Catalytic Water Oxidation by Mononuclear Ru Complexes with an Anionic Ancillary Ligand

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• 作者：Lianpeng Tong ; A. Ken Inge ; Lele Duan ; Lei Wang ; Xiaodong Zou ; Licheng Sun
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：March 4, 2013
• 年：2013
• 卷：52
• 期：5
• 页码：2505-2518
• 全文大小：660K
• 年卷期：v.52,no.5(March 4, 2013)
• ISSN：1520-510X

文摘

Mononuclear Ru-based water oxidation catalysts containing anionic ancillary ligands have shown promising catalytic efficiency and intriguing properties. However, their insolubility in water restricts a detailed mechanism investigation. In order to overcome this disadvantage, complexes [Ru^II(bpc)(bpy)OH₂]⁺ (1⁺, bpc = 2,2鈥?bipyridine-6-carboxylate, bpy = 2,2鈥?bipyridine) and [Ru^II(bpc)(pic)₃]⁺ (2⁺, pic = 4-picoline) were prepared and fully characterized, which features an anionic tridentate ligand and has enough solubility for spectroscopic study in water. Using Ce^IV as an electron acceptor, both complexes are able to catalyze O₂-evolving reaction with an impressive rate constant. On the basis of the electrochemical and kinetic studies, a water nucleophilic attack pathway was proposed as the dominant catalytic cycle of the catalytic water oxidation by 1⁺, within which several intermediates were detected by MS. Meanwhile, an auxiliary pathway that is related to the concentration of Ce^IV was also revealed. The effect of anionic ligand regarding catalytic water oxidation was discussed explicitly in comparison with previously reported mononuclear Ru catalysts carrying neutral tridentate ligands, for example, 2,2鈥?6鈥?2鈥?terpyridine (tpy). When 2⁺ was oxidized to the trivalent state, one of its picoline ligands dissociated from the Ru center. The rate constant of picoline dissociation was evaluated from time-resolved UV鈥搗is spectra.