Mixed-metal cluster chemistry

Abstract

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.