Synthesis and characterization of (trifluoromethyl)gold complexes

Article abstract of DOI:10.1021/om00108a021

The synthesis of (CF₃)AuL (L = PMe₃, PEt₃, PPh₃) from LAuCl and Cd(CF₃)₂·DME is described. These linear gold(I) compounds readily add excess halogen to form the predominantly trans square-planar gold(III) dihalides (CF₃)AuX₂(L) (X = Br, I). The use of stoichiometric (or less) halogen leads to a significant quantity of (CF₃)₂AuX(L) (L = PMe₃, PEt₃) which is shown to arise from trifluoromethyl/halogen ligand exchange between (CF₃)AuL and (CF₃)AuX₂(L). No evidence for ligand exchange is found when L = PPh₃. (CF₃)₂AuI(L) (L = PMe₃, PEt₃) may also be prepared in 80% yield from the oxidative addition of trifluoromethyl iodide to (CF₃)AuL; experiments with the radical scavenger galvinoxyl suggest a radical chain mechanism for this CF₃I addition. Close examination of the ¹H and ¹⁹F NMR spectra for the new square-planar complexes reveals that downfield shifts occur for both nuclei when a cis halide is changed from Br to I; a trans halide causes an upfield shift upon this substitution. The cadmium reagent is, in general, ineffective for the preparation of Au(III) complexes since reduction to (CF₃)AuL usually occurs. However, treatment of (CF₃)₂AuI(PMe₃) with Cd(CF₃)₂·DME in the presence of excess CF₃I leads to the high-yield synthesis of the tris(trifluoromethyl) species (CF₃)₃AuPMe₃.