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

Deprotonation of the Mn I NHC‐phosphine complex fac‐[MnBr(CO) 3 (κ 2 P,C‐Ph 2 PCH 2 NHC)] ( 2 ) under a H 2 atmosphere readily gives the hydride fac‐[MnH(CO) 3 (κ 2 P,C‐Ph 2 PCH 2 NHC)] ( 3 ) via the intermediacy of the highly reactive 18‐e NHC‐phosphinomethanide complex fac‐[Mn(CO) 3 (κ 3 P,C,C‐Ph 2 PCHNHC)] ( 6 a ). DFT calculations revealed that the preferred reaction mechanism involves the unsaturated 16‐e mangana‐substituted phosphonium ylide complex fac‐[Mn(CO) 3 (κ 2 P,C‐Ph 2 P=CHNHC)] ( 6 b ) as key intermediate able to activate H 2 via a non‐classical mode of metal‐ligand cooperation implying a formal λ 5 ‐P–λ 3 ‐P phosphorus valence change. Complex 2 is shown to be one of the most efficient pre‐catalysts for ketone hydrogenation in the Mn I series reported to date (TON up to 6200).