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Issue 10, 2011
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Substituents dependent capability of bis(ruthenium-dioxolene-terpyridine) complexes toward water oxidation

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Abstract

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, [Ru2(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 [RuII2(OH)2(sq)2(btpyan)]0 (sq = semiquinonato). On the other hand, the electronic states of [2]0 and [3]0 are close to [RuIII2(OH)2 (cat)2(btpyan)]0 (cat = catecholato), indicating that a dioxolene having electron-withdrawing groups stabilizes [RuIII2(OH)2(cat)2(btpyan)]0 rather than [RuII2(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 O2 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 [RuII2(OH)2(sq)2(btpyan)]0 and [RuIII2(OH)2(cat)2(btpyan)]0.

Graphical abstract: Substituents dependent capability of bis(ruthenium-dioxolene-terpyridine) complexes toward water oxidation

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Supplementary files

Article information


Submitted
06 Aug 2010
Accepted
01 Oct 2010
First published
23 Dec 2010

Dalton Trans., 2011,40, 2225-2233
Article type
Paper

Substituents dependent capability of bis(ruthenium-dioxolene-terpyridine) complexes toward water oxidation

T. Wada, J. T. Muckerman, E. Fujita and K. Tanaka, Dalton Trans., 2011, 40, 2225
DOI: 10.1039/C0DT00977F

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