Kinetics of the Effect in Ruthenium Complexes Provide Insight into the Factors That Control Activity and Stability in CO Electroreduction.

Comparative kinetic studies of a series of new ruthenium complexes provide a platform for understanding how strong effect ligands and redox-active ligands work together to enable rapid electrochemical CO reduction at moderate overpotential. After synthesizing isomeric pairs of ruthenium complexes featuring 2'-picolinyl-methyl-benzimidazol-2-ylidene (Mebim-pic) as a strong effect ligand and 2,2':6',2″-terpyridine (tpy) as a redox-active ligand, chemical and electrochemical kinetic studies examined how complex geometry and charge affect the individual steps and overall catalysis of CO reduction. The relative effect of picoline vs the N-heterocyclic carbene (NHC) was quantified through a kinetic analysis of reductively triggered chloride dissociation, revealing that chloride loss is 1000 times faster in the isomer with the NHC to chloride.