Cationic molybdenum oxo alkylidenes stabilized by N-heterocyclic carbenes: from molecular systems to efficient supported metathesis catalysts

Cationic d(0) group 6 olefin metathesis catalysts have been recently shown to display in most instances superior activity in comparison to their neutral congeners. Furthermore, their catalytic performance is greatly improved upon immobilization on silica. In this context, we have developed the new family of molecular cationic molybdenum oxo alkylidene complexes stabilized by N-heterocyclic carbenes of the general formula [Mo(O)(CHCMe(3))(IMes)(OR)[X(−)]] (IMes = 1,3-dimesitylimidazol-2-ylidene; R = 1,3-dimesityl-C(6)H(3), C(6)F(5); X(−) = B(3,5-(CF(3))(2)C(6)H(3))(4)(−), B(Ar(F))(4), tetrakis(perfluoro-t-butoxy)aluminate (PFTA)). Immobilization of [Mo(O)(CHCMe(3))(IMes)(O-1,3-dimesityl-C(6)H(3))(+)B(Ar(F))(4)(−)] on silica via surface organometallic chemistry yields an active alkene metathesis catalyst that shows the highest productivity towards terminal olefins amongst all existing molybdenum oxo alkylidene catalysts.