Mixed-metal cluster chemistry: Part 14: Reaction of [Cp₂W₂Ir₂(CO)₁₀] with trimethylphosphite; X-ray crystal structures of [Cp₂W₂Ir₂(μ-CO)₃(CO) ₅{P(OMe)₃}₂] and two modifications of [CpWIr₃(μ-CO)₃(CO)₇{P(OMe)₃}]

Reactions of [Cp₂W₂Ir₂(CO)₁₀] with stoichiometric amounts of trimethylphosphite afford the substitution products [Cp₂W₂Ir₂(μ-CO)₃(CO) _7-n{P(OMe)₃}_n] [n=1 (2) or 2 (3)]. A structural study of 3 reveals that the three edges of a WIr₂ face of the tetrahedral core are spanned by bridging carbonyls, and that the iridium-bound P(OMe)₃ groups ligate radially and axially with respect to the plane of bridging carbonyls. The tungsten-bound η⁵-cyclopentadienyl groups ligate axially and apically with respect to the plane of bridging carbonyls. An unusual decomposition reaction was observed during the crystallization of 3. A single-crystal X-ray study from the second type of crystals from a solution of 3 was identified as the previously synthesized [CpWIr₃(μ-CO)₃(CO)₇{P(OMe)₃}] (4). A structural study of 4 reveals that the cluster core has a WIr₃ tetrahedral framework, with three edges of a WIr₂ face spanned by bridging carbonyls and that the iridium-bound P(OMe)₃ and the tungsten-bound η⁵-cyclopentadienyl moieties ligate diaxially with respect to the plane of bridging carbonyls. Monitoring a solution of 3 by ³¹P-NMR spectroscopy reveals slow formation of 4 (93% 3: 7% 4 over 4 days) at room temperature. One configuration only of clusters 2 and 3 was observed in the ¹³C- and ³¹P-NMR spectra (between 183 and 303 K), with no evidence for the presence of additional isomers undergoing very fast exchange. The NMR spectra of 3 are consistent with the formulation given in the X-ray crystallographic study. The NMR spectra of 2 suggest a configuration with axial phosphite, axial Cp, apical Cp, analogous to the related clusters [Cp₂M₂Ir₂(μ-CO)₃(CO) ₆(PMe₃)] (M=Mo, W), the molybdenum analogue of which has been structurally characterized previously.