Amide-Linked Fluorene Polymer Networks with Polymerization-Induced Palladium Incorporation for Sustainable Aqueous C–C Cross-Coupling

Abstract Amide-linked fluorene polymer networks, structurally related to covalent organic polymers (COPs), are attractive platforms for sustainable heterogeneous catalysis owing to their chemical robustness, structural tunability, and ability to stabilize metal species within organic microenvironments. Herein, we report a fluorene-based amide-linked polymer network (FCOP) obtained through nucleophilic acyl substitution between 9,9-bis(4-aminophenyl)fluorene (FDA) and trimesoyl chloride (TMC) under mild conditions. Two palladium incorporation strategies were investigated: conventional post-synthetic loading (Pd@FCOP-A) and polymerization-induced in situ incorporation during framework formation (Pd@FCOP-B). Solid-state NMR, FT-IR, XPS, BET, SEM, TEM, TGA, and ICP-MS confirmed the formation of a robust amide-rich network and successful Pd incorporation. TEM and ICP-MS analyses revealed that Pd@FCOP-B, despite its lower Pd loading, exhibited higher metal dispersion, markedly reduced leaching, and superior recyclability compared to the post-synthetically loaded analog. Both catalysts promote Suzuki–Miyaura cross-coupling in EtOH/H2O, achieving quantitative conversion within 15 min at 60 °C and high conversions at room temperature. Pd@FCOP-B also enables ligand-free Heck and copper-free Sonogashira reactions, demonstrating broader catalytic versatility. A CHEM21 assessment quantifies this advantage: 0.0056 mol % Pd, a turnover number of 1.76 × 104, and an E-factor of 3.8 excluding the benign EtOH/H2O medium. Computational modeling suggests that cyclic FCOP cavities can stabilize Pd(OAc)2 more effectively than a folded-open oligomeric model, providing a qualitative trend consistent with a confinement-driven stabilization hypothesis and with the TEM observations. These results establish polymerization-induced palladium incorporation as a practical strategy for sustainable C–C cross-coupling through low Pd usage, aqueous reaction media, high catalytic efficiency, and improved catalyst reuse.