Department of Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan.
J Am Chem Soc. 2011 Aug 3;133(30):11605-13. doi: 10.1021/ja2024965. Epub 2011 Jul 7.
Catalytic water oxidation to generate oxygen was achieved using all-inorganic mononuclear ruthenium complexes bearing Keggin-type lacunary heteropolytungstate, Ru(III)(H(2)O)SiW(11)O(39) (1) and Ru(III)(H(2)O)GeW(11)O(39) (2), as catalysts with (NH(4))(2)[Ce(IV)(NO(3))(6)] (CAN) as a one-electron oxidant in water. The oxygen atoms of evolved oxygen come from water as confirmed by isotope-labeled experiments. Cyclic voltammetric measurements of 1 and 2 at various pH's indicate that both complexes 1 and 2 exhibit three one-electron redox couples based on ruthenium center. The Pourbaix diagrams (plots of E(1/2) vs pH) support that the Ru(III) complexes are oxidized to the Ru(V)-oxo complexes with CAN. The Ru(V)-oxo complex derived from 1 was detected by UV-visible absorption, EPR, and resonance Raman measurements in situ as an active species during the water oxidation reaction. This indicates that the Ru(V)-oxo complex is involved in the rate-determining step of the catalytic cycle of water oxidation. The overall catalytic mechanism of water oxidation was revealed on the basis of the kinetic analysis and detection of the catalytic intermediates. Complex 2 exhibited a higher catalytic reactivity for the water oxidation with CAN than did complex 1.
使用负载 Keggin 型缺杂多钨酸盐的全无机单核钌配合物Ru(III)(H(2)O)SiW(11)O(39)（1）和Ru(III)(H(2)O)GeW(11)O(39)（2）作为催化剂，在水中以（NH(4))(2)[Ce(IV)(NO(3))(6)]（CAN）作为单电子氧化剂，实现了水的催化氧化生成氧气。通过同位素标记实验证实，生成氧气中的氧原子来自水。在不同 pH 值下对 1 和 2 的循环伏安测量表明，两种配合物 1 和 2 均基于钌中心表现出三个单电子氧化还原偶对。Pourbaix 图（E(1/2)与 pH 的关系图）表明，Ru(III)配合物与 CAN 被氧化为 Ru(V)-氧配合物。在水氧化反应过程中，通过 UV-可见吸收、EPR 和共振拉曼原位测量检测到来自 1 的 Ru(V)-氧配合物作为活性物种。这表明 Ru(V)-氧配合物参与了水氧化催化循环的速率决定步骤。基于动力学分析和催化中间体的检测，揭示了水氧化的总体催化机制。与 1 相比，配合物 2 对 CAN 催化水氧化具有更高的反应活性。
