FACILE SYNTHESIS OF CATIONIC TUNGSTEN(VI) ALKYLIDENE COMPLEXES

The synthesis of a series of oxygen- and moisture-stable tungsten(VI) alkylidene complexes containing the hydridotris(pyrazolyl)borate (Tp) ligand is described. The complexes, TpW(CHCMe2R)(CH2CMe2R)(NAr) [R = Me, Ar = Ph; R = Ph, Ar = Ph; R = Ph, Ar = 2,6-i-Pr2C6H5), 5-7, are formed in the reaction between KTp and W(CH2CMe2R)3(NAr)Cl. Complexes 5-7 are protonated by the noncoordinating Bronsted acid [H(OEt2)2]{B[(3,5-CF3)2C6H3]4} giving the cationic alkylidene complexes [TpW(NPh)(CHCMe3)(S)][BAr*4] (S = Et2O, i-Pr2O, CH3-CN, Ar* = (3,5-CF3)2C6H3), 8-10. The cationic amido oxo alkyl complex [TpW(NHPh)(O)-(CH2CMePh)][BF4], 12, is formed when 6 is protonated with HBF4 in the presence of 1 equiv of H2O. Compounds 5-7 function as catalyst precursors for the ring-opening polymerization of cyclooctene and are activated by Lewis acid cocatalysts such as AlCl3.