Activating a Low Overpotential CO2 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(tBu3tpy)(bpy)(NCCH3)]2+ (tBu3tpy=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 CO2 to CO. The methyl group enables CO2 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 CO2 reduction catalysts. Simple and effective: The steric effect of a CH3 group at the ortho position of a bipyridine ligand activates a previously unreactive oxidation state in a RuII polypyridyl complex and enables electrocatalytic CO2 reduction at the potential of the first one‐electron reduction. The mechanistic pathway operates at an overpotential of η=0.47 V, about 400 mV less than in the absence of the methyl group.