Computational Insights into Malononitrile-Based Carbanions for CO 2 Capture.
Yuqing FuXian SuoZhenzhen YangSheng DaiDe-En JiangPublished in: The journal of physical chemistry. B (2022)
Although anionic N and O sites have been widely used in chemisorption of CO 2 , carbanions are much less explored for CO 2 capture. Here we employ ab initio calculations and quantum mechanical/molecular mechanical (QM/MM) molecular dynamics (MD) simulations to examine the interaction between CO 2 and the malononitrile carbanion, [CH(CN) 2 ] - . We have explored the potential energy surface of CO 2 binding by scanning the C-C distance between CO 2 and the central C site of the carbanion. We find that CO 2 prefers to bind to the nitrile group physically rather than to form a C-C bond via the carboxylation reaction at the sp 2 C site. Moreover, the two -CN groups can attract two CO 2 molecules at equal strength. The presence of an alkali metal ion enhances both physical and chemical interactions of CO 2 with the malononitrile carbanion. QM/MM MD simulations further confirm the preference of physical interaction in the condensed ionic liquid phase with a phosphonium cation. Our findings suggest that ionic liquids based on the malononitrile carbanion may have a high CO 2 solubility for carbon capture.