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-<i>b</i>]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 (<i>K</i>_cat/<i>K</i>_M) of 19.3 M^-1 s^-1, comparable to natural cytochrome <i>c</i> 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(5<i>H</i>)-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.