Nakada Akinobu, Koike Kazuhide, Nakashima Takuya, Morimoto Tatsuki, Ishitani Osamu
Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology , 2-12-1-NE-1 O-okayama, Meguro-ku, Tokyo 152-8550, Japan.
Inorg Chem. 2015 Feb 16;54(4):1800-7. doi: 10.1021/ic502707t. Epub 2015 Feb 5.
In an aqueous solution, photophysical, photochemical, and photocatalytic abilities of a Ru(II)-Re(I) binuclear complex (RuReCl), of which Ru(II) photosensitizer and Re(I) catalyst units were connected with a bridging ligand, have been investigated in details. RuReCl could photocatalyze CO2 reduction using ascorbate as an electron donor, even in an aqueous solution. The main product of the photocatalytic reaction was formic acid in the aqueous solution; this is very different in product distribution from that in a dimethylformamide (DMF) and triethanolamine (TEOA) mixed solution in which the main product was CO. A (13)CO2 labeling experiment clearly showed that formic acid was produced from CO2. The turnover number and selectivity of the formic acid production were 25 and 83%, respectively. The quantum yield of the formic acid formation was 0.2%, which was much lower, compared to that in the DMF-TEOA mixed solution. Detail studies of the photochemical electron-transfer process showed back-electron transfer from the one-electron-reduced species (OERS) of the photosensitizer unit to an oxidized ascorbate efficiently proceeded, and this should be one of the main reasons why the photocatalytic efficiency was lower in the aqueous solution. In the aqueous solution, ligand substitution of the Ru(II) photosensitizer unit proceeded during the photocatalytic reaction, which was a main deactivation process of the photocatalytic reaction. The product of the ligand substitution was a Ru(II) bisdiimine complex or complexes with ascorbate as a ligand or ligands.
在水溶液中，已详细研究了一种钌（II）-铼（I）双核配合物（RuReCl）的光物理、光化学和光催化能力，其中钌（II）光敏剂单元和铼（I）催化剂单元通过桥连配体相连。即使在水溶液中，RuReCl也能以抗坏血酸作为电子供体光催化二氧化碳还原。光催化反应的主要产物在水溶液中是甲酸；这在产物分布上与二甲基甲酰胺（DMF）和三乙醇胺（TEOA）混合溶液中的情况非常不同，在后者中主要产物是一氧化碳。一项¹³CO₂标记实验清楚地表明甲酸是由二氧化碳产生的。甲酸生成的周转数和选择性分别为25和83%。甲酸形成的量子产率为0.2%，与DMF-TEOA混合溶液中的相比要低得多。对光化学电子转移过程的详细研究表明，从光敏剂单元的单电子还原物种（OERS）到氧化的抗坏血酸的反向电子转移有效地进行，这应该是水溶液中光催化效率较低的主要原因之一。在水溶液中，光催化反应过程中钌（II）光敏剂单元发生配体取代，这是光催化反应的主要失活过程。配体取代的产物是一种钌（II）双二亚胺配合物或与抗坏血酸作为配体的配合物。
