Highly Porous Metalloporphyrin Covalent Ionic Frameworks with Well-Defined Cooperative Functional Groups as Excellent Catalysts for CO2 Cycloaddition

The development of multifunctional heterogeneous catalysts with high porosity and remarkable catalytic activity still remains a challenge. Herein, four highly porous metalloporphyrin covalent ionic frameworks (CIFs) were synthesized by coupling 5,10,15,20-tetrakis(4-nitrophenyl)porphyrin (TNPP) with 3,8-diamino-6-phenylphenanithridine (NPPN) or 5,5 '-diamino-2,2 '-bipyridine (NBPy) followed by ionization with bromoethane (C2H5Br) or dibromoethane (C2H4Br2) and then metalization with Zn or Co. The resulting CIFs showed high efficiency in catalyzing the cycloaddition of propylene oxide (PO) with CO2 to form propylene carbonate (PC). All of the Zn-containing CIF catalysts were able to catalyze the cycloaddition reaction with a PC yield greater than 97 %. The TNPP/NBPy (CIF2) catalyst ionized with C2H4Br2 and metalized with Zn (Zn-CIF2-C2H4) exhibited the highest catalytic activity among the synthesized catalysts. The high catalytic performance of Zn-CIF2-C2H4 is related to its high porosity (577 m(2) g(-1)), high Br:metal ratio (1:3.89), and excellent synergistic action between the Lewis acidic Zn sites and the nucleophilic Br- ions. Zn-CIF2-C2H4 is sufficiently stable that greater than 94 % PC yield could be obtained even after six cycles. In addition, Zn-CIF2-C2H4 could catalyze the cycloaddition of several other epoxides with CO2. These highly porous materials are promising multifunctional and efficient catalysts for industrially relevant reactions.