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

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

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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(PPh 3)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 [RuIII 2(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 [RuII 2(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 [RuIII 2(OH)2(cat)2(btpyan)]0.

Original languageEnglish
Pages (from-to)2225-2233
Number of pages9
JournalDalton Transactions
Volume40
Issue number10
DOIs
Publication statusPublished - Mar 14 2011

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ASJC Scopus subject areas

  • Inorganic Chemistry

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