Effect of Unique NNS Ligand in Manganese‐Catalyzed Transfer Hydrogenation Reaction—A DFT Mechanistic Study

ABSTRACT The transfer hydrogenation between isopropanol and acetophenone catalyzed by phosphine‐free cationic [NNS‐Mn(CO) 3 ] + complexes bearing sulfur‐arm ligand has been computed. Since base treatment can have two active amido complexes, bidentate NN‐Mn(CO) 3 with sulfur‐arm ligand as spectator or tridentate NNS‐Mn(CO) 2 involving the sulfur‐arm have been considered. The bidentate complexes are more active in isopropanol dehydrogenation, and the tridentate complexes are more active in acetophenone hydrogenation; however, both complexes have rather low apparent barriers, rationalizing the reaction conditions at room temperature and ambient pressure. It is noted that isopropanol dehydrogenation prefers an outer‐sphere mechanism and represents the rate‐determining step. On the contrary to isopropanol as a hydrogen source, activation of H 2 has a much higher barrier, explaining the rather lower activity under harsh conditions at high temperature and high pressure.