The Nature of Carbon Dioxide in Bare Ionic Liquids.

Ionic liquids (ILs) are among the most studied and promising materials for selective CO capture and transformation. The high CO sorption capacity associated with the possibility to activate this rather stable molecule through stabilization of ionic/radical species or covalent interactions either with the cation or anion has opened new avenues for CO functionalization. However, recent reports have demonstrated that another simpler and plausible pathway is also involved in the sorption/activation of CO by ILs associated with basic anions. Bare ILs or IL solutions contain almost invariable significant amounts of water and through interaction with CO generate carbonates/bicarbonates rather than carbamic acids or amidates. In these cases, the IL acts as a base and not a nucleophile and yields buffer-like solutions that can be used to shift the equilibrium toward acid products in different CO reutilization reactions. In this Minireview, the emergence of IL buffer-like solutions as a new reactivity paradigm in CO capture and activation is described and analyzed critically, mainly through the evaluation of NMR data.