Primary amines as nucleation centres for gold clustering, and the structural chemistry of polygold ammonium cations

Treatment of tert-butylamine and benzylamine with [Au(PR′₃)]BF₄ led to the monoauration products [(R′₃P)AuNH₂R]⁺BF₄^- (R′ = Me, R = Bu^t 1a; R′ = Me, R = CH₂Ph 1b; R′₃ = Ph₂Me, R = Bu^t 1c). The salts [{Au(PMe₃)}₃NR]⁺BF₄^- (R′ = Me, R = Bu^t 2a or CH₂Ph 2b) derived from the same amines were obtained using the corresponding oxonium salt [{Au(PMe₃)}₃O]⁺BF₄^-. A diauration product [{Au(PMe₃)}₂NH(CH₂Ph)]⁺BF ₄^- 3 was generated upon slow hydrolytic degradation of 2b in solution. Treatment of NH(SiMe₃)₂ with [{Au(PMe₃)}₃O]⁺BF₄^- afforded both the tris- and tetra-aurated ammonium salts, [{Au(PMe₃)}₃NSiMe₃]⁺BF ₄^- 2c and [{Au(PMe₃)}₄N]⁺BF₄^- 4, depending on the reaction conditions. The cation of 2c is one of the very rare examples of silylammonium species. Compound 4 was also obtained from the oxonium salt and ammonia. All compounds have been characterized through analytical and spectroscopic data. The crystal structure of 1a, 1c and 3 have been determined by X-Ray diffraction methods: 1c is a salt with monomeric gold ammonium cations, but 1a and 3 show supramolecular aggregation of the cations into dimers with short intercationic Au ⋯ Au contacts.