A Theoretical Study on the Protodeauration Step of the Gold(I)-Catalyzed Organic Reactions

Density functional theory was used to investigate the protodeauration of organogold compounds, a process which is thought to be the final step in the gold-catalyzed nucleophilic addition to activated π bonds wherein a proton is added and the gold catalyst is regenerated. In this context, we have studied two important factors which control the effectiveness of this transformation. We find that the nature of the alkenyl group in PMe₃Au(alkenyl) affects the reaction barrier through the strength of the Au-C bond; the stronger the Au-C bond, the higher the activation energy. This, in turn, is determined by the π-accepting/donating ability of the substituents on the alkenyl group. We theoretically confirm that, for protodeauration, the reaction should be rapid when π-donating groups are present. In contrast, when π-accepting substituents are present, the intermediate gold complexes may be stable enough to be isolated experimentally. The second important factor controlling the reaction is the nature of the phosphine ligands. We theoretically confirm that electron-rich ligands such as PMe₃ or PPh₃ accelerate the reaction. We find that this is due to the strong electron-donating nature of these ligands, which strengthens the Au-P bond in the final product and thus provides a thermodynamic driving force for the reaction. Also, it is shown how the protodeauration is affected by the number of molecules solvating the proton. The protodeauration mechanism of some other organogold compounds such as gold-alkyl, gold-alkynyl, and gold-allyl species was investigated as well. The findings of this study can be used to design more effective systems for transformations of organogold compounds.