Phosphine-NHC Manganese Hydrogenation Catalyst Exhibiting a Non-Classical Metal-Ligand Cooperative H 2 Activation Mode

Deprotonation of the Mn NHC-phosphine complex fac-[MnBr(CO) (κ P,C-Ph PCH NHC)] (2) under a H atmosphere readily gives the hydride fac-[MnH(CO) (κ P,C-Ph PCH NHC)] (3) via the intermediacy of the highly reactive 18-e NHC-phosphinomethanide complex fac-[Mn(CO) (κ P,C,C-Ph PCHNHC)] (6 a). DFT calculations revealed that the preferred reaction mechanism involves the unsaturated 16-e mangana-substituted phosphonium ylide complex fac-[Mn(CO) (κ P,C-Ph P=CHNHC)] (6 b) as key intermediate able to activate H via a non-classical mode of metal-ligand cooperation implying a formal λ -P-λ -P phosphorus valence change. Complex 2 is shown to be one of the most efficient pre-catalysts for ketone hydrogenation in the Mn series reported to date (TON up to 6200).