Quantitative Evaluation of the Stability of gem-Diaurated Species in Reactions with Nucleophiles

The reactivity of diaurated species toward nucleophiles was investigated. The reaction yields vinyl gold species and is described as simple S(N)2 ligand exchange at gold. Using suitably strong nucleophiles, equilibrium constants were determined to measure the stability of various diaurated species. On the basis of these equilibrium constants the influence of ligand and the nature of vinyl cores on the stability were analyzed. These results have direct implication for gold catalysis: it was demonstrated that vinyl gold intermediates bind the catalytic LAu+ species generally stronger than an alkyne (the substrate) by a factor of 10(6)-10(9). This demonstrates that the formation of diaurated species from vinyl gold intermediates is thermodynamically favored in a catalytic reaction.