Systematic formation of mixed-metal high-nuclearity clusters: the synthesis and characterisation of [Os6(CO)17(Au2dppm)] and [Os6(CO)17(Au2dppm){Ru(η5-C5H5)}2] (dppm=Ph2PCH2PPh2)

Reaction of the hexaosmium cluster [Os6(CO)18] with 1.1 equivalents of Me3NO, in CH2Cl2, in the presence of one equivalent of [Au2dppm]Cl2 (dppm=Ph2PCH2PPh2), at room temperature, affords the new mixed-metal cluster [Os6(CO)17(Au2dppm)] (1), in high yield. Subsequent reduction of 1 with Na–Hg amalgam, and subsequent treatment with [Ru(η5-C5H5)(MeCN)3][PF6] (2) afforded two decanuclear clusters [Os6(CO)17(Au2dppm){Ru(η5-C5H5)}2] (3) and [Os6(CO)16(Au2dppm){Ru(η5-C5H5)}2] (4) in moderate yield. Cluster 3 loses CO under reflux in toluene to produce 4. The new clusters have been fully characterised by IR, 1H- and 31P-NMR spectroscopies, and mass spectrometry. The molecular and crystal structures of 1 and 3 have been established by single-crystal X-ray analyses. In 1, the bicapped tetrahedral osmium core of [Os6(CO)18] is retained and the two Au atoms of the Au2dppm group cap one Os3 face in a μ3-η2 bonding mode. In 3 the metal core consists of a capped square-based pyramidal arrangement of Os atoms that is capped over the square face by the Au2dppm group. One Ru atom caps another face of the Os5 square-based pyramid, and the second Ru atom caps the Ru atom, two Os atoms and an Au atom to form a trigonal bipyramidal arrangement.