Allyl functionalized UiO-66 metal-organic framework as a catalyst for the synthesis of cyclic carbonates by CO₂ cycloaddition

The conversion of epoxides to cyclic carbonates is one of the most common CO₂ fixation reactions. Metal-organic frameworks (MOFs), due to their porosity, easily tunable properties and Lewis acidic sites, are extensively used in heterogeneous catalysis. In this paper, we report the derivatization of the metal-organic framework (MOF) UiO-66 (University of Oslo) with allyloxy groups to give UiO-66-BAT (BAT = bisallyloxyterephthalate). The catalyst was characterized by PXRD, BET, IR, SEM, digestion NMR and CO₂ adsorption. UiO-66-BAT had a good CO₂ uptake of 84 cc/g at 273K and a Qst value of 27.5 kJ mol⁻¹. Due to the affinity of the allyloxy group toward CO₂ and the proximity of the zirconium Lewis acid sites, we applied UiO-66-BAT as a catalyst for the conversion of epoxides to cyclic carbonates by using CO₂. We showed that UiO-66-BAT converts propylene oxide (PO) to its corresponding cyclic carbonates at 50 °C, a 5 bar pressure, and a 6 h reaction time with a 95% yield. UiO-66-BAT also gave a good yield in the conversion of numerous aliphatic and aromatic epoxides. The catalysts exhibited a good recyclability for up to 9 cycles.