A room temperature synthesizable zeolitic imidazolium framework catalyst for the solvent-free synthesis of cyclic carbonates

A zinc-based zeolitic imidazolium framework ZIF-71 was synthesized at room temperature and its structural and physical properties were exploited for the CO2-epoxide cycloaddition reactions. ZIF-71 is found to catalyze the synthesis of cyclic carbonates under both high (120 degrees C, co-catalyst free) and low temperature (room temperature, with co-catalyst) conditions with > 99% selectivity. The reaction conditions, turnover frequency (TOF), selectivity, reusability and non-leaching properties of ZIF-71 was compared with that of the earlier reported Zn based ZIFs in this area of CO2 transformation and the results showed that the ZIF-71 reporting here stays along or a step ahead of the previously reported ZIFs. More than 99% selectivity to the final five-membered products was achieved by using ZIF-71 throughout the reactions; thereby the essential criterion of 100% atom economy is well maintained. With its permanent porosity and low leaching, the ZIF-71 catalyst is reusable for more than five times. Finally, a reaction mechanism for the catalytic activity of ZIF-71 was also proposed based on the previous density functional theory (DFT) studies.