EXPERIMENTAL AND THEORETICAL STUDIES OF GOLD(I) COMPLEXES AU(L)(+) (L=H20, CO, CO, NH3, C2H4, C3H6, C4H6, C6H6, C6F6)

摘要

Radiative association enhances the formation of Au(C6F6)(+) from bare Au+ ions and hexanfluorobenzene in the low-pressure regime of a Fourier transform ion cyclotron resonance mass spectrometer. Due td the relatively small bond dissociation energy (BDE) of Au+C6F6, this complex can be used as a Versatile precursor for the generation of other Au(L)(+) complexes by ligand-exchange reactions. Ion/molecule reactions employing the bracketing technique provide a relative gold(I) cation affinity scheme for the various ligands L, i.e. C6F6 < H2O < CO < C2H4 < C6H6 < NH3 < C3H6 < C4H6. In addition, for some ligand pairs L/L' both the forward and reverse ligand exchange reactions were observed from which equilibrium data at room temperature were derived. For Au(H2O)(+) Au(CO)(+), AU(NH3)(+), and AU(C2H4)(+) the absolute BDEs are evaluated by means of ab initio MO calculations at the MP2 level of theory, and the following gold(I) cation affinities are obtained: 39 kcal/mol (L = H2O), 50 kcal/mol (CO), 69 kcal/mol (NH3), and 73 kcal/mol (C2H4), respectively. On the basis of a comparison of the experimental and computational findings, the absolute error of the calculated BDEs is estimated to be +/-5 kcal/mol. The unusually high BDE of Au(C2H4)(+) Of ca. 70 kcal/mol is further confirmed by the observation that ethene can replace not only a benzene molecule in Au(C6H6)(+) in a slightly endothermic process but also the covalently bound iodine ligand in AuI+ to yield Au(C2H4)(+), setting a lower limit of 59 kcal/mol for BDE(Au+-C2H4). Finally, the relative gold(I) cation affinity scale is compared to findings for M(L)(+) complexes of other transition metals. [References: 60]