Electrocatalytic CO2 Reduction with Re-Based Spiro Bipyridine Complexes: Effects of the Local Proton in the Second Coordination Sphere†

We report herein a Re-based tricarbonyl catalyst [fac-Re(L1)(CO)Cl] (Re1) bearing a spiro center and a phenol group as a local proton source in the second coordination sphere. Due to the large steric spiro group, dimerization of one-electron reduced species was completely eliminated, improving the stability of Re1. Simultaneously, the phenol group in the second coordination sphere improves the formation of an H-bonding chain that promotes the protonation of CO reduction intermediates, boosting the electrocatalytic CO reduction activity of Re1. Mechanistic studies reveal that the doubly reduced complex Re1b is active for CO addition.