Mechanistic Studies on the NNN Pincer-Ruthenium Catalysed Transformation of Ethanol to Ethyl Acetate

Abstract

NNN pincer-Ru complex Cy2NNN(RuCl2)(PPh3) [0.08M] based on bis(imino)pyridine ligand efficiently brings about the catalytic dehydrogenative coupling of ethanol resulting in up to 1.32 M of ethyl acetate in the presence of 0.25 M KOtBu at 120 °C after 24h. Mechanistic insights revealed PPh3 dissociation as a key to activation, while mercury poisoning tests revealed the molecular nature of the active species. Isotope-labeling studies indicates a non-rate-limiting C-H cleavage step. DFT studies of the catalytic cycle involving an inner sphere, metal-centred mechanism suggest alcoholysis as the rate-limiting step, with a barrier 21.3 kcal/mol.