CLUSTER BUILDUP USING THE [OS(ETA-6-C6H6)(MECN)3]2+ CATION - SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF SOME HEXA-NUCLEAR AND HEPTA-NUCLEAR ARENE-SUBSTITUTED CLUSTERS

Reactions of the cluster dianion [Os5(CO)15]2- with [Os(eta6-C6H6)(MeCN3]2+ and [Os(C6H5Me)-(CF3SO3)2] provided [Os6(CO)15(eta6-C6H6)] 1 and [Os6(CO)15(eta6-C6H5Me)] 2, respectively, in good yield (almost-equal-to 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(eta6-C6H6)(MeCN)3]2+ the heptanuclear cluster [Os7(CO)17(eta6-C6H6)] 4 was obtained in fair yield, while the corresponding reaction with [Os(eta6-C6H5Me)(CF3SO3)2] gave [Os7(CO)17(eta6-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 eta6-C6H6 ligand occupies a site on the central Os4 tetrahedron while in 2 in the eta6-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 eta6-C6H6 ligand in 4 occupies a similar site to that found in 1.