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-C₆H ₅Me)] 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)(CF₃SO ₃)₂] gave [Os₇(CO)₁₇(η⁶-C₆H ₅Me)] 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-C₆H₆ ligand occupies a site on the central Os₄ tetrahedron 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-C₆H₆ ligand in 4 occupies a similar site to that found in 1.