Hydrogenation of Carboxylic Esters Catalyzed by Phosphine-Free Bis-N-heterocyclic Carbene Manganese Complexes

As an earth-abundant transition metal, manganese is now recognized as a good candidate for the development of catalysts for reduction-type reactions. It is often associated with a noninnocent tridentate ligand, featuring an acidic NH moiety. We report here that a simple bidentate and phosphine-free bis-N-heterocyclic ligand associated with manganese in the complex [Mn­(bis-NHCMes)­(CO)3Br] could catalyze the hydrogenation of carboxylic esters in the presence of KBHEt3 as an activator at 100–120 °C under 50 bar of H2 at 1 mol % catalyst loading in 2-Me-THF.