REACTION OF A TUNGSTEN(II) METHYLENE COMPLEX WITH EXCESS BASE TO FORMA C3H5-BRIDGED DIMER

Reaction of [Tp'(CO)(PhC2Me)W=CH2][PF6] (1) with excess base (NaOH/H2O or KH) in methylene chloride yields the C3H5-bridged dimer [Tp'(CO)(P hC2Me)WCH2C(H)CH2W(PhC2 Me)(CO)Tp'][PF6] (2), Dimer 2 is reproducibly formed in yields of 10-15%; it is inert toward a variety of nucleophil es. Structural and spectroscopic features of 2 form the basis for a di scussion of the bonding in this unusual complex, Bonding extremes for the hydrocarbon bridge include an allylic C3H5 fragment bound to the t wo tungsten centers through opposite faces of the allyl ligand, a link age which is sigma-bonded at each metal with a carbocationic central c arbon, and a sigma,pi-bridging system, Metric parameters in the solid state and H-1, C-13 NMR and infrared spectroscopies suggest that the d ominant resonance contribution, derives from the allylic formalism. A surrogate solvent (1,2-dichloroethane) results in no observable change in the reaction, and thus, the methide source needed to link the two monomeric fragments is believed to originate from the carbene complex.