Hydrogenation of Alkenes Catalyzed by Mn(I) Alkyl Complexes Bearing NHC Phosphine Ligands

An efficient additive free hydrogenation of alkenes with molecular hydrogen is described. The pre‐catalyst is a well‐defined bench stable Mn(I) alkyl complex bearing a NHC phosphine ligand. These reactions are environmentally benign and atom economic, implementing an inexpensive, earth abundant non‐precious metal catalyst. The catalytic process is initiated by migratory insertion of a CO ligand into the Mn‐alkyl bond to yield an acyl intermediate which undergoes rapid hydrogenolysis to form the active 16e Mn(I) hydride catalyst [Mn(PC‐ i Pr)(CO) 2 (H)]. A range of mono‐ and disubstituted alkenes were efficiently converted into alkanes in good to excellent yields. The hydrogenation requires a reaction temperature of 60 °C. In all cases, a catalyst loading of 1 mol % and a hydrogen pressure of 50 bar was applied. A mechanism based on DFT calculations is presented which is supported by experimental studies.