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 ( K cat / K M ) of 19.3 M –1 s –1, comparable to natural cytochrome c and 264-fold higher than conventional Fe 3 O 4 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 H )-furanone (HFO) under mild conditions. Mechanistic studies, including EPR and DFT calculations, reveal that the catalytic pocket synergistically promotes H 2 O 2 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.