Biomimetic Dual-Coordination-Sphere Porphyrin-Based Covalent Organic Frameworks Enable Efficient and Selective Furfural Oxidation

Drawing inspiration from the hierarchical architecture of natural metalloenzymes, we present a biomimetic approach to create an efficient catalyst by engineering both first and second coordination spheres within a covalent organic framework (COF). The catalyst, Fe-TAPP-TT, was synthesized through solvothermal condensation of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP) and thieno[3,2-b]thiophene-2,5-dicarboxaldehyde (TT), followed by iron metallization. In this architecture, the Fe-porphyrin center serves as the primary active site (first coordination sphere), while the sulfur-rich TT linkers form a biomimetic "catalytic pocket" that functions as the second coordination sphere. This dual-coordination environment endows Fe-TAPP-TT with high peroxidase-like activity, exhibiting a catalytic efficiency (Kcat/KM) of 19.3 M-1 s-1, comparable to natural cytochrome c and 264-fold higher than conventional Fe3O4 nanozymes. When applied to the selective oxidation of furfural, a key biomass-derived platform chemical, Fe-TAPP-TT achieved 99.1% conversion with a 53.4% yield of the value-added product 5-hydroxy-2(5H)-furanone (HFO) under mild conditions. Mechanistic studies, including EPR and DFT calculations, reveal that the catalytic pocket synergistically promotes H2O2 activation to generate hydroxyl radicals (•OH) and stabilizes key intermediates, enhancing both catalytic activity and selectivity. This work establishes a strategy for rational design of advanced enzyme mimics and provides an effective catalyst for sustainable chemical transformations.