Asymmetric alkylidene and oxo complexes of tungsten(VI)

Article abstract of DOI:10.1021/om00031a029

Reactions between (t-BuO)₃W(≡CR) derivatives and 1,1′-bi-2-naphthols (H₂R₂BINO, R = Me, Br, Ph) generate mononuclear C₁-symmetric (R₂BINO) (t-BuO)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 characterized by X-ray crystallography, which shows it to be a highly-distorted trigonal bipyramidal complex in which the Me₂BINO ligand adopts a λ chelate stereochemistry. Although the complexes show little stereoselectivity in Wittig-like alkylidene transfer to benzaldehyde, the ring opening metathesis polymerization of norbornene proceeds with modest stereoselectivity. The fraction of cis-polynorbornene increases in concert with the steric demands of the substituents on the R₂BINO ligand. Crystal data for (Me₂BINO)(t-BuO)₂W(=O) at 113 K: a = 11.426(3) A?, b = 14.733(3) A?, c = 16.716(4) A?, β = 105.87(2)°, Z = 4, D_calc = 1.616, space group P2₁/n (No. 14), R(F) = 0.053, R_w(F) = 0.106 for 3451 reflections (F_o > 0).