Electrochemical CO₂ Reduction at Glassy Carbon Electrodes Functionalized by Mn^I and Re^I Organometallic Complexes

The catalytic activities towards electrochemical CO₂ reduction of two new rhenium and manganese complexes, namely fac-Mn(apbpy)(CO)₃Br (1) and fac-Re(apbpy)(CO)₃Cl (2) (apbpy=4-(4-aminophenyl)-2,2′-bipyridine), in both homogeneous and heterogeneous phases are compared. A glassy carbon electrode (GCE) surface has been functionalized with complexes 1 and 2 by two approaches: a) direct electrochemical oxidation of the amino group with formation of C−N bonds, and b) electrochemical reduction of the corresponding diazonium salts with formation of C−C bonds. The chemically modified GCEs show efficient conversion of CO₂ into CO, with turnover numbers (TONs) about 60 times higher than those of the corresponding catalysts in homogeneous solutions, and in a much shorter time.