Bridging the Gap: Heterogeneous Micro-Confined Palladium Catalysts Surpassing Homogeneous Systems for C-N Cross-Coupling in Water.

Homogeneous systems, while highly active, are inherently fragile and prone to catalyst deactivation through metal aggregation, ligand dissociation, and irreversible formation of catalytically inactive palladium black, thereby limiting recyclability during cross-coupling. In contrast, supported heterogeneous catalysts often sacrifice reactivity due to restricted site accessibility, perturbed electronic environments, and uncontrolled metal leaching. Overcoming this dichotomy requires control over palladium speciation under turnover conditions, an objective that remains unmet for C─N cross-coupling. Herein, we report a heterogeneous palladium catalyst embedded in micro-confined spaces to resolve this long-standing limitation and establish a new paradigm for C─N cross-coupling. A hydrophobic confined environment provided by a hyper-crosslinked polymer integrated with t-BuXPhos, and the system selectively stabilises catalytically competent low-valent Pd while suppressing aggregation, ligand dissociation, and metal leaching. Interestingly, this confinement preserves substrate accessibility via dynamic exchange at the material-water interface with the synergy of a non-ionic surfactant CNSL-1000-M, enabling C─N coupling at parts-per-million (ppm) palladium loadings. Our catalyst operating at ≤500 ppm exhibits initial rates up to 31-fold higher than its homogeneous analogue. We have demonstrated the recyclability over five successive cycles, affording a cumulative turnover number (TON) of 2.2 × 104, the highest value reported to date for heterogeneous C─N cross-coupling.