Systematic formation of mixed-metal high-nuclearity clusters: the synthesis and characterisation of [Os 6(CO) 17(Au 2dppm)] and [Os 6(CO) 17(Au 2dppm){Ru(η 5-C 5H 5)} 2] (dppm=Ph 2PCH 2PPh 2)

Abstract

Reaction of the hexaosmium cluster [Os 6(CO) 18] with 1.1 equivalents of Me 3NO, in CH 2Cl 2, in the presence of one equivalent of [Au 2dppm]Cl 2 (dppm=Ph 2PCH 2PPh 2), at room temperature, affords the new mixed-metal cluster [Os 6(CO) 17(Au 2dppm)] ( 1), in high yield. Subsequent reduction of 1 with Na–Hg amalgam, and subsequent treatment with [Ru(η 5-C 5H 5)(MeCN) 3][PF 6] ( 2) afforded two decanuclear clusters [Os 6(CO) 17(Au 2dppm){Ru(η 5-C 5H 5)} 2] ( 3) and [Os 6(CO) 16(Au 2dppm){Ru(η 5-C 5H 5)} 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 [Os 6(CO) 18] is retained and the two Au atoms of the Au 2dppm group cap one Os 3 face in a μ 3-η 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 2dppm 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.