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

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.