Cascade\nCO<sub>2</sub> Insertion in Carbanion Ionic\nLiquids Driven by Structure Rearrangement

The CO<sub>2</sub> chemisorption\nin state-of-the-art sorbents based\non oxide/hydroxide/amine moieties is driven by strong chemical bonding\nformation in the carbonate/bicarbonate/carbamate products, which in\nturn leads to high energy input in sorbent regeneration. In addition,\nthe CO<sub>2</sub> uptake capacity was limited by the active sites’\nutilization efficiency, with each active site incorporating one CO<sub>2</sub> molecule or less. In this work, a new concept and generation\nof sorbent was developed to achieve cascade insertion of multiple\nCO<sub>2</sub> molecules by leveraging structure rearrangement as\nthe driving force, leading to in situ generation of extra CO<sub>2</sub>-binding sites and significantly reduced energy input for CO<sub>2</sub> release. The designed ionic liquids (ILs) containing carbanions\nwith conjugated and asymmetric structure, deprotonated (methylsulfonyl)acetonitrile\n([MSA]) anion, allowed the cascade insertion of two CO<sub>2</sub> molecules via consecutive C–C and O–C bond formations.\nThe proton transfer and structure rearrangement of the carboxylic\nacid intermediates played critical roles in stabilizing the first\nintegrated CO<sub>2</sub> and generating extra electron-rich oxygen\nsites for the insertion of the second CO<sub>2</sub>. The structure\nvariation and reaction pathway were confirmed by operando spectroscopy,\nmagnetic resonance spectroscopy (NMR), mass spectroscopy, and computational\nchemistry. The energy input in sorbent regeneration could be further\nreduced by harnessing the phase-changing behavior of the carbanion\nsalts in ether solutions upon reacting with CO<sub>2</sub>, avoiding\nthe energy consumption in heating the solvent. The fundamental insights\nobtained herein provide a promising approach to greatly improve the\nCO<sub>2</sub> sorption performance via sophisticated molecular-scale\nstructural engineering of the sorbents.