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

Reactions of [Cp2W2Ir2(CO)(10)] with stoichiometric amounts of trimethylpho sphite afford the substitution products [Cp2W2Ir2(mu-CO)(3)(CO)(7 - n){P(OM e)(3)}(n)] [n = 1 (2) or 2 (3)]. A structural study of 3 reveals that the t hree edges of a WIr2 face of the tetrahedral core are spanned by bridging c arbonyls, and that the iridium-bound P(OMe)(3) groups ligate radially and a xially with respect to the plane of bridging carbonyls. The tungsten-bound eta(5)-cyclopentadienyl groups ligate axially and apically with respect to the plane of bridging carbonyls. An unusual decomposition reaction was obse rved 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 previou sly synthesized [CpWIr3(mu-Co)(3)(Co)(7){P(OMe)(3)}] (4). A structural stud y 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 irid ium-bound P(OMe)(3) and the tungsten-bound eta(5)-cyclopentadienyl moieties ligate diaxially with respect to the plane of bridging carbonyls. Monitori ng a solution of 3 by P-31-NMR spectroscopy reveals slow formation of 4 (93 % 3: 7% 4 over 4 days) at room temperature. One configuration only of clust ers 2 and 3 was observed in the C-13- and P-31-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 formulati on 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(mu-CO)(3)(CO)(6)(PMe3)] (M = Mo, W), the molybd enum analogue of which has been structurally characterized previously. (C) 1999 Elsevier Science S.A. All rights reserved.