Turning photocatalytic H2 evolution into CO2 reduction of molecular nickel(II) complexes by using a redox–active bipyridine ligand

Abstract

Two bis–NHC (NHC = N–heterocyclic carbene) Ni(II) complexes has been designed and synthesized as molecular catalysts in photocatalytic H2 evolution and CO2 reduction. The Ni(II) complex with a redox–innocent 1,2–bis(diphenylphosphaneyl)ethane ligand only generates H2 with a TON of 149 ± 5 and no product of CO2 reduction is found, while the other Ni(II) complex with a redox–active 4,4′–dimethyl–2,2′–bipyridine ligand can catalyze reduction of CO2 to CO with a TON of 41 ± 2 and 93.2% selectivity over H2 evolution. This finding shows a redox–active ligand is capable of boosting CO2 photoreduction of a molecular metal complex, which is helpful for designing molecular catalysts in CO2 photoreduction.