Mechanistic Studies on the Alkylation of Amines with Alcohols Catalyzed by a Bifunctional Iridium Complex

The mechanism of the N-alkylation of amines with alcohols catalyzed by an iridium complex containing an N-heterocyclic carbene (NHC) ligand with a tethered alcohol/alkoxide functionality was investigated by a combination of experimental and computational methods. The catalyst resting state is an iridium hydride species containing the amine substrate as a ligand, and decoordination of the amine, followed by coordination of the imine intermediate to the iridium center, constitute the rate-determining step (rds) of the catalytic process. The alcohol/alkoxide that is tethered to the NHC participates in every step of the catalytic cycle by accepting or releasing protons and forming hydrogen bonds with the reacting species. Thus, the iridium complex with the alcohol/alkoxide tethered to the N-heterocyclic carbene ligand acts as a bifunctional catalyst.