Hydrogenation of carboxylic esters catalyzed by manganese catalysts supported by bidentate NHC-phosphine ligands

Abstract

A series of bidentate manganese complexes with a general structure [(κ2C,P-R2PCH2CH2-NHC)Mn(CO)3Br] (NHC = N-substituted imidazolylidene) was prepared and fully characterized. These complexes were proven to be efficient catalysts for the hydrogenation of carboxylic ester derivatives with a low catalyst loading (0.5 mol%) in 2-Me-THF at 100 °C in the presence of KHBEt3. The generality of this hydrogenation was exemplified with more than 25 substrates. Experimental and computational investigations allowed to propose a rational mechanism involving an anionic tricarbonyl manganese hydride complex as the active species.