ASYMMETRIC ALKYLIDENE AND OXO COMPLEXES OF TUNGSTEN(VI)

Reactions between (t-BuO)3W(=CR) derivatives and 1,1'-bi-2-naphthols ( H2R2BINO, R = Me,Br,Ph) generate mononuclear C1-symmetric (R2BINO)(t-B uO)2W(=CHR) complexes. An analogous reaction with 2 equiv of H2Me2BINO generates (Me2BINO)2W(=CHPh), while a reaction between H2Me2BINO and (t-BuO)4W(=O) produces (Me2BINO)(t-BuO)2W(=O). This oxo complex was ch aracterized by X-ray crystallography, which shows it to be a highly-di storted trigonal bipyramidal complex in which the Me2BINO ligand adopt s a lambda chelate stereochemistry. Although the complexes show little stereoselectivity in Wittig-like alkylidene transfer to benzaldehyde, the ring opening metathesis polymerization of norbornene proceeds wit h modest stereoselectivity. The fraction of cis-polynorbornene increas es in concert with the steric demands of the substituents on the R2BIN O ligand. Crystal data for (Me2BINO)(t-BuO)2W(=O) at 113 K: a = 11.426 (3) angstrom, b = 14.733(3) angstrom, c = 16.716(4) angstrom, beta = 1 05.87(2)degrees, Z = 4, D(calc.) = 1.616, space group P2(1)/n (No. 14) , R(F) = 0.053, R(w)(F) = 0.106 for 3451 reflections (F(o) > 0).