Reactions of [NEt4][10-endo-{Au(PPh3)}-nido-7,8-C2B9H9Me2]: carbaborane cage transfer from gold to rhodium

Abstract

The reagent [NEt₄][10-endo-{Au(PPh₃)}-nido-7,8-C₂B₉H₉Me₂] has been prepared, and used to synthesise several mixed-metal complexes in which gold atoms are bonded to rhodium. Thus treatment of the gold salt with trans-[RhCl(CO)(PPh₃)₂] or [Rh₂(µ-Cl)₂(CO)₄] in thf (tetrahydrofuran), in the presence of TIBF₄, affords the complexes [RhAu(CO)(PPh₃)L(η⁵-7,8-C₂B₉H₉Me₂)](L = PPh₃ or CO), respectively. Reaction of the gold species with [RhCl(PPh₃)₃] gives the complex [exo-5,10-{Rh(PPh₃)₂}-5,10-(µ-H)₂-10-endo-{Au(PPh₃)}-nido-7,8-C₂B₉H₇Me₂], the structure of which has been established by X-ray diffraction. The latter complex in solution exists in equilibrium with a minor isomer [RhAu(PPh₃)₃(η⁵-7,8-C₂B₉H₉Me₂)] containing a closo-3,1,2-RhC₂B₉ cage system. With the rhodium complex [Rh(cod)(PPh₃)₂][PF₆](cod = cycloocta-1,5-diene), and in the presence of molecular hydrogen, the gold reagent yields a chromatographically separable mixture of [exo-5,10-{Rh(PPh₃)₂}-5,10-(µ-H)₂-10-endo-{Au(PPh₃)}-nido-7,8-C₂B₉H₇Me₂] and [RhAu₂(µ-H)(PPh₃)₃(η⁵-7,8-C₂B₉H₉Me₂)]. A single-crystal X-Ray diffraction study has established the structure of the rhodium–digold compound. The NMR data (¹H, ¹³C-{¹H}, ³¹P-{¹H} and ¹¹B-{¹H}) for the new compounds are reported and discussed in relation to their structures.