Evidence for a reversible 1,2-hydrogen shift (α elimination) in some bis(η-cyclopentadienyl)tungsten compounds

Abstract

The reaction of [W(η-C₅H₅)₂(C₂H₄)Me][PF₆] with PMe₂Ph gives [W(η-C₅H₅)₂(CH₂CH₂PMe₂Ph)Me][PF₆](2) which eliminates ethylene when heated to give, in sequence, [W(η-C₅H₅)₂(CH₂PMe₂Ph)H][PF₆](3) and [W(η-C₅H₅)₂Me(PMe₂Ph)][PF₆](4). Repeating this sequence with the deuteriated methyl analogues shows that the CD₃ unit in (2) is reformed quantitatively in (4) and supports the proposal that the mechanism of the reaction involves a reversible 1,2-hydrogen shift equilibrium between the intermediates [W(η-C₅H₅)₂Me]⁺ and [W(η-C₅H₅)₂(CH₂)H]⁺. The compounds [W(η-C₅H₅)₂L(Me)](L = SEt₂ or PPh₃) and [W(η-C₅H₅)₂Me(I)] have also been prepared and treated with PMe₂Ph to give (3). Some implications of the 1,2-hydrogen shift (α elimination) are discussed.