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)(AuPPh ₃)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.