New Water Oxidation Chemistry of a Seven-Coordinate Ruthenium Complex with a Tetradentate Polypyridyl Ligand

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• 作者：James T. Muckerman ; Marta Kowalczyk ; Yosra M. Badiei ; Dmitry E. Polyansky ; Javier J. Concepcion ; Ruifa Zong ; Randolph P. Thummel ; Etsuko Fujita
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：July 7, 2014
• 年：2014
• 卷：53
• 期：13
• 页码：6904-6913
• 全文大小：414K
• ISSN：1520-510X

文摘

The mononuclear ruthenium(II) complex [Ru]²⁺ (Ru = Ru(dpp)(pic)₂, where dpp is the tetradentate 2,9-dipyrid-2鈥?yl-1,10-phenanthroline ligand and pic is 4-picoline) reported by Thummel鈥檚 group (Inorg. Chem. 2008, 47, 1835鈥?848) that contains no water molecule in its primary coordination shell is evaluated as a catalyst for water oxidation in artificial photosynthesis. A detailed theoretical characterization of the energetics, thermochemistry, and spectroscopic properties of intermediates allowed us to interpret new electrochemical and spectroscopic experimental data, and propose a mechanism for the water oxidation process that involves an unprecedented sequence of seven-coordinate ruthenium complexes as intermediates. This analysis provides insights into a mechanism that generates four electrons and four protons in the solution and a gas-phase oxygen molecule at different pH values. On the basis of the calculations and corroborated substantially by experiments, the catalytic cycle goes through [²Ru^III]³⁺ and [²Ru^V(O)]³⁺ to [¹Ru^IV(OOH)]³⁺ then [²Ru^III(路路路³O₂)]³⁺ at pH 0, and through [³Ru^IV(O)]²⁺, [²Ru^V(O)]³⁺, and [¹Ru^IV(OO)]²⁺ at pH 9 before reaching the same [²Ru^III(路路路³O₂)]³⁺ species, from which the liberation of the weakly bound O₂ might require an additional oxidation to form [³Ru^IV(O)]²⁺ to initiate further cycles involving all seven-coordinate species.