Molybdenum (0) and tungsten (0) carbonyl N-heterocyclic carbene complexes as catalyst for olefin epoxidation

A series of Mo(0) and W(0) carbonyl N-heterocyclic carbene (NHC) complexes containing monodentate NHC ligands with the formulae of M(CO)4(NHC)2 (NHC = IBz = 1,3-dibenzylimidazol-2-ylidene, M = Mo (1a), W (2a); NHC = InPr = 1,3-dipropylimidazol-2-ylidene, M = Mo (3), W (4a)) and M(CO)5(NHC) (NHC = IBz, M = Mo (1b), W (2b); NHC = InPr, M = W (4b); NHC = IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene, M = Mo (5), W (6)) and the complexes containing chelating NHC ligands Mo(CO)4(PyNHC) (PyNHC = 3-methyl-1-picolylimidazol-2-ylidene (7)) and Mo(CO)3(Py2NHC) (Py2NHC = 1,3-dipicolylimidazol-2-ylidene (8)) have been synthesized and fully characterized. They show moderate catalytic activities towards cyclooctene epoxidation in the presence of tert-butyl hydroperoxide (TBHP). The stability of Mo–CNHC bond under oxidative condition has been investigated.