Product Control in Visible-Light-Driven CO₂ Reduction by Switching Metal Centers of Binuclear Catalysts

Controlled selectivity of products for visible-light-driven photocatalytic reduction of CO2 in water-containing systems is highly desirable. Here, we report two highly efficient and selective binuclear complex catalysts, [Co2(MeL-S)(OAc)2](OAc) (CoCo) and [Cu2(MeL-S)(H2O)](CF3SO3)2·2H2O (CuCu), bearing a N6S-type polypyridine sulfur ligand (MeL-S–) in situ formed from 2,6-bis[(bis(pyridylmethyl)amino)methyl]-4-methylmercaptophenylsulfide (MeL-S-S-LMe), which can promote the selective reduction of CO2 into CO and HCOOH employing [Ru(phen)3](PF6)2 as photosensitizer, respectively, under the irradiation of visible light in CH3CN/H2O (4/1 v/v) solution. We found that CoCo can catalyze the conversion of CO2 to CO with a high selectivity (96%) and a TON value of 6188. However, HCOOH was found for the CuCu case with a high selectivity (98%) and TON value (7540). Experimental results and DFT calculations revealed that the close Cu···Cu distance in CuCu facilitates the hydrogenation process through a 3-center-4-electron (3c-4e–) bond to give high efficiency and high HCOOH selectivity. However, 3c-4e– is absent in CoCo due to the well-separated Co centers and high total valence of the Co atoms, which lead to a high CO selectivity.