of novel ruthenium(II) polypyridyl complexes with 4,4'-bipyrimidine, [Ru(trpy)(bpm)Cl](X) ([1](X; X = PF6-, BF4-)) and with a quaternized 4,4'-bipyrimidinium ligand, [Ru(trpy)(Me(2)bpm)Cl](BF4)(3) ([2](BF4)3) (trpy = 2,2':6',2"-terpyridine, bpm = 4,4'-bipyrimidine, Me(2)bpm = 1,1'-dimethyl-4,4'-bipyrimidinium) are presented. The bpm complex [1](divided by) was prepared by the reaction of Ru(trpy)Cl-3 with 4,4'-bipyrimidine in EtOH/H2O. The structural characterization of [1](divided by) revealed, that the bpm ligand coordinated to the ruthenium atom with the bidentate fashion. Diquaternization of the noncoordinating nitrogen atoms on bpm of [1](divided by) by (CH3)(3)OBF4 in CH3CN gave [2](BF4)(3). The electrochemical and spectroelectrochemical properties of the complexes are described. (C) 2003 Elsevier B.V. All rights reserved.

      DOI: 10.1016/j.ica.2003.10.015

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    • Acid-base equilibria of various oxidation states of aqua-ruthenium complexes with 1,10-phenanthroline-5,6-dione in aqueous media Peer-reviewed

      T Fujihara, T Wada, K Tanaka

      DALTON TRANSACTIONS ( 4 ) 645 - 652   2004

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:ROYAL SOC CHEMISTRY  

      Syntheses and pH dependent electrochemical properties of aqua-ruthenium(II) complexes, [Ru(trpy)(PDA-N,N')-(OH2)](ClO4)(2) ([1](ClO4)(2)) and [Ru(trpy)(PD-N,N')(OH2)](ClO4)(2) ([2](ClO4)(2)) (trpy = 2,2':6',2"-terpyridine, PDA = 6-acetonyl-6-hydroxy-1,10-phenanthroline-5-one, PD = 1,10-phenanthroline-5,6-dione) are presented. Treatment of [Ru(trpy)(PD-N,N')Cl](PF6) with AgClO4 in a mixed solvent of acetone and H2O selectively produced the acetonyl-PD complex [1](ClO4)(2), and the similar treatment in a mixed solvent of 2-methoxyethanol and H2O gave the PD complex[2](ClO4)(2). The molecular structures of both complexes were determined by X-ray structural analysis. The proton dissociation constants of various oxidations state of [1](2+) and [2](2+) were evaluated by simulation of E-1/2 values of those redox potentials depending on pH. The simulation revealed that the acetonyl-PD complex[1](2+) underwent successive Ru(II)/Ru(III) and Ru(III)/Ru(IV) redox couples though the two redox reactions were not separated in the cyclic voltammograms. The redox behavior of [2](2+) in H2O is reasonably explained by not only the similar successive metal-centered redox reactions but also simultaneous two-electron quinone/catechol redox couple of the PD ligand including the contribution of hydration on a carbonyl carbon.

      DOI: 10.1039/b312310c

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    • Coordination ability of 1,10-phenanthroline-5,6-dione: syntheses and redox behavior of a Ru(II) complex with an o-quinoid moiety and of bridged Ru(II)-M(II) complexes (M = Pd, Pt) Peer-reviewed

      T Fujihara, R Okamura, T Wada, K Tanaka

      DALTON TRANSACTIONS ( 16 ) 3221 - 3226   8 2003

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:ROYAL SOC CHEMISTRY  

      The synthesis and electrochemical properties of a Ru(II) complex having a redox active ligand, 1,10-phenanthroline-5,6-dione, [Ru(trpy)(PD-N,N')Cl](PF6) ([1](PF6)), and mixed-metal complexes [(PPh3)(2)Pd(O,O'-PD-N,N')Ru(trpy)-Cl](PF6) ([2](PF6)) and [(PPh3)(2)Pt(O,O'-PD-N,N')Ru(trpy)Cl](PF6) ([3](PF6)) (trpy = 2,2':6',2"-terpyridine, PD = 1,10-phenanthroline-5,6-dione) are presented. The complex of [1](+), which was prepared by the reaction of Ru(trpy)(DMSO)Cl-2 with PD in hot ethanol, underwent two reversible reductions in the PD-based redox reactions. The quinoid moiety of [1](+) was endowed with coordination ability to metals by one- and two-electron reduction of the complex. The mixed-metal complexes of [2](+) and [3](+) were synthesized by the reactions of [1](+) with M(PPh3)(4) (M = Pd, Pt), and both complexes have the [1](-) and M(II) frameworks.

      DOI: 10.1039/b304912d

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    • Characterization of a stable ruthenium complex with an oxyl radical Peer-reviewed

      K Kobayashi, H Ohtsu, T Wada, T Kato, K Tanaka

      JOURNAL OF THE AMERICAN CHEMICAL SOCIETY125 ( 22 ) 6729 - 6739   6 2003

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER CHEMICAL SOC  

      The ruthenium oxyl radical complex, [Ru-II(trpy)(Bu(2)SQ)O.-] (trpy = 2,2':6',2"-terpyridine, Bu-2-SQ = 3,5-di-tert-butyl-1,2-benzosemiquinone) was prepared for the first time by the double deprotonation of the aqua ligand of [Ru-III(trpy)(Bu(2)SQ)(OH2)](ClO4)(2), [Ru-III(trpy)(BU2SQ)(OH2)](ClO4)(2) is reversibly converted to [Ru-III(trpy)(Bu(2)SQ)(OH-)](+) upon dissociation of the aqua proton (pK(a) 5.5). Deprotonation of the hydroxo proton gave rise to intramolecular electron transfer from the resultant O2- to Ru-dioxolene. The resultant [Ru-II(trpy)(Bu(2)SQ)O.-] showed antiferromagnetic behavior with a Ru-II-semiquinone moiety and oxyl radical, the latter of which was characterized by a spin trapping technique. The most characteristic structural feature of [Ru-II(trpy)(Bu(2)SQ)O.-] is a long Ru-O bond length (2.042(6) Angstrom) as the first terminal metal-O bond with a single bond length. To elucidate the substituent effect of a quinone ligand, [Ru-III(trpy)(Bu(2)SQ)(OH2)](ClO4)(2) (4CISQ = 4-chloro-1,2-benzosemiquinone) was prepared and we compared the deprotonation behavior of the. aqua ligand with that of [Ru-III(trpy)(Bu(2)SQ)(OH2)](ClO4)(2). Deprotonation of the aqua ligand of [Ru-III(trpy)(4CISQ)(OH2)](ClO4)(2) induced intramolecular electron transfer from OH- to the [Ru-III-(4CISQ)] moiety affording [Ru-II(trpy)(4CISQ)(OH.)](+), which then probably changed to [Ru-II(trpy)(4CISQ)O.-]. The antiferromagnetic interactions. (J values) between Ru-II-semiquinone and the oxyl radical for [Ru-II(trpy)(Bu(2)SQ)O.-] and for [Ru-II(trpy)(4CISQ)O.-] were 2J = -0.67 cm(-1) and -1.97 cm(-1), respectively.

      DOI: 10.1021/ja0211510

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    • Ruthenium oxyl radical complex containing o-quinone ligand detected by ESR measurements of spin trapping technique Peer-reviewed

      K Kobayashi, F Ohtsu, T Wada, K Tanaka

      CHEMISTRY LETTERS ( 8 ) 868 - 869   8 2002

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:CHEMICAL SOC JAPAN  

      Ruthenium-quinone complex containing an aqua ligand, [Ru-II(trpy)(35tBu(2)Q)(OH2)](ClO4)(2) (trpy=2,2':6',2"-terpyridine, 35tBu(2)Q=3,5-di-tert-butyl-1,2-benzoquinone) underwent deprotonation of an aqua ligand accompanied with intramolecular electron transfer from O2- ligand to quinone ligand generating O.- ligand.

      DOI: 10.1246/cl.2002.868

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    • Novel diruthenium disulfinate complex formed by oxygen capture on deprotonated form of ruthenium-aqua-dithiolene: Four oxygens from O-2 and four oxygens from H2O Peer-reviewed

      H Sugimoto, H Wada, Y Wakatsuki, T Wada, K Tanaka

      CHEMISTRY LETTERS ( 6 ) 634 - 635   6 2002

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:CHEMICAL SOC JAPAN  

      Oxygenation of sulfur in ruthenium-dithiolene complex took place in CH3OH/H2O in the air and the novel diruthenium disulfinate complex formed. The similar oxygenation by use of O-18(2) and H-2 O-18 revealed that four of the eight oxygen of disulfinate complex resulted from O-2 and the remaining four came from H2O.

      DOI: 10.1246/cl.2002.634

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    • A Ru-carbene complex with a metallacycle involving a 1,8-naphthylidine framework Peer-reviewed

      T Tomon, D Ooyama, T Wada, K Shiren, K Tanaka

      CHEMICAL COMMUNICATIONS ( 12 ) 1100 - 1101   6 2001

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:ROYAL SOC CHEMISTRY  

      The reaction of [Ru(bpy)(2)(napy-kappa N-2,N')](PF6)(2) [1](PF6)(2) (napy = 1,8-naphthyridine) with propiolic acid yielded a Ru-carbene complex with a five-membered metallacycle involving a 1,8-naphthylidine framework.

      DOI: 10.1039/b101045j

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    • Studies on Bis(hydroxoruthenium)complexes with Quinones as Non-innocent Ligands and Their Catalytic Abilities for Oxidation Reactions Peer-reviewed

      Tohru Wada

          20 3 2001

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      Language:English   Publishing type:Doctoral thesis  

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    • Preparation and reductive elimination of digermylplatinum complexes Peer-reviewed

      Kunio Mochida, Tohru Wada, Wakako Hatanaka, Yuriko Nishiyama, Michiko Suzuki, Masato Nanjo

      Main Group Metal Chemistry24 ( 9 ) 647 - 652   2001

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:Walter de Gruyter GmbH  

      cis- and trans-(R3Ge)2Pt(PMe2Ph)2 complexes as key intermediates of bis-germylation of alkynes have been prepared, and their structures have been established by spectroscopic methods and X-ray crystallography. The cis isomers afford digermanes, (R3Ge)2 as reductive elimination products in good yields. In contrast, the trans isomers lead to monogermanes.

      DOI: 10.1515/MGMC.2001.24.9.647

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    • Platinum-catalyzed bis-germylation of alkynes with organodigermanes and cyclic oligogermanes Peer-reviewed

      K Mochida, T Wada, K Suzuki, W Hatanaka, Y Nishiyama, M Nanjo, A Sekine, Y Ohashi, M Sakamoto, A Yamamoto

      BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN74 ( 1 ) 123 - 137   1 2001

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:CHEMICAL SOC JAPAN  

      Hexamethyldigermane, Me3CeGeMe3, reacted with various alkynes in the presence of platinum complexes at 120 degreesC to afford Z-1,2-bis(germyl)ethenes in moderate to good yields. Terminal alkynes exhibit higher reactivities than internal ones. [Pt(acac)(2)] and [Pt(dba)(2)] serve as efficient catalysts, while [Pt(PPh3)(4)], [PtCl2(PPh3)(2)], and [Pt(dba)(2)]-phosphite were found to be inactive. Four- and six-membered cyclic oligogermanes, such as dodecamethylcyclohexagermane. (Me2Ge)(6), reacted with alkynes in the presence of platinum catalysts to yield 1,4-digermacyclohexa-2,5-dienes in ca. 30% yield. The reactions of phenylacetylene with 1,2-digermacyclohexa-3,5-dienes afforded the corresponding 1,4-digermacyclohexa-2,5,7-trienes in 93% yield. Bis(germyl)platinum complexes having various tertiary phosphine ligands have been prepared as models of a key intermediate in the above mentioned catalytic bis-germylation of alkynes, and their structures have been established by spectroscopic methods and X-ray crystallography. Bis(germyl)platinum complexes reacted with phenylacetylene to give the corresponding insertion products, germyl(germylvinyl)platinum species, whose structures have been determined by spectroscopic and X-ray analysis. Germyl(germylvinyl)platinum complexes were found to liberate a bis-germylation product of the alkyne upon heating. The result supports a mechanism involving the oxidative addition of a digermane to a Pt(0) complex, the insertion of an alkyne into one of the two Pt-Ge bonds to give a germyl(germylvinyl)platinum species, and the reductive elimination of the bis-germylation product of the alkyne. Evidence suggesting the extrusion of a germylene unit from the bis-germylplatinum species has been obtained, accounting for the generation courses of other by-products.

      DOI: 10.1246/bcsj.74.123

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    • Syntheses and redox properties of bis(hydroxoruthenium) complexes with quinone and bipyridine ligands. Water-oxidation catalysis Peer-reviewed

      T Wada, K Tsuge, K Tanaka

      INORGANIC CHEMISTRY40 ( 2 ) 329 - 337   1 2001

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER CHEMICAL SOC  

      The novel bridging ligand 1,8-bis(2,2':6',2"-terpyridyl)anthracene (btpyan) is synthesized by three reactions from 1,8-diformylanthracene to connect two [Ru(L)(OH)](+) units (L = 3,6-di-tert-butyl-1,2;benzoquinone (3,6-Bu-t(2)-qui) and 2,2'-bipyridine (bpy)). An addition of (BuOK)-Bu-t (2.0 equiv) to a methanolic solution of [Ru-2(II)(OH)(2)(3,6-(t)Bu(2)qui)(2)(btpyan)](SbF6)(2) ([1](SbF6)(2)) results in the generation of [Ru-2(II)(O)(2)(3,6-(t)Bu(2)sq)(2)(btpyan)](0) (3,6-(t)Bu(2)sq = 3,6 -di-tert-butyl-1,2-semiquinone) due to the reduction of quinone coupled with the dissociation of the hydroxo protons. The resultant complex [Ru-2(II)(O)(2)(3,6-(t)Bu(2)sq)(2)(btpyan)](0) undergoes ligand-localized oxidation at E-1/2 = +0.40 V (vs Ag/AgCl) to give [Ru-2(II)(O)(2)(3,6-(t)Bu(2)qui)(2)(btpyan)](2+) in MeOH solution: Furthermore, metal-localized oxidation of [Ru-2(II)(O)(2)(3, 6-(t)Bu(2)qui)(2)(btpyan)](2+) at E-p = + 1.2 V in CF3CH2OH/etheq or water gives [Ru-2(III)(O)(2)(3,6-(t)Bu(2)qui)(2)(btpyan)](4+), which catalyzes water oxidation. Controlled-potential electrolysis of [1](SbF6)(2) at +1.70 V in the presence of H2O in CF3CH2OH evolves dioxygen with a current efficiency of 91% (21 turnovers). The turnover number of O-2 evolution increases to 33 500 when the electrolysis is conducted in water (pH 4.0) by using a [1](SbF6)(2)-modified ITO electrode. On the other hand, the analogous complex [Ru-2(II)(OH)(2)(bpy)(2)(btpyan)](SbF6)(2) ([2](SbF6)(2)) shows neither dissociation of the hydroxo protons, even in the presence of a large excess of (BuOK)-Bu-t, nor activity for the oxidation of H2O under similar conditions.

      DOI: 10.1021/ic000552i

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    • Oxidation of hydrocarbons by mono- and dinuclear ruthenium quinone complexes via hydrogen atom abstraction Peer-reviewed

      T Wada, K Tsuge, K Tanaka

      CHEMISTRY LETTERS ( 8 ) 910 - 911   8 2000

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:CHEMICAL SOC JAPAN  

      Deprotonation and two-electron oxidation of [Ru-2(II)(OH)(2)(Q)(2)(btpyan)](2+) (Q = 3,6-di(tert-butyl)-1,2-quinone, btpyan = 1,8-bis(2,2':6',2"-terpyridyl)anthracene) was converted to bis(ruthenium-oxo) complex [Ru-2(II)(O)(2)(Q)(2)(btpyan)](2+), which oxidized 1,3-cychrohexadiene and 1,2-dihydronaphtalene to corresponding aromatic compounds in the presence of AgClO4 and t-BuOK. On the other hand, mononuclear complex [Ru-II(OH2)(Q)(Ph-terpy)](2+) (Ph-terpy = 4'-phenyl-2,2': 6',2"-terpyridine, [2](2+)) was converted to [Ru-II(OH)(Q)(Ph-terpy)](2+) under the similar conditions, but displayed the low activity for the oxidation compared with the dinuclear complex [1](2+).

      DOI: 10.1246/cl.2000.910

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    • Electrochemical oxidation of water to dioxygen catalyzed by the oxidized form of the bis(ruthenium-hydroxo) complex in H2O Peer-reviewed

      T Wada, K Tsuge, K Tanaka

      ANGEWANDTE CHEMIE-INTERNATIONAL EDITION39 ( 8 ) 1479 - +   2000

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:WILEY-V C H VERLAG GMBH  

      Electrochem. oxidn. of water is catalyzed by an ITO electrode modified with a bis(ruthenium-hydroxo) complex. This ruthenium complex is prepd. by reacting RuCl3 with 1,8-bis(terpyridyl)anthracene (btpyan) in MeOH, treating [Ru2Cl6(btpyan)] with 3,6-di-tert-butyl-1,2-benzenediol in the presence of KOAc in MeOH. This [RuII 2(OAc)(3,6-tBu2sq)2(btpyan)]+ (3,6-tBu2sq = 3,6-di(tert-butyl)-1,2-semiquinone) was treated with triflic acid in MeOH contg. water and then sodium hexafluoroantimonate to give [Ru2(OH)2(3,6-tBu2qui)2(btpyan)](SbF6)2. When a controlled-potential electrolysis for this complex on ITO electrode was conducted at +1.7 V (vs. Ag/AgCl) in water, 1.1 mL of O2 evolved after 20.2 C had passed in the electrolysis. The current efficiency for O2 evolution was 95%.

      DOI: 10.1002/(SICI)1521-3773(20000417)39:8<1479::AID-ANIE1479>3.0.CO;2-4

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    • Thermal ring contraction of 1,2-digermacyclohexadienes coordinated with iron tricarbonyl fragment Peer-reviewed

      K Mochida, W Hatanaka, T Wada, A Sekine, Y Ohashi, A Yamamoto

      CHEMISTRY LETTERS ( 10 ) 991 - 992   10 1998

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      Language:English   Publishing type:Research paper (scientific journal)   Publisher:CHEMICAL SOC JAPAN  

      1, 1, 2, 2-Tetraalkyl-3, 6-diphenyl-1, 2-digermacyclohexa-3, 5-dienes (1) reacted with iron pentacarbonyl to give the corresponding tricarbonyl(eta(4)-1,1,2,2-tetraalkyl-3,6-diphenyl-1,2-digermacyclohexa-3,5-diene)iron (2). Heating 2 caused extrusion of dialkylgermylenes to give (eta(4)-1,1-dialkyl-2,5-diphenyl-1-germacyclopenta-2,4-diene)tricarbonyliron (3). The structures of the (diene)iron tricarbonyls were determined by X-ray crystal structure analysis.

      DOI: 10.1246/cl.1998.991

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    Misc.

    • Preparation and reductive elimination of digermylplatinum complexes

      K Mochida, T Wada, W Hatanaka, Y Nishiyama, M Suzuki, M Nanjo

      MAIN GROUP METAL CHEMISTRY24 ( 9 ) 647 - 652   2001

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      Language:English   Publisher:FREUND PUBLISHING HOUSE LTD  

      cis- and trans-(R3Ge)(2)Pt(PMe2Ph)(2) complexes as key intermediates of bis-germylation of alkynes have been prepared, and their structures have been established by spectroscopic methods and X-ray crystallography. The cis isomers afford digermanes, (R3Ge)(2) as reductive elimination products in good yields. In contrast, the trans isomers lead to monogermanes.

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    Books and Other Publications

    • Molecular Water Oxidation Catalysis

      Wada, Tohru, Tanaka, Koji, Muckerman, James T, Fujita, Etsuko( Role: Joint author)

      John Wiley & Sons Ltd.  2015  ( ISBN:9781118413371

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      Language:English Book type:Scholarly book

      This article discusses about the water oxidn. catalyzed by dinuclear ruthenium catalysts with non-innocent ligands. Describe electrocatalytic water oxidn. by the Tanaka catalyst and a related [Ru2(μ-Cl(bpy)2(btpyan))]3+ ([1Cl(bpy)2]3+), which is a precatalyst of the water oxidn. catalyst [Ru2 III(OH)2(bpy)2(btpyan)]4+ ([(OH)2(bpy)2]4+), then explain the acid-base equil. and redox behavior of mononuclear Ru-aqua complexes with a variety of dioxolene ligands, since a dioxolene ligand on the ruthenium has substantial effects on the electronic state and catalytic activity of the ruthenium complexes.

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    • 実験化学講座22巻—金属錯体、遷移金属錯体クラスター−

      和田 亨, 田中 晃二( Role: Joint author)

      丸善  2004  ( ISBN:4621073214

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      Language:Japanese Book type:Dictionary, encyclopedia

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    Professional Memberships

    Research Projects

    • Photochemical carbon dioxide reduction reaction catalyzed by transition-metal complexes based on binuclear structure

      Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research 

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      4 2021 - 3 2024

      Grant number:21K05102

      Grant amount:\4160000 ( Direct Cost: \3200000 、 Indirect Cost:\960000 )

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    • Development of Ruthenium Water Oxidation Catalysts Inspired by Natural Photosynthesis Mechanism

      Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area) 

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      4 2020 - 3 2022

      Grant number:20H05116

      Grant amount:\6500000 ( Direct Cost: \5000000 、 Indirect Cost:\1500000 )

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    • Construction of a Novel Reduction Catalytic System Using a Pt(II)/Pt(III) Redox Pair

      Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research 

      WADA Tohru

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      4 2018 - 3 2021

      Grant number:18K05158

      Authorship:Principal investigator  Grant type:Competitive

      Grant amount:\4290000 ( Direct Cost: \3300000 、 Indirect Cost:\990000 )

      We have prepared a Pt(IV) complex having a 1,4,7-triazacyclononane and revealed that two-electron reduction of the complex and oxidation reactions of the reduced form proceed via a different process. The isolated square-planar Pt(II) complex reacted with bromine or iodine to provide the corresponding Pt(IV) complex quantitatively. This reaction proceeds via electron transfer from Pt(II) complex to bromine or iodine followed by coordination of a halide ion to Pt(IV) complex. This research has successfully demonstrated that Pt complex, which is generally redox inert, become be active for redox reactions by introduction of 1,4,7-triazacyclononane.

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    • 光合成のPCET機能を模倣したルテニウム錯体による高効率光酸素発生系の構築

      日本学術振興会  科学研究費助成事業 新学術領域研究(研究領域提案型) 

      和田 亨

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      4 2018 - 3 2020

      Grant number:18H05179

      Grant amount:\5200000 ( Direct Cost: \4000000 、 Indirect Cost:\1200000 )

      天然の光合成では、Photosystem IIに存在するマンガンとカルシウム、酸素から構成されるクラスターが水の酸化反応を触媒している。近年、Photosystem IIの高精度の結晶構造解析が報告され、このマンガンクラスターが近傍に存在するチロシン残基と水素結合していることが明らかにされた。チロシン残基のフェノールは、光増感の役割をしているクロロフィルP640とマンガンクラスターとの間の電子移動に重要な役割をしている。本研究では、この天然光合成におけるチロシン残基がマンガンクラスターの酸素発生触媒活性の向上に関わっているとの予想に基づき、人工的な水の酸化触媒であるルテニウム錯体にフェノール基を導入した新規錯体触媒[Ru(OH2)(bpy)(thaq)]2+ (bpy = 2,2'-ビピリジン、thaq = 1,8-(2,4-ジ-tert-ブチルヒドロキシフェニル)アントラキノン)を合成した。平衡電極電位近傍での電気化学的な水の酸化反応を実現すると共に、水の酸化反応におけるフェノール部位の役割を明らかにすることを目的とする。本反応系におけるフェノール部位の役割を解明することは、天然の光合成の反応機構解明にも寄与するものと考えている。[Ru(OH2)(bpy)(thaq)](PF6)2を電極上に塗布して作成した修飾電極を用いて電気化学的な水の酸化反応について検討を行ったところ、フェノール部位を持たない錯体触媒に比べて、150 mV小さい過電圧で3.5倍の反応速度を達成した。水溶性の向上を目指し、bpy上にカルボキシ基を導入した水溶性錯体触媒を合成した。10%のトルフルオロエタノールと水の混合溶液中でのCVから、[Ru(OH2)(bpy)(thaq)]2+と同等の触媒活性を示すことがわかった。また、ESR測定により重要な中間体であるフェノキシルラジカル種の生成を確認した。

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    • 光合成酸素発生中心の機能を模倣した二核ルテニウム錯体による水の酸化反応

      日本学術振興会  科学研究費助成事業 新学術領域研究(研究領域提案型) 

      和田 亨

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      4 2015 - 3 2017

      Grant number:15H00884

      Grant amount:\3900000 ( Direct Cost: \3000000 、 Indirect Cost:\900000 )

      本研究課題では人工光合成のボトルネックといわれる水の四電子酸化反応を、平衡電極電位(+1.23 V vs.NHE, pH0)よりも+100mVから+200 mV程度の過電圧で進行させる小過電圧触媒系の実現を目指し、光合成の仕組みを模倣した人工系二核ルテニウム錯体触媒の開発を行った。天然の光合成では、酸素発生中心であるマンガンクラスターの近傍に存在するチロシン残基が電子とプロトンの移動に重要な役割を担っている。本研究ではOECを模倣して、チロシンと同じフェノール骨格を分子内に有する二核ルテニウム錯体の合成について検討した。当初は架橋部位をアントラセノールとした二核化配位子の合成を目指し、多くの合成経路について検討したが、実用的な収率に至らなかった。そこで、アントラセンの1位にルテニウムを結合するターピリジル基、8位にヒドロキシフェニル基を有する配位子の合成を検討した。最終的に、アントラセン-1,8-ジボロン酸とトリフルオロメタンスルホニルターピリジン及びブロモアニソールのワンポット鈴木ー宮浦クロスカップリング反応で良好な収率で合成に成功した。この配位子を用いて単核ルテニウム錯体を合成し、その構造を単結晶X-線構造解析で明らかにした。さらに合成した錯体のCVを測定し、水の酸化に対して触媒活性を示すことがわかった。有機溶媒中ではフェノール部位の不可逆な酸化波が+1.2V(vs. SCE)に観測され、水中ではこの電位近辺から水の酸化に由来する触媒電流が生じた。現在、フェノール部位が水の酸化に与える影響と反応機構について検討を行っている。さらに、非常に強い電子供与性の配位子を有するルテニウム錯体が、小過電圧で水の酸化を触媒することを明らかにした。二核ルテニウム錯体触媒に夜水の酸化反応については、反応活性種が[Ru(IV)=O O=Ru(V)]である明確な証拠を得た。

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    • 光合成酸素発生中心の仕組みを組み込んだ複核ルテニウム錯体による水の酸化反応

      日本学術振興会  科学研究費助成事業 新学術領域研究(研究領域提案型) 

      和田 亨

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      4 2013 - 3 2015

      Grant number:25107524

      Grant amount:\3640000 ( Direct Cost: \2800000 、 Indirect Cost:\840000 )

      光合成酸素発生中心(Oxygen evolving center, OEC)では、水の酸化による酸素発生反応を触媒するマンガンクラスターに水素結合したチロシン残基が存在しており、電子とプロトンの伝達に重要な役割をしている。本研究では、すでに研究代表者らが開発している二核ルテニウム構造を有する水の酸化触媒に、チロシン残基を模倣した酸化還元活性な架橋配位子を導入することより、より高活性な水の酸化触媒系を構築することを目的とする。
      酸化還元活性な架橋配位子として二つのターピリジンをアントラセノールでつないだ新規配位子、ビス(ターピリジル)アントラセノールの合成について検討した。1,8-ジクロロアントラキノンから4段階の反応を経て合成が可能であることを明らかにした。収率の向上にむけて検討を継続している。また、別途に新規架橋配位子ビス(ターピリジル)アントラキノン(btpyaq)を用いた二核ルテニウム錯体を合成した。このアントラキノン架橋錯体を触媒に用いると、対応するアントラセン架橋錯体を触媒に用いたときに比べ、水の酸化の反応速度が向上することが明らかとなった。この結果は、架橋部位のアントラキノンのカルボニル基が親水性基として働き、酸素分子と水分子の置換反応が促進されたためだと考えられる。また、電子供与性が非常に強い配位子であるジピリジルフェニル基を有する単核ルテニウム錯体を合成したところ、対応するターピリジン錯体と比較して720mVもの酸化還元電位の負電位シフトが観測された。穏やかな酸化剤である[Ru(bpy)3]3+ (bpy = ビピリジン)を用いて水の酸化反応を行ったところ酸素発生が確認された。これらの結果より触媒設計に於いて、電位を低下し反応速度を向上させるための要素を明らかにすることが出来た。

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    • Developments of Oxygen Evolving Complex Catalysts Aiming for Energy Conversion

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

      WADA Tohru

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      2011 - 2013

      Grant number:23550084

      Grant amount:\5330000 ( Direct Cost: \4100000 、 Indirect Cost:\1230000 )

      Four-electron water oxidation is a necessary for realization of artificial photosynthesis. In this research, we developed mono- and binuclear complex catalysts for the purpose of four-electron water oxidation near the equilibrium potential. We have synthesized the mono-ruthenium complexes having a strong electron donor ligand, such as tetramethylethylenediamine (tmen) or dipyridylbenzene (dpb). These mono-ruthenium complexes have been oxidized at lower potential compared with that of the corresponding ruthenium complex having the electron acceptor ligand. In fact, these complexes have catalyzed water oxidation in the presence of [Ru(boy)]3+ (bpy = bipyridine) as an oxidant. Furthermore, we synthesized dinuclear ruthenium complex with a phosphate group in order to develop the hybrid catalyst of metal-oxide and metal complex. Electrochemical measurements have revealed that the dinuclear ruthenium complex modified on ITO electrode shows reversible redox reaction.

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    • Development of Highly Active Catalyst for Oxygen Evolution

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

      WADA Tohru

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      2008 - 2009

      Grant number:20750123

      Grant amount:\4420000 ( Direct Cost: \3400000 、 Indirect Cost:\1020000 )

      There is much attention to water-oxidation catalyst from a view point of environmental and energy problems. In this project, dinuclear ruthenium complex was prepared as a water oxidation catalyst. The mechanism of O-O bond formation from two water molecules was elucidated by a spectroscopic analysis.

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    • エネルギー変換を指向した水およびアンモニアの酸化的活性化触媒の開発

      日本学術振興会  科学研究費助成事業 特定領域研究 

      和田 亨

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      2007 - 2007

      Grant number:19028064

      Grant amount:\2000000 ( Direct Cost: \2000000 )

      遷移金属錯体に配位したラジカル種は生体内の酵素反応の活性中心にみられ、その反応性に注目が集まっている。我々はこれまでにRu^<III>(3,5-t-Bu_2sq)(3,5-t-Bu_2sq=3,5-ジ-tert-ブチル-1,2-ベンゾセミキノン)骨格上に配位した水分子がプロトンを解離することにより、容易にオキソ配位子上に不対電子を誘起したオキシルラジカル錯体[Ru^<II>(O^<-.>)(3,5-t-Bu_2sq)(terpy)]を生成することを報告している。今回、同様のRu^<III>(3,5-t-Bu_2sq)骨格に四座配位子NH_2-bpa(NH_2-bpa=ビス(2-ピリジルメチル)-2-アミノエチルアニリン)を導入することにより、安定なアニリノラジカル錯体の合成と同定に成功した。[Ru^<III>(NH-bpa)(3,5-t-Bu_2sq)]^+は872nmと1172nmに特徴的な吸収を示すが、これらはそれぞれルテニウム-セミキノン間、ルテニウム-アニリド間のMLCTに帰属される。ジメトキシエタン中、[Ru^<III>(NH-bpa)(3,5-t-Bu_2sq)]^+に対して1等量のt-BuOKを作用させるとアニリドプロトンが解離しアニリノラジカル錯体[Ru^<III>(^-N-bpa)(3,5-t-Bu_2sq)]^0を生成する。[Ru^<III>(^-N-bpa)(3,5-t-Bu_2sq)]^0のEPRを測定するとΔM_s=2の遷移基づくシグナルがg=4.2に観測されたことから、S=1の三重項状態であることが分かった。さらに[Ru^<III>(^-N-bpa)(3,5-t-Bu_2sq)]^0を電気化学的に一電子還元することにより生成した[Ru^<III>(^-N-bpa)(3,5-t-Bu_2cat)]^<-1>(cat=カテコール)のEPRシグナルには、N原子のハイパーファインカップリングが観測された。セミキノン-アニリノラジカル錯体[Ru^<III>(^-N-bpa)(3,5-t-Bu_2sq)]^0とカテコラト-アニリノラジカル錯体[Ru^<III>(^-N-bpa)(3,5-t-Bu_2cat)]^<-1>に対してDFT計算を行うと、前者では電子スピンが非局在化しているのに対して、後者ではN-bpa上にほぼ局在化していることが分かった。これまでにアニリノラジカル錯体の報告はあるが、いずれも酸化剤を用いているのに対して、本反応系では酸塩基平衡のみを駆動力としてラジカル種を誘起している。この様な穏和な条件でのラジカル生成は酵素活性中心の機能解明のみならず、新たな触媒反応への展開が可能である。

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    • 可視光エネルギーを利用した水の酸化触媒の開発

      日本学術振興会  科学研究費助成事業 若手研究(B) 

      和田 亨

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      2006 - 2007

      Grant number:18750126

      Grant amount:\3500000 ( Direct Cost: \3500000 )

      二核化配位子1,8-ビス(ターピリジル)アントラセン(btpyan)を用いて、(3,6-t-Bu_2q)Ru(OH)(3,6-t-Bu_2q=3,6-ジ-tert-ブチル-1,2-ベンゾキノン)部位を向かい合わせに架橋した[Ru_2(OH)_2(3,6-t-Bu_2q)_2(btpyan)](SbF_6)_2は水の四電子酸化による酸素発生反応を効率よく触媒する。ジオキソレン配位子上の置換基は触媒活性に大きく影響し、3,6-t-Bu基の代わりに4-NO_2,3,5-Cl_2が置換した錯体では酸素発生反応に対する触媒活性を示さなかった。そこで、錯体の電子状態に対するジオキソレン配位子上の置換基効果を明らかにするため、一連の[Ru(OAc)(L)(terpy)]錯体(L=3,5-t-Bu_2C_6H_2O_2,4-t-BuC_6H_3O_2,4-ClC_6H_3O_2,3,5-Cl_2C_6H_2O_2,Cl_4C_6O_2,terpy=2,2':6',2"-ターピリジン)を合成し、その電子状態をEPRで検討したところRu(L)部位はRu^<II>(sq)(sq=semiquinone)とRu^<III>(cat)(cat=catecholato)の中間的な電子状態をとり、置換基の電子供与性が増加するほどRu^<II>(sq)に、電子吸引性が大きいほどRu^<III>(cat)に近いことが明らかになった。DFT計算を用いて、酸素発生反応の機構に関して検討を行ったところ、[Ru_2(OH)_2(3,6-t-Bu_2q)_2(btpyan)]^<2+>は二つのプロトンを解離することにより分子内でラジカル的にO-O結合を形成することが示唆された。また興味深いことに、酸素発生に必要な四電子の酸化を錯体内の中心金属であるルテニウムではなく、ジオキソレン配位子が担っていることが分かった。これらの結果はこれまでに提唱されていない全く新しい酸素発生機構であり、同研究領域に大きな影響を与えるものと考えられる。

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    Industrial property rights

    • 金属錯体およびこれを含む燃料電池用カソード

      和田亨

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      Application no:特願2013-121811  Date applied:10 6 2013

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    • Ruthenium(III) Ammine Complexes

      Takami Hino, Tohru Wada, Koji Tanaka

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      Announcement no:4212411  Date announced:7 11 2008

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    Academic Activities

    • Consortium of All Nippon Artificial Photosynthesis Project for Living Earth (CanApple)

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      Type:Other 

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    Social Contribution

    • 化学の未来を創る女子中高生のチャレンジラボ

      Lecturer, Planner

      1 6 2018 - 31 3 2020

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      Type:Visiting lecture

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