Cooperation of Two Metal Centers in a CO 2 Electroreduction Catalyst: Flexible Electron Manipulation and Adaptive Coordination on a Dinuclear Cobalt Complex

Metal complexes with flexible redox and coordination properties possibly act as ingenious electrocatalysts to activate stable molecules such as CO₂. To date, most studies have focused on mononuclear complexes in electrochemical CO₂ reduction (eCO₂R). However, the development of electrocatalysts that operate at low overpotentials while maintaining high selectivity remains a critical challenge. Herein, it is demonstrated that the use of a dinuclear metal complex exhibiting cooperation of two metal centers can be an effective strategy for addressing this issue. The focused catalyst is a Co^II dinuclear complex (2) bearing two Co^II ions in close proximity, whose coordination environment is similar to that of a typical mononuclear complex, Co^II tetraphenylporphyrin (1). Based on experimental and computational studies, it is clarified that 2 exhibits simultaneous two-electron reduction prior to CO₂ activation, which allows bypassing the reaction step that hinders the catalytic cycle on 1. Furthermore, metal-to-metal electron transfer and a CO₂-derived intermediate bridging over two metal centers are found in the catalytic cycle of 2, which would contribute to low activation barrier. It is then concluded that the cooperative functions of the two metal centers are the key to the efficient eCO₂R performance.