Study of Re(I) Carbene Complexes for Photocatalytic Reduction of Carbon Dioxide

A series of carbene-containing dicarbonyl Re(I) bipyridyl complexes with metal-to-ligand charge transfer (MLCT) transitions in the visible region have been synthesized. Most of these complexes are highly selective and efficient photocatalysts capable of using visible light for CO2 reduction to CO. The activities of single- and two-component photocatalytic systems based on a series of carbene-containing dicarbonyl Re(I) bipyridyl complexes as photocatalysts and photosensitizers have been investigated. Importantly, the CO yields and turnover numbers (TONs) can be further enhanced significantly in the two-component photocatalytic systems. A detailed study suggests that the deactivations of these photocatalyses arise from the photo-degradation of the photosensitizers or photocatalysts. The results suggest that efficient and robust rhenium-based two-component photocatalytic systems can be developed by combining an active rhenium(I) catalyst, which does not strongly absorb the excitation light, for activating CO2 together with a highly photostable photosensitizer with strong absorptivity for harvesting excitation light.