Exploring the effect of axial ligand substitution (X = Br, NCS, CN) on the photodecomposition and electrochemical activity of [MnX(N–C)(CO)3] complexes

Abstract

Four new Mn( i)-NHC compounds are tested for light stability and catalytic efficiency for reducing CO ₂ to CO.

Abstract

The synthesis, electrochemical activity, and relative photodecomposition rate is reported for four new Mn( i) N-heterocyclic carbene complexes: [MnX( N-ethyl- N′-2-pyridylimidazol-2-ylidine)(CO) ₃] (X = Br, NCS, CN) and [MnCN( N-ethyl- N′-2-pyridylbenzimidazol-2-ylidine)(CO) ₃]. All compounds display an electrocatalytic current enhancement under CO ₂ at the potential of the first reduction, which ranges from −1.53 V to −1.96 V versus the saturated calomel electrode. Catalytic CO production is observed for all species during four-hour preparative-scale electrolysis, but substantial H ₂ is detected in compounds where X is not Br. All species eventually decompose under both 350 nm and 420 nm light, but cyanide substituted complexes (X = CN) last significantly longer (up to 5×) under 420 nm light as a result of a blue-shifted MLCT band.