Theoretical study on chemical fixation of carbon dioxide with aziridine into cyclic carbamate catalysed by purine/HI system

Abstract

The cycloaddition of carbon dioxide with aziridine into cyclic carbamate catalysed by purine/HI has been investigated using exchange–correlation functional B3LYP of DFT and the 6-31+G(d,p) basis set for non-iodine atoms and the LANL2DZ for iodine in order to understand the catalytic efficiency of purine/HI system. Two hypothetical reaction mechanisms were proposed for the studied reaction in each catalyst systems. Thermodynamic and kinetic parameters were computed for each step to determine the more favourable route. The calculations reveal that the reaction prefers to proceed through a three-step mechanism in both purine and purine/HI catalyst system. HI plays a co-catalytic role to promote the initial ring-opening of aziridine. The obtained results emphasise purine/HI system had better catalytic efficiency than purine and mechanism II of purine/HI catalysed reaction is more favourable than mechanism I. The more favourable pathway comprises three steps such as ring-opening of aziridine by iodine anion, CO2 insertion and ring-closure. The CO2 insertion step was determined as barrierless. The ring-opening of aziridine was rate-determining step which requires 16.79, 16.33, and 15.94 kcal/mol in the gas phase, water and diethyl ether (better), respectively. Finally, this work endorsed that purine/HI is an effective catalyst for CO2 fixation with aziridine.