Gilding primary amines: formation of organotris(triphenyl-phosphineaurio)ammonium tetrafluoroborates [(AuPPh3)3NR]+BF4–; crystal structures where R = Butor C6H11

Abstract

Tris(triphenylphosphineaurio)oxonium tetrafluoroborate was found to be a powerful aurating reagent for primary amines RNH₂(R = Me, Et, Prⁿ, Prⁱ, Bu^t, 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)₃NBu^t]⁺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’).