How triazole rings capture carbon dioxide: Energy effects and activation barriers

Abstract

The interest in carbon dioxide (CO2) sorbents is fostered by the global peril of climate warming. Herein, we examine a new class of potential CO2 scavengers, 1,2,3-triazoles, the current-year Nobel Prize winners. Their affinities to CO2 were characterized in terms of reaction energy profiles, nucleophilicities of the respective in-ring nitrogen atoms, and continuous geometry alterations during the course of the chemical reactions. We computationally revealed varying abilities of 1,2,3-triazoles and the triazolide anion to chemically fix CO2 via the carboxamidation mechanism and linked them to electron density distributions over the triazole rings. The triazolide anions in a dilute solution and ion pairs of tetraethylammonium 1,2,3-triazolide exhibit competitive CO2 sorption capacities, whereas neutral 1,2,3-triazoles were confirmed to be quite weak bases. The presence of an excessive electron in the heterocyclic anion enhances the nucleophilicities of the three nitrogen atoms and, therefore, gives rise to a promising CO2 scavenger. The solvation in water strongly fosters carboxamidation (decreases both the activation barrier and the energetic effect) in most cases thanks to the emergence of polar carboxyl moiety. The reported new knowledge is necessary to rationally rate manifold classes of nitrogen-containing heterocyclic compounds for the sake of searching for chemically robust and economically affordable CO2 scavengers.