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

Abstract

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 π-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.