Activating a Low Overpotential CO 2 Reduction Mechanism by a Strategic Ligand Modification on a Ruthenium Polypyridyl Catalyst

The introduction of a simple methyl substituent on the bipyridine ligand of [Ru( t Bu 3 tpy)(bpy)(NCCH 3 )] 2+ ( t Bu 3 tpy=4,4′,4′′‐tri‐ tert ‐butyl‐2,2′:6′,2′′‐terpyridine; bpy=2,2′‐bipyridine) gives rise to a highly active electrocatalyst for the reduction of CO 2 to CO. The methyl group enables CO 2 binding already at the one‐electron reduced state of the complex to enter a previously not accessible catalytic cycle that operates at the potential of the first reduction. The complex turns over with a Faradaic efficiency close to unity and at an overpotential that is amongst the lowest ever reported for homogenous CO 2 reduction catalysts.