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 [Os-6(CO)(18)] with 1.1 equivalents of Me3NO, in CH2Cl2, in the presence of one equivalent of [Au(2)dppm]Cl-2 (dppm = Ph2PCH2PPh2), at room temperature, affords the new mixed-metal cluster [Os-6(CO)(17)(Au(2)dppm)] (1), in high yield. Subsequent reduction of 1 with Na-Hg amalgam, and subsequent treatment with [Ru(eta(5)-C5H5)(MeCN)(3)][PF6] (2) afforded two decanuclear clusters [Os-6(CO)(17)(Au(2)dppm){Ru(eta(5)-C5H5)}(2)] (3) and [Os-6(CO)(16)(Au(2)dppm){Ru(eta(5)-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, H-1- and P-31-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 [Os-6(CO)(18)] is retained and the two Au atoms of the Au(2)dppm group cap one Os-3 face in a mu(3)-eta(2) 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 Au(2)dppm group. One Ru atom caps another face of the Os-5 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. (C) 2000 Elsevier Science S.A. All rights reserved.