Gilding primary amines: formation of organotris(triphenyl-phosphineaurio)ammonium tetrafluoroborates [(AuPPh 3 ) 3 NR] + BF 4 – ; crystal structures where R = Bu t or C 6 H 11

Tris(triphenylphosphineaurio)oxonium tetrafluoroborate was found to be a powerful aurating reagent for primary amines RNH2(R = Me, Et, Prn, Pri, But, cyclohexyl, CH2Ph or Ph). Stable, colourless organotris(triphenylphosphineaurio)ammonium tetrafluoroborates are formed in high yields. The products have been characterized by analytical and spectroscopic data, including 197Au Mössbauer spectroscopy for [(AuPPh3)3NBut]+BF4– and single-crystal X-ray analysis of this compound and that where R = cyclohexyl. The ammonium nitrogen atoms have been located at the centre of a distorted tetrahedron in both cases, with Au–N–Au angles smaller than the tetrahedral value and Au ⋯ Au contacts near 3.0 Å indicating attractive forces between the gold atoms (‘aurophilicity’).