SYNTHESIS, STRUCTURE, AND FLUXIONAL BEHAVIOR OF BASE-STABILIZED SILYL(SILYLENE)TUNGSTEN COMPLEXES

Donor-stabilized silyl(silylene)tungsten complexes Cp(OC)(2)W(SiMe3)(= SiMe2 . Base) (Cp = eta-C5H5, Base = HMPA (1a) and THF (1b)) have been synthesized by photolysis of C6D6 solutions containing CpW(CO)(3)-SiM e2SiMe3 and bases. The double-bond character of the tungsten-silylene bonding was revealed by the significant downfield shift of the Si-29 N MR signal as well as the Large (1)J(WSi) value for the silylene ligand (delta = 92.5 ppm ((1)J(WSi) = 121 HZ) for 1 and delta = 144.7 ppm (( 1)J(WSi) = 132 Hz) for Ib) and also the short W-Si distance between tu ngsten and the silylene ligand (2.481(3) Angstrom) of la. Complex Ib s hows fluxional behavior due to intramolecular 1,3-methyl migration fro m the silyl ligand to the silylene ligand.