A mesoporous ionic metal-organic framework decorated by flexible alkyl imidazolium bromide as heterogeneous catalyst for efficient conversion of CO2 to cyclic carbonates

A mesoporous ionic MOF-based catalyst (Br−)C3H7-Imidazolium-MOF-1 for the cycloaddition of CO2 to epoxides (CCE) was synthesized by template-assisted method, and its composite and structure were determined by FT-IR, PXRD, NMR, SEM, TEM, XPS and N2 adsorption. (Br−)C3H7-Imidazolium-MOF-1, is constructed by Zr6O4(OH)4 clusters and linear dicarboxylic acid ligands covalently modified by flexible alkyl imidazolium groups (1-methylene-3-propyl-imidazolium bromide). By the synergistic effect of Zr4+ Lewis acid sites and Br− nucleophiles, (Br−)C3H7-Imidazolium-MOF-1 shown superior catalytic performance for the cycloaddition of CO2 to epichlorohydrin in the absence of any co-catalyst under mild conditions. Small steric hindrance from the flexible imidazolium groups and rapid mass transport of reactants and products in the mesoporous catalyst acted synergistically to promote this process. A firm bond between the imidazolium bromide and the framework of (Br−)C3H7-Imidazolium-MOF-1 made it a recyclable heterogeneous catalyst. Furthermore, several additional coupling reactions were investigated with other epoxides as substrates. (Br−)C3H7-Imidazolium-MOF-1 integrated Lewis acid metal sites and Br− nucleophiles and exhibited efficient catalytic activity for cycloaddition of CO2 to epoxides. [Display omitted] •A mesoporous ionic MOF-based catalyst (Br−)C3H7-Imidazolium-MOF-1 for the cycloaddition of CO2 to epoxides (CCE) was built by template-assisted method.•(Br−)C3H7-Imidazolium-MOF-1 shown superior catalytic performance for the cycloaddition of CO2 to epichlorohydrin in the absence of any co-catalyst under mild conditions.