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 photodegradation 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.