Palladium-Anchored N-Heterocyclic Carbenes in a Porous Organic Polymer: A Heterogeneous Composite Catalyst for Eco-Friendly C–C Coupling

Abstract

Aggregation-induced catalyst deactivation during the reaction in supported metal catalysts prevails as one of the pitfalls toward their practical implementation. Herein, a homogeneously dispersed palladium-coordinated N-heterocyclic carbene (NHC) was strategically integrated inside a microporous hyper-cross-linked polymer via post-synthesis structural modulation. Successful immobilization of spatially isolated Pd (II) units onto the polymer scaffold yielded highly robust heterogeneous catalysts 120-MI@Pd NHC and 120-EI@Pd NHC, respectively. 120-EI@NHC Pd (4.41 wt % Pd) illustrated a remarkable catalytic potency (yield up to >99%) toward the eco-friendly Suzuki–Miyaura coupling (SMC) reaction at room temperature. The superior catalytic efficiency of 120-EI@Pd NHC is further highlighted from its excellent functionality tolerance over 42 substrates bearing electronic diversity and a turnover frequency value reaching up to 4.97 × 103 h–1 at a very low catalyst dosage of 0.04 mol %. Pertaining to heterogenization, the polymer catalyst could be easily reused with intact catalytic efficiency for at least 10 cycles. The catalytic competence of 120-EI@NHC Pd in terms of scope, scalability, and sustainability advocates its proficiency, while processability was achieved by crafting 3D aerogel monoliths. The conceptual feasibility was further investigated by devising a cup-based nano-reactor with gram-scale product isolation over three catalytic cycles.