Reactivity of the mixed-metal cluster [Os6(CO)17(Au2dppm)] towards gold electrophiles (dppm=Ph2PCH2PPh2)

Reduction of the mixed-metal octanuclear cluster [Os6(CO)17(Au2dppm)] (1) with Na–Hg amalgam and subsequent reaction with one equivalent of [Au2dppm][NO3] affords two isomers of the neutral decanuclear cluster [Os6(CO)17(Au2dppm)2] (2a, 2b). In a similar reaction between the reduced form of 1 with two equivalents of [AuPPh3][NO3] gives two isomers of the related cluster [Os6(CO)17(Au2dppm2)(AuPPh3)2] (3a, 3b). All the new clusters have been characterised by IR and NMR spectroscopy and FAB mass spectrometry. The molecular and crystal structure of 2a has been established by a single-crystal X-ray structure. In 2a the six Os atoms define an octahedron, in contrast to the bicapped tetrahedral osmium core previously observed for 1. Two of the Au atoms in 2a cap adjacent triangular faces of the Os6 octahedron while the third spans an open OsAu2 triangle, and the fourth caps a closed OsAu2 triangle. Overall the decametal core may be viewed as an octahedron fused with a capped square based pyramid.