Reactivity of the mixed-metal cluster [Os-6(CO)(17)(Au(2)dppm)] towards gold electrophiles (dppm = Ph2PCH2PPh2)

Reduction of the mixed-metal octanuclear cluster [Os-6(CO)(17)(Au(2)dppm)] (1) with Na-Hg amalgam and subsequent reaction with one equivalent of [Au(2 )dppm][NO3] affords two isomers of the neutral decanuclear cluster [Os-6(CO )(17)(Au(2)dppm)(2)] (2a, 2b). In a similar reaction between the reduced fo rm of 1 with two equivalents of [AuPPh3][NO3] gives two isomers of the rela ted cluster [Os-6(CO)(17)(Au(2)dppm(2))(AuPPh3)(2)] (3a, 3b). All the new c lusters have been characterised by IR and NMR spectroscopy and FAB mass spe ctrometry. The molecular and crystal structure of 2a has been established b y a single-crystal X-ray structure. In 2a the six Os atoms define an octahe dron, in contrast to the bicapped tetrahedral osmium core previously observ ed for I. Two of the Au atoms in 2a cap adjacent triangular faces of the Os , octahedron while the third spans an open OsAu2 triangle, and the fourth c aps a closed OsAu2 triangle. Overall the decametal core may be viewed as an octahedron fused with a capped square based pyramid. (C) 2000 Elsevier Sci ence B.V. All rights reserved.