Dicationic ionic liquid @MIL-101 for the cycloaddition of CO₂and 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.