Monitoring of the Pre-Equilibrium Step in the Alkyne Hydration Reaction Catalyzed by Au(III) Complexes: A Computational Study Based on Experimental Evidences.

The coordination ability of the [(ppy)Au(IPr)] fragment [ppy = 2-phenylpyridine, IPr = 1,3-(2,6-di-isopropylphenyl)-imidazol-2-ylidene] towards different anionic and neutral X ligands (X = Cl, BF, OTf, HO, 2-butyne, 3-hexyne) commonly involved in the crucial pre-equilibrium step of the alkyne hydration reaction is computationally investigated to shed light on unexpected experimental observations on its catalytic activity. Experiment reveals that BF and OTf have very similar coordination ability towards [(ppy)Au(IPr)] and slightly less than water, whereas the alkyne complex could not be observed in solution at least at the NMR sensitivity. Due to the steric hindrance/dispersion interaction balance between X and IPr, the [(ppy)Au(IPr)] fragment is computationally found to be much less selective than a model [(ppy)Au(NHC)] (NHC = 1,3-dimethylimidazol-2-ylidene) fragment towards the different ligands, in particular OTf and BF, in agreement with experiment.