Redox Mediator Effect on Water Oxidation in a Ruthenium-Based Chromophore鈥揅atalyst Assembly

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• 作者：Michael R. Norris ; Javier J. Concepcion ; Daniel P. Harrison ; Robert A. Binstead ; Dennis L. Ashford ; Zhen Fang ; Joseph L. Templeton ; Thomas J. Meyer
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：February 13, 2013
• 年：2013
• 卷：135
• 期：6
• 页码：2080-2083
• 全文大小：278K
• 年卷期：v.135,no.6(February 13, 2013)
• ISSN：1520-5126

文摘

The synthesis, characterization, and redox properties are described for a new ruthenium-based chromophore鈥揷atalyst assembly, [(bpy)₂Ru(4-Mebpy-4鈥?bimpy)Ru(tpy)(OH₂)]⁴⁺ (1, [Ru_a^II-Ru_b^II-OH₂]⁴⁺; bpy = 2,2鈥?bipyridine; 4-Mebpy-4鈥?bimpy = 4-(methylbipyridin-4鈥?yl)-N-benzimid-N鈥?pyridine; tpy = 2,2鈥?6鈥?2鈥?terpyridine), as its chloride salt. The assembly incorporates both a visible light absorber and a catalyst for water oxidation. With added ceric ammonium nitrate (Ce^IV, or CAN), both 1 and 2, [Ru(tpy)(Mebim-py)(OH₂)]²⁺ (Mebim-py = 2-pyridyl-N-methylbenzimidazole), catalyze water oxidation. Time-dependent UV/vis spectral monitoring following addition of 30 equiv of Ce^IV reveals that the rate of Ce^IV consumption is first order both in Ce^IV and in an oxidized form of the assembly. The rate-limiting step appears to arise from slow oxidation of this intermediate followed by rapid release of O₂. This is similar to isolated catalyst 2, with redox potentials comparable to the [-Ru_b-OH₂]²⁺ site in 1, but 1 is more reactive than 2 by a factor of 8 due to a redox mediator effect.