Ionic‐Liquid‐Functionalized UiO‐66 Framework: An Experimental and Theoretical Study on the Cycloaddition of CO 2 and Epoxides

A facile approach for modifying the UiO‐66‐NH 2 metal–organic framework by incorporating imidazolium‐based ionic liquids (ILs) to form bifunctional heterogeneous catalysts for the cycloaddition of epoxides to CO 2 is reported. Methylimidazolium‐ and methylbenzimidazolium‐based IL units (ILA and ILB, respectively) were introduced into the pore walls of the UiO‐66‐NH 2 framework through a condensation reaction to generate ILA@U6N and ILB@U6N catalysts, respectively. The resultant heterogeneous catalysts, especially ILA@U6N, exhibited excellent CO 2 adsorption capability, which makes them effective for cycloaddition reactions producing cyclic carbonates under mild reaction conditions in the absence of any cocatalyst or solvent. The significantly enhanced activity of ILA@U6N is attributed to the synergism between the coordinately unsaturated Lewis acidic Zr 4+ centers and Br − ions in the bifunctional heterogeneous catalysts. The size effect of the ILs on coupling between the epoxide and CO 2 was also studied for ILA@U6N and ILB@U6N. A periodic DFT study was performed to provide evidence of possible intermediates, transition states, and pathways, as well as to gain deeper insight into the mechanism of the ILA@U6N‐catalyzed cycloaddition reaction between epichlorohydrin and CO 2 .