Dicationic Ionic Liquid @MIL-101 for the Cycloaddition of CO2 and Epoxides under Cocatalyst-free Conditions

Dicationic ionic liquid 1,1′-(hexane-1,6-diyl)-bis(3-methylimidazolium) dibromide was synthesized inside an MIL-101 metal–organic framework via a facile ship-in-bottle technique. The resultant dicationic ionic liquid @MIL-101 composite contains Cr sites as a Lewis acidic center and Br– as a nucleophile. The high BET surface area (1162 m2/g) and good synergic effects between the dicationic ionic liquid and MIL-101 resulted in good CO2 sorption capacity (47.4 cm3/g at 273 K) and high catalytic activity for the cycloaddition reaction of CO2 with epoxide without any cocatalyst or solvent, and a 92.5% propylene carbonate yield was obtained under 100 °C, 1.0 MPa for 2.5 h. Moreover, the dicationic ionic liquid @MIL-101 composite also showed better recycling stability and easy separation in the CO2 cycloaddition reaction. Compared with the complex synthetic route for the reported ionic liquid functional metal–organic frameworks, the facilely synthesized dicationic ionic liquid @MIL-101 composite exhibited comparable performance in CO2 capture and utilization.