Cluster core geometrical variation in heterometallic boride clusters containing RhRu4 skeletons: crystal structures of [RhRu4H2(η5-C5Me5)(µ-Cl)(CO)12B] and [RhRu4H(nbd)(CO)12B(AuPPh3)](nbd = norbornadiene)
Abstract
The reaction of the butterfly anion [Ru4H(CO)12BH]– with [{Rh(η5-C5Me5)Cl2}2] gave the novel boron-containing cluster [RhRu4H2(η5-C5Me5)(µ-Cl)(CO)12B] which has been characterised spectroscopically and by X-ray crystallography. Consistent with the 78 valence-electron (v.e.) count, the five metal atoms adopt an open skeletal structure which can be described as an ‘envelope’(or an edge-bridged square) geometry. In contrast, when [Ru4H(CO)12BH]– reacted with [{Rh(nbd)Cl}2](nbd = norbornadiene) and [Au(PR3)Cl](R = Ph, C6H11 or 2-MeC6H4), boride clusters containing both RhRu4B and Rh2Ru4B skeletons were obtained. The presence of the gold(I) phosphine is necessary to trap the RhRu4B-containing product. The Rh2Ru4B clusters possess octahedral frameworks and are related to the previously reported [Rh2Ru4(CO)16B(AuPR3)] compounds. However, the incorporation of only one rhodium fragment leads to the clusters [RhRu4H(nbd)(CO)12B(AuPR3)], and a square-based pyramidal RhRu4 framework (consistent with a 74 v.e. count) has been confirmed by the results of a single-crystal X-ray diffraction study of [RhRu4H(nbd)(CO)12B(AuPPh3)]. Variable-temperature 1H NMR spectroscopic data for the clusters [RhRu4H(nbd)(CO)12B(AuPR3)](R = Ph, C6H11 or 2-MeC6H4) indicate fluxional behaviour involving the norbornadiene ligand and the gold(I) phosphine unit. The reaction of [RhRu4H(nbd)(CO)12B(AuPR3)](R = Ph or C6H11) with CO gave [RhRu4H(CO)14B(AuPR3)].