配体取代基对三羰基铼配合物光催化还原CO_2的影响  

Ligand Substituent Effects on Rhenium Tricarbonyl Catalysts in CO_2 Reduction

作　　者：陈金平[1] 都新丰[1] 于天君[1] 曾毅[1] 张小辉[1] 李嫕[1] 

机构地区：[1]中国科学院理化技术研究所光化学转换与功能材料重点实验室,北京100190

出　　处：《化学学报》2016年第6期523-528,共6页Acta Chimica Sinica

基　　金：国家自然科学基金(Nos.21472201;21573266;21233011);科技部973计划项目(Nos.2013CB834700;2013CB834505)资助~~

摘　　要：设计并合成了四种联吡啶配体上共价修饰不同取代基的三羰基铼配合物fac-Re(L)(CO)_3Cl:即取代基分别为甲基(Re-Me)、羧基(Re-Ac)、季铵盐(Re-Qa)以及咪唑盐(Re-Im)的铼配合物,化合物的结构均经过核磁氢谱、质谱以及红外光谱的确认,测定了四种配合物第一和第二还原电位.分别以该系列铼配合物为催化剂和光敏剂、三乙醇胺为电子牺牲体构建了均相可见光催化还原CO_2体系,配体上取代基对催化剂的催化效果有显著的影响,催化活性Re-Qa>Re-Ac≈Re-Me>Re-Im.不同实验条件下四种催化剂的吸收光谱随时间变化研究表明,铼配合物的催化效果和其在催化过程中的失活速率密切相关,其变化趋势与催化剂失活速率一致,催化剂的失活发生在催化剂得到一个电子后的单电子还原态中间体(One-electron reduced species,OER).瞬态吸收光谱检测到了催化过程中的OER的生成,证实光催化还原CO_2过程通过生成OER中间体进行的.The Re （I） complexes originally reported by Lehn et al. is one of the most important catalysts used for photocatalytical reduction of CO2 in homogeneous system. The mechanism for the photocatalytic reduction of CO2 to CO with Re （I） complexes has been thoroughly investigated recently. In this study, a series of rhenium tricarbonyl catalysts （Re-Me, Re-Ac, Re-Qa and Re-Im） with different substituents on 2,2-bipyridine ligand were synthesized and characterized. These catalysts were successfully applied to a light induced CO2 reduction system with triethanolamine （TEOA） as sacrificial reagent, exhib- iting different turnover numbers for different catalysts. The highest turnover number was achieved for the catalyst of Re-Qa, and Re-Me and Re-Ac exhibit similar activity, while Re-Im exhibits almost no activity in the photocatalytic conversion of CO2 to CO. UV-vis spectra show that the rate of deactivation is linked to the decomposition of the catalysts in the photocatalytic system. No decomposition was observed in the absence of TEOA, suggesting that the deactivation occurs via the intermediate of one-electron-reduced （OER） species. The transient absorption spectra conformed the formation of OER in the catalytic system. The reasons for the highest turnover number of Re-Qa may be attributed to the quaternary ammonium salt group, which can serve as a mediator to facilitate the reduction process. While in the case of Re-Im, the imidazolium group might accelerate the deactivation of OER species by an intramolecular interaction. Further experiments on this effect are the subject of ongoing investigations.

关 键 词：均相光催化 CO2还原 铼配合物 取代基效应 催化失活 

分 类 号：O643.36[理学—物理化学]