Hydride, gold(i) and related derivatives of the unsaturated ditungsten anion [W2Cp2(μ-PCy2)(μ-CO)2]−

Abstract

Protonation of the title anion with [NH₄]PF₆ gave [W₂Cp₂(H)(μ-PCy₂)(CO)₂] (2), which in solution exists as an equilibrium mixture of two isomers having either bridging (major) or terminal (minor) hydrides. Both molecules retain short intermetallic distances (ca. 2.54 Å), with the H-bridged isomer being almost 15 kJ mol⁻¹ more stable than the terminal one, according to density functional theory calculations. Further protonation with acids having weakly coordinating anions (BF₄⁻ or BAr′₄⁻; Ar′ = 3,5-C₆H₃(CF₃)₂) yielded isomeric cations also displaying bridging and terminal hydride ligands ([W₂Cp₂(μ-H)(H)(μ-PCy₂)(CO)₂]⁺ and [W₂Cp₂(H)₂(μ-PCy₂)(CO)₂]⁺), with the latter being only slightly more energetic (by ca. 4 kJ mol⁻¹). In contrast, protonation of 2 with carboxylic acids yielded carboxylate-bridged derivatives [W₂Cp₂(μ-PCy₂)(μ-O:O′-O₂CR)(CO)₂] [R = Ph, CF₃] following from dihydrogen elimination. The title anion also reacted readily with metal-based electrophiles such as ClSnPh₃ and [AuCl(PR₃)] (R = ⁱPr, p-tol) to give the corresponding heterometallic clusters [W₂Cp₂(μ-PCy₂)(μ-SnPh₃)(CO)₂] and [AuW₂Cp₂(μ-PCy₂)(CO)₂(PR₃)], these having the added electrophile placed at the bridging position and formally retaining triple W–W bonds. The gold complexes, however, were rather unstable species decomposing spontaneously to give the tetranuclear clusters [Au₂W₂Cp₂(μ-PCy₂)(CO)₂(PR₃)₂]X (W–W = 2.5803(6) Å and Au–Au = 2.8050(6) Å when R = ⁱPr and X = PF₆), which could be prepared more conveniently by adding two equivalents of [AuCl(PR₃)] to the anion, as expected. In contrast, reaction of the title anion with ClPbPh₃ led to the formation of the phenyl-bridged complex [W₂Cp₂(μ-PCy₂)(μ-Ph)(CO)₂], following from the formal loss of PbPh₂.