Halogen-Substituted Zinc Porphyrin-Based Covalent Triazine Frameworks for Efficient Catalytic CO2 Cycloaddition to Aziridines.

The cycloaddition of carbon dioxide (CO2) with aziridines represents a promising approach to produce high-value-added industrial products and offer potential for mitigating CO2-related global warming issues. However, high temperature and/or high pressure are required for traditional thermally driven cycloaddition of CO2 with aziridines by employing so-far reported catalysts, and more efficient catalysts need to be developed for mild procedures. Herein, we construct three zinc porphyrin-based covalent triazine frameworks (ZnDBP-CTFs), including ZnHDBP-CTF and halogen-substituted ZnDBP-CTFs (ZnClDBP-CTF and ZnBrDBP-CTF) at porphyrin meso positions, and investigate their catalytic activity in CO2 cycloaddition to aziridines. Interestingly, different electron-withdrawing halogen atoms in the ZnDBP-CTFs skeleton not only tune the Lewis acidity of the coordinated zinc center but also vary the BET surface area of the materials. Encouragingly, under mild conditions (1 atm CO2, 70°C), the ZnBrDBP-CTF with bromine atoms substituted at meso positions of porphyrin rings exhibits remarkable catalytic performance with the reaction rate reaching 16.35 mol mol-1 h-1, which is among the state-of-the-art cases for catalytic CO2 cycloaddition to aziridines. This study demonstrates that ZnDBP-CTFs can be rationally tuned by incorporating various halogen atoms at the meso positions of the porphyrin units, thereby providing a robust strategy for modulating the catalytic activity of metalloporphyrin-based CTFs.