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.