The Trans Effect in Electrocatalytic CO Reduction: Mechanistic Studies of Asymmetric Ruthenium Pyridyl-Carbene Catalysts.

A comprehensive mechanistic study of electrocatalytic CO reduction by ruthenium 2,2':6',2″-terpyridine (tpy) pyridyl-carbene catalysts reveals the importance of stereochemical control to locate the strongly donating N-heterocyclic carbene ligand trans to the site of CO activation. Computational studies were undertaken to predict the most stable isomer for a range of reasonable intermediates in CO reduction, suggesting that the ligand trans to the reaction site plays a key role in dictating the energetic profile of the catalytic reaction. A new isomer of [Ru(tpy)(Mebim-py)(NCCH)] (Mebim-py is 1-methylbenzimidazol-2-ylidene-3-(2'-pyridine)) and both isomers of the catalytic intermediate [Ru(tpy)(Mebim-py)(CO)] were synthesized and characterized.