Cluster build-up using the [Os(η⁶-C₆H₆)(MeCN)₃]²⁺cation; Synthesis and structural characterisation of some hexa- and hepta-nuclear arene-substituted clusters

Reactions of the cluster dianion [Os5(CO)15]2-with [Os(η6-C6H6)(MeCN)3]2+and [Os(C6H5Me)(CF3SO3)2] provided [Os6(CO)15(η6-C6H6)] 1 and [Os6(CO)15(η6-C6H5Me)] 2, respectively, in good yield (≈45%). Reduction of the hexaosmium cluster [Os6(CO)18] with K-Ph2CO gave the cluster dianion [Os6(CO)17]2-3 in quantitative yield. When this dianion was treated with [Os(η6-C6H6)(MeCN)3]2+the heptanuclear cluster [Os7(CO)17(η6-C6H6)] 4 was obtained in fair yield, while the corresponding reaction with [Os(η6-C6H5Me)(CF3SO3)2] gave [Os7(CO)17(η6-C6H5Me)] 5 in similar yield (ca. 25%). The four arene clusters have been characterised by spectroscopic techniques, and the molecular geometries of 1, 2 and 4 established by single-crystal X-ray diffraction techniques. In both 1 and 2 the metal framework geometry is best described as a bicapped tetrahedron. In 1 the η6-C6H6ligand occupies a site on the central Os4tetrahedron while in 2 in the η6-arene is co-ordinated to one of the capping Os atoms. The metal framework in 4 may be viewed as derived from a bicapped tetrahedron with the seventh metal capping one of the caps to give a chain of four fused tetrahedra. The η6-C6H6ligand in 4 occupies a similar site to that found in 1.