Elevated catalytic activity of ruthenium(II)–porphyrin-catalyzed carbene/nitrene transfer and insertion reactions with N-heterocyclic carbene ligands

Abstract

Bis(NHC)ruthenium(II)–porphyrin complexes were designed, synthesized, and characterized. Owing to the strong donor strength of axial NHC ligands in stabilizing the trans M[DOUBLE BOND]CRR′/M[DOUBLE BOND]NR moiety, these complexes showed unprecedently high catalytic activity towards alkene cyclopropanation, carbene C[BOND]H, N[BOND]H, S[BOND]H, and O[BOND]H insertion, alkene aziridination, and nitrene C[BOND]H insertion with turnover frequencies up to 1950 min−1. The use of chiral [Ru(D4-Por)(BIMe)2] (1 g) as a catalyst led to highly enantioselective carbene/nitrene transfer and insertion reactions with up to 98 % ee. Carbene modification of the N terminus of peptides at 37 °C was possible. DFT calculations revealed that the trans axial NHC ligand facilitates the decomposition of diazo compounds by stabilizing the metal–carbene reaction intermediate.