Syntheses and reactions of ansa-[2,2-bis(η-cyclopentadienyl)propane]-tungsten and -molybdenum compounds

Abstract

Reaction between [MCl₄(dme)](M = W or Mo; dme = 1,2-dimethoxyethane) with Li₂[C₅H₄CMe₂C₅H₄] gave the ansa-bridged metallocene dichlorides [M{(η-C₅H₄)CMe₂(η-C₅H₄)}Cl₂](M = W or Mo). Treatment of these with LiAlH₄ or ZnMe₂ gave respectively the dihydrides [M{(η-C₅H₄)CMe₂(η-C₅H₄)}H₂](M = W or Mo) and the dimethyl derivatives [M{(η-C₅H₄)CMe₂(η-C₅H₄)}Me₂](M = W or Mo). Treatment of [W{(η-C₅H₄)CMe₂(η-C₅H₄)}Me₂] with HX (X = PhCO₂ or NH₃l) gave [W{(η-C₅H₄)CMe₂(η-C₅H₄)}Me(Y)] with Y = PhCO₂ or l, respectively. Both of these react with Na[AlH₂(OCH₂CH₂OMe)₂] giving the methylhydride [W{(η-C₅H₄)CMe₂(η-C₅H₄)}Me(H)]. The latter is thermally stable in refluxing benzene. Ultraviolet photolysis of [Mo{(η-C₅H₄)CMe₂(η-C₅H₄)}H₂] in benzene gave the phenylhydride derivative [Mo{(η-C₅H₄)CMe₂(η-C₅H₄)}Ph(H)]; the corresponding tungsten derivative [W{(η-C₅H₄)CMe₂(η-C₅H₄)}H₂] is not photosensitive. The crystal structures of [W{(η-C₅H₄)CMe₂(η-C₅H₄)}Cl₂], [W{(η-C₅H₄)CMe₂(η-C₅H₄)}H₂], (two modifications) and [Mo{(η-C₅H₄)CMe₂(η-C₅H₄)}H₂] have been determined by X-ray diffraction. The ansa-bridged bis(η-cyclopentadienyl) compounds show marked differences in reactivity compared to non-ansa analogues and this is discussed in terms of the modifications of the electronic structure as a consequence of the ansa bridge.