Efficacy of carbenes for CO2 chemical fixation and activation by their superbasicity/alcohol: a DFT study

DFT calculations predicted a highly efficient binary system consisting of acyclic or cyclic carbenes and alkylcarbonic acids for an efficient CO2 capture process. The driving force for such processes seems to be governed by the pK(a) of the base used. The calculated results suggest that the carbenes possess a much higher pK(a) compared to the superbases DBU and TBD used in earlier studies. The activation barriers computed for the formation of alkylcarbonate salt with the carbene superbases are also favourable compared to the nitrogen bases reported in the literature. The propylcarbonate salt formation is energetically more preferred with these carbenes than their direct CO2 zwitterionic adduct formation. The steric and electronic effects of such carbenes also play an important role towards the determination of the mode of CO2 capture.