Ammonium-, Phosphonium- and Sulfonium-Based 2-Cyanopyrrolidines for Carbon Dioxide Fixation

TL;DR

This study explores ammonium, phosphonium, and sulfonium-based 2-cyanopyrrolidines as potential CO2 scavengers, analyzing their thermochemistry and stabilization mechanisms to improve environmentally friendly carbon capture technologies.

Contribution

It introduces a detailed computational analysis of RTILs with different cations for CO2 fixation, highlighting the role of electrostatic attraction and steric effects in chemisorption.

Findings

Thermodynamically favorable CO2 fixation mechanisms identified.

Intramolecular electrostatic attraction stabilizes zwitterionic products.

Differences in chemisorption performance linked to steric hindrance and nucleophilicity.

Abstract

The development of carbon dioxide (CO2) scavengers is an acute problem nowadays because of the global warming problem. Many groups around the globe intensively develop new greenhouse gas scavengers. Room-temperature ionic liquids (RTILs) are seen as a proper starting point to synthesize more environmentally friendly and high-performance sorbents. Aprotic heterocyclic anions (AHA) represent excellent agents for carbon capture and storage technologies. In the present work, we investigate RTILs in which both the weakly coordinating cation and AHA bind CO2. The ammonium-, phosphonium- and sulfonium-based 2-cyanopyrrolidines were investigated using the state-of-the-art method to describe the thermochemistry of the CO2 fixation reactions. The infrared spectra, electronic and structural properties were simulated at the hybrid density functional level of theory to characterize the reactants and products of the chemisorption reactions. We conclude that the proposed CO2 capturing mechanism is thermodynamically allowed and discuss the difference between different families of RTILs. Quite unusually, the intramolecular electrostatic attraction plays an essential role in stabilizing the zwitterionic products of the CO2 chemisorption. The difference of chemisorption performance between the families of RTILs is linked to sterical hindrances and nucleophilicities of the {\alpha}- and \b{eta}-carbon atoms of the aprotic cations. Our results are supported by the previous experimental CO2 sorption measurements and systematically extend their scope.