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

Abstract

Treatment of tert-butylamine and benzylamine with [Au(PR′₃)]BF₄ led to the monoauration products [(R′₃P) AuNH₂R]⁺BF₄ ^–(R′= Me, R = Bu^t1a; R′= Me, R = CH₂Ph 1b; R′₃= Ph₂Me, R = Bu^t1c). The salts [{Au(PMe₃)}₃NR]⁺BF₄ ^–(R′= Me, R = Bu^t2a 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)]⁺BF₄ ^–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]⁺BF₄ ^–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.