Synthesis of heteronuclear gold–rhodium cluster compounds and structural characterisation of [Rh(CNC8H9)3(AuPPh3)5]2+, [Rh(CNC8H9)2(AuPPh3)6(AuCl)2]+ and [Rh(CO)2(AuPPh3)7]2+

Abstract

The NaBH₄ reduction of a mixture of [Au(PPh₃)Cl] and [Rh(CNC₈H₉)₃Cl] leads to a dark red solution containing several Au–Rh cluster compounds, from which [Rh(CNC₈H₉)₃(AuPPh₃)₅]²⁺1 and [Rh(CNC₈H₉)₂(AuPPh₃)₆(AuCl)₂]⁺2 have been isolated. The cluster [Rh(CO)₂(AuPPh₃)₇]²⁺3 has been synthesised by addition of 1 equivalent of [Au(PPh₃)(NO₃)] to the tetrahydrofuran-soluble fraction of a solution obtained by the borohydride reduction of a mixture of [Au(PPh₃)(NO₃)] and [Rh(CO)₂(MeCN)₂]NO₃. Compounds 1 and 3 have been characterised using ³¹P-{¹H} NMR, IR and fast atom bombardment mass spectroscopy and single-crystal X-ray techniques. Since 2 was formed only in low yield it has been characterised only by single-crystal X-ray diffraction methods. The structures of the three compounds are related and may be described as derivatives of a rhodiumcentred Au₁₂ icosahedron formed by removing four, five and seven vertices from the icosahedral cage.