Takeda Hiroyuki, Koike Kazuhide, Inoue Haruo, Ishitani Osamu
Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1-E1-9 O-okayama, Meguro-ku, Tokyo, 152-8551, Japan.
J Am Chem Soc. 2008 Feb 13;130(6):2023-31. doi: 10.1021/ja077752e. Epub 2008 Jan 19.
The reaction mechanism of photocatalytic CO2 reduction using rhenium(I) complexes has been investigated by means of a detailed comparison of the photocatalyses of three rhenium(I) complexes, fac-[Re(bpy)(CO)3L] (L = SCN- (1-NCS), Cl- (1-Cl), and CN- (1-CN)). The corresponding one-electron-reduced species (OER) of the complexes play two important roles in the reaction: (a) capturing CO2 after loss of the monodentate ligand (L) and (b) donation of the second electron to CO2 by another OER without loss of L. In the case of 1-NCS, the corresponding OER has both of the capabilities in the photocatalytic reaction, resulting in more efficient CO formation (with a quantum yield of 0.30) than that of 1-Cl (quantum yield of 0.16), for which OER species have too short a lifetime to accumulate during the photocatalytic reaction. On the other hand, 1-CN showed no photocatalytic ability, because the corresponding OER species does not dissociate the CN- ligand. Based on this mechanistic information, the most efficient photocatalytic system was successfully developed using a mixed system with fac-[Re(bpy)(CO)3(CH3CN)]+ and fac-[Re{4,4'-(MeO)2bpy}(CO)3{P(OEt)3}]+, for which the optimized quantum yield for CO formation was 0.59.
通过对三种铼（I）配合物fac-[Re(bpy)(CO)3L]（L = SCN- (1-NCS)、Cl- (1-Cl) 和 CN- (1-CN)）的光催化反应进行详细比较，研究了使用铼（I）配合物光催化还原二氧化碳的反应机理。这些配合物相应的单电子还原物种（OER）在反应中发挥两个重要作用：（a）在单齿配体（L）失去后捕获二氧化碳，以及（b）另一个OER在不失去L的情况下将第二个电子给予二氧化碳。对于1-NCS，相应的OER在光催化反应中具备这两种能力，导致生成一氧化碳的效率更高（量子产率为0.30），高于1-Cl（量子产率为0.16），1-Cl的OER物种寿命太短，无法在光催化反应过程中积累。另一方面，1-CN没有显示出光催化能力，因为相应的OER物种不会使CN-配体解离。基于这一机理信息，使用fac-[Re(bpy)(CO)3(CH3CN)]+和fac-[Re{4,4'-(MeO)2bpy}(CO)3{P(OEt)3}]+的混合体系成功开发出了最有效的光催化体系，其生成一氧化碳的优化量子产率为0.59。
