Phosphorene-Supported Au(I) Fragments as Efficient Heterogeneous Single-Site Catalysts for Hydrofluorination of Alkynes: A Theoretical Investigation

Hydrofluorination of alkynes is an important chemical transformation to afford fluoroalkenes as intermediates for synthesis of pharmaceuticals, peptides, polymers, and agrochemicals. To circumvent the disadvantages of conventional homogeneous protocols and the handling of F-containing chemicals, we proposed that Au(I) fragments dispersed on black phosphorene would be potentially efficient as single-site heterogeneous catalysts for transfer hydrofluorination of alkynes, based on extensive first-principles-based calculations. The catalytic cycle was constructed according to the transfer hydrofluorination of biphenylacetylene with pentafluoropyridine as the fluoroarene using 4-methoxyphenol (4MP) and 4-methoxyaniline (4MA) as nucleophiles over black phosphorene-supported Au(I) fragments. Au(I) fragments are capable of activation of the C–F bonds in fluoroarene via nucleophilic substitution, and activation and conversion of adsorbed alkynes into fluoroalkenes. The calculated free energy barriers are 36.04, 16.67, 15.25, and 20.91 kcal/mol, respectively, when 4MP is used, and are 23.91, 25.85, 10.24, and 34.13 kcal/mol, respectively, when 4MA is used. The elementary step of alkyne hydrofluorination with the highest free energy barrier is determined by the type of nucleophile. Specifically, nucleophilic substitution of fluoroarene for C–F activation is rate-limiting when phenol-type nucleophiles are used, while protodeauration is rate-limiting when aniline-type nucleophiles are used. These Au(I) fragments can be dispersed onto phosphorene by exergonic reactions of known AuNHC complexes. According to the calculated free energy barriers, the performance of these Au(I) fragments in transfer hydrofluorination of alkynes would be comparable to that of reported Au(I) complexes. We expect that these findings may benefit the design and application of heterogeneous single-site Au(I) catalysts for the recycling of fluoro-organics and the selective hydrofluorination of alkynes.