Old Concepts, New Application - Additive-Free Hydrogenation of Nitriles Catalyzed by an Air Stable Alkyl Mn(I) Complex

An efficient additive-free manganese-catalyzed hydrogenation of nitriles to primary amines with molecular hydrogen is described. The pre-catalyst, a well-defined bench-stable alkyl bisphosphine Mn(I) complex fac-[Mn(dpre)(CO)(3)(CH3)] (dpre=1,2-bis(di-n-propylphosphino)ethane), undergoes CO migratory insertion into the manganese-alkyl bond to form acyl complexes which upon hydrogenolysis yields the active coordinatively unsaturated Mn(I) hydride catalyst [Mn(dpre)(CO)(2)(H)]. A range of aromatic and aliphatic nitriles were efficiently and selectively converted into primary amines in good to excellent yields. The hydrogenation of nitriles proceeds at 100 degrees C with a catalyst loading of 2 mol % and a hydrogen pressure of 50 bar. Mechanistic insights are provided by means of DFT calculations.