Synthesis and characterisation of the tetranuclear phosphinidene clusters [Os3MH2(CO)12(PR)](M = Os, R = Ph or cyclo-C6H11; M = Ru, R = cyclo-C6H11) and the crystal and molecular structure of [Os4(µ-H)2(CO)12(µ3-PC6H11)]

Abstract

Reaction of the phosphinidene-capped cluster [Os₃H₂(CO)₉(PR)](R = Ph or cyclo-C₆H₁₁) with the binary carbonyl [M₃(CO)₁₂](M = Ru or Os), under reflux in nonane, affords the tetranuclear clusters [Os₃MH₂(CO)₁₂(PR)][(1) M = Os, R = Ph; (2) M = Os, R = cyclo-C₆H₁₁; (3) M = Ru, R = cyclo-C₆H₁₁] together with the previously reported penta- and hexa-nuclear clusters [Os₃M₂(CO)₁₅(PR)] and [Os₃M₃(CO)₁₇(PR)]. The structure of (2) has been established by an X-ray analysis which shows that there are two independent but structurally similar tetranuclear clusters per asymmetric unit. Within each molecule the four Os atoms adopt a ‘butterfly’ arrangement, consistent with the 62-electron count, and the phosphinidene ligand bridges an open triangular face defined by one ‘bridge’ and two ‘wingtip’ Os atoms. The 12 carbonyl ligands are terminal, and the two hydrides bridge the two remaining ‘hinge’ to ‘wingtip’ Os–Os edges. Solution ¹H and ³¹P n.m.r. spectra for clusters (1)–(3) are consistent with this ground-state structure, and the positions of the hydrides are confirmed by the observation of ¹⁸⁷Os satellites in the ¹H n.m.r. spectra of (1) and (2). The cluster (3) exists as a mixture of three inseparable isomers which arise from the juxtaposition of the Ru atom around the three inequivalent positions of the metal ‘butterfly’. The existence of these isomers is confirmed by a detailed analysis of the ¹H and ³¹P n.m.r. spectra of this complex.