Oxidative-addition reactions of [W2(η-C5H4R)2X4](R = Pri or Me; X = Cl or Br): reversible addition of dihydrogen to a tungsten–tungsten triple bond and X-ray crystal structures of [W2(η-C5H4Pri)2Cl4(µ-H)(µ-PPh2)] and [W2(η-C5H4Pri)2Cl3(µ-Cl)(µ-H)(µ-PPh2)(PMe3)]

Abstract

The unsupported WW bond of [W₂(η-C₅H₄R)₂X₄](X = Cl, R = Prⁱ1a or Me 1b; X = Br, R = Prⁱ2) readily undergoes oxidative-addition reactions with HY [Y = H, Cl, SR′(R′= Me, Et, Prⁱ, Ph or Bu^t), or PPhR′(R′= H or Ph)] to afford the corresponding derivatives [W₂(η-C₅H₄R)₂X₄(µ-H)(µ-Y)] in good yields. For 1a the addition of H₂ is reversible with reductive elimination occurring readily at ca. 50 °C under reduced pressure. The µ-phosphido complex [W₂(η-C₅H₄Prⁱ)₂Cl₄(µ-H)(µ-PPh₂)] has been crystallographically characterised and possesses a WW double bond [2.6558(3)Å]. The µ-thiolato complexes [W₂(η-C₅H₄R)₂Cl₄(µ-H)(µ-SR′)] are fluxional and undergo inversion at the µ-S atom; ΔG^‡ values for this process have been determined and increase in the order R′= Bu^t < Prⁱ < Ph < Et < Me. The µ-chloro complexes [W₂(η-C₅H₄R)₂Cl₄(µ-Cl)(µ-H)] undergo a different fluxional process which effectively involves rotation of the (µ-Cl)(µ-H) fragment about the W–W vector. The complexes [W₂(η-C₅H₄Prⁱ)₂Cl₄(µ-H)(µ-Y)](Y = H or PPh₂) react with PMe₃ to give the corresponding adducts [W₂(η-C₅H₄Prⁱ)₂Cl₃(µ-Cl)(µ-H)(µ-Y)(PMe₃)], the X-ray crystal structure of the µ-phosphido complex (Y = PPh₂) having been determined. In contrast, treatment of [W₂(η-C₅H₄Prⁱ)₂Cl₄(µ-H)(µ-Y)](Y = Cl or SR′) with an excess of PMe₃ affords the mononuclear complex [W(η-C₅H₄Prⁱ)Cl(PMe₃)₃].