Photochemical and electrochemical catalytic reduction of CO2 with NHC-containing dicarbonyl rhenium(I) bipyridine complexes

The electrochemical and photochemical catalytic reductions of CO2 using N,O and N,S-NHC-containing dicarbonyl rhenium(I) bipyridine complexes have been investigated. By replacing the carbonyl ligand in tricarbonyl rhenium(I) complexes with a weaker p-accepting ligand, the characteristic MLCT transitions shifted to lower energy. This makes photocatalysts capable of harvesting low-energy visible light for catalyzing CO2 reduction. A detailed study revealed that these dicarbonyl rhenium(I) complexes are also highly selective for photocatalysis of CO2 to CO with a good quantum efficiency (10%), similar to that of the tricarbonyl rhenium(I) complex analogues. From the electrochemical study, it was observed that the catalysts efficiently produce CO from CO2 with high turnover frequency and good stability over time.