Visible-Light-Driven Carbon Dioxide Reduction Catalyzed by Iron Schiff-Base Complexes

Light-dependent reduction of carbon dioxide (CO₂) can be developed using nonexpensive and abundant molecular catalysts and inorganic photosensitizers based on nonnoble metals. The photoreduction of CO₂ catalyzed by a series of 11 metal-salophen complexes, based on variously functionalized salophen ligands, has been investigated using a Cu-based photosensitizer, [Cu^I(bathocupoine)(xantphos)], for light harvesting. This provides one of the currently few fully earth-abundant systems for efficient CO₂ reduction driven by visible light. Using 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) as the sacrificial reductant in acetonitrile/triethanolamine solution, a maximum turnover number for CO production of 900–1600, a maximum initial turnover frequency of 1300–1700 h^–1 with 93–96% CO/H₂ selectivity, and a high quantum yield of 12–15% (at 420 nm) were achieved with Fe-based complexes. Thorough photophysical studies coupled to DFT calculations allowed tracking of reaction intermediates and provided insights into the reaction mechanism.