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Mechanism of Water Oxidation Catalyzed by a Dinuclear Ruthenium Complex Bridged by Anthraquinone

Department of Chemistry, College of Science and Research Center for Smart Molecules, Rikkyo University, 3-34-1, Nishi-Ikebukuro, Toshima-ku, Tokyo 171-8501, Japan
School of Science and Engineering, Tokyo Denki University, Hatoyama, Hiki-gun, Saitama 350-0394, Japan
Author to whom correspondence should be addressed.
Catalysts 2017, 7(2), 56;
Received: 5 January 2017 / Revised: 2 February 2017 / Accepted: 6 February 2017 / Published: 10 February 2017
(This article belongs to the Special Issue Water Oxidation Catalysis)
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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 [Ru2(µ-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 E1/2 = +0.62, +0.82 V, and Epa = +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+. View Full-Text
Keywords: water oxidation; Ruthenium complex; mechanism; Raman spectroscopy; electrochemistry water oxidation; Ruthenium complex; mechanism; Raman spectroscopy; electrochemistry

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Wada, T.; Nishimura, S.; Mochizuki, T.; Ando, T.; Miyazato, Y. Mechanism of Water Oxidation Catalyzed by a Dinuclear Ruthenium Complex Bridged by Anthraquinone. Catalysts 2017, 7, 56.

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