High Oxidation State Molybdenum Imido Heteroatom-Substituted Alkylidene Complexes

Reactions between Mo(NAr)(CHR)(Me 2 Pyr)(OTPP) (Ar = 2,6- i -Pr 2 C 6 H 3, R = H or CHCMe 2 Ph, Me 2 Pyr = 2,5-dimethylpyrrolide, OTPP = O-2,3,5,6-Ph 4 C 6 H) and CH 2 ═CHX where X = B(pin), SiMe 3, N -carbazolyl, N -pyrrolidinonyl, PPh 2, OPr, or SPh lead to Mo(NAr)(CHX)(Me 2 Pyr)(OTPP) complexes in good yield. All have been characterized through X-ray studies (as an acetonitrile adduct in the case of X = PPh 2 ). The efficiencies of metathesis reactions initiated by Mo(NAr)(CHX)(Me 2 Pyr)(OTPP) complexes can be rationalized on the basis of steric factors; electronic differences imposed as a consequence of X being bound to the alkylidene carbon do not seem to play a major role. Side reactions that promote catalyst decomposition do not appear to be a serious limitation for Mo═CHX species.