In-depth DFT insights into the crucial role of hydrogen bonding network in CO2 fixation into propylene oxide promoted by Biomass-Derived deep eutectic solvents

Abstract

The CO2 fixation into epoxide to produce cyclic carbonate is a promising route to realize the large-scale utilization of CO2. In this work, a detailed DFT investigation has been carried out to elucidate the mechanistic details of the CO2 conversion into propylene carbonate (PC) catalyzed by bio-mass derived deep eutectic solvents (bio-DESs), obtained by combining hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA) molecules. Our calculations support the known beneficial effect of hydrogen bonds in activating the epoxide. On the other hand, DFT results also show that hydrogen bonds and transfers do also stabilize the negative charge of determining intermediates, with the consequent undesired effect of reducing the nucleophilicity of the oxygen atom involved in the final ring closure step. Moreover, hydrogen bonds are also established between the HBDs and the PC product, thus hampering its release. Our theoretical results offer an in-depth understanding of the CO2 fixation involving bio-DESs, which can guide towards the development of more efficient bio-catalysts.