Reactivity and\nMechanism of Recoverable Pd<sub>1</sub>@C<sub>3</sub>N<sub>4</sub> Single-Atom Catalyst in Buchwald–Hartwig\nAminations

Buchwald–Hartwig\n(BH) aminations are crucial for synthesizing\narylamine motifs in numerous bioactive molecules and fine chemicals.\nWhile homogeneous palladium complexes can be effective catalysts,\ntheir high costs and environmental impact motivate the search for\nalternative approaches. Heterogeneous palladium single-atom catalysts\n(SAC) offer promising recoverable alternatives in C–C cross-couplings.\nYet their use in C–N couplings remains unexplored, and mechanistic\ninsights into amine coupling with aryl halides over solid surfaces\nthat could guide catalyst design are lacking. Here, we demonstrate\nthat palladium atoms coordinated to well-defined heptazinic cavities\nof graphitic carbon nitride (Pd<sub>1</sub>@C<sub>3</sub>N<sub>4</sub>) deliver practically relevant yields for BH couplings across various\naryl halides and amines, exhibiting persistent activity and negligible\nleaching over several cycles. Notably, Pd<sub>1</sub>@C<sub>3</sub>N<sub>4</sub> shows comparable or superior activity with certain\naryl chlorides to bromides, alongside high chemoselectivity for amines\nover amides. In situ X-ray absorption spectroscopy analyses supported\nby density functional theory simulations identify the concerted role\nof the ligand and the C<sub>3</sub>N<sub>4</sub> host in determining\nthe performance, with a Pd(II) nominal oxidation state observed under\nall coupling conditions. Complementary structural and kinetic studies\nhighlight a distinct reaction mechanism than that typically reported\nfor homogeneous catalysts. These findings offer key insights for designing\nrecyclable SAC for BH coupling, setting the basis for extending the\nscope toward more complex industrial targets.