The promise of N-heterocyclic carbenes to capture and valorize carbon dioxide

With increasing environmental concerns due to the anthropologic emissions of greenhouse gasses, especially carbon dioxide (CO₂), the development of new technologies to capture the latter is of great public value. While amino-containing materials excel in capturing CO₂, they generally suffer from a few limitations, namely, the high energy penalty for desorption and the obstacle to directly convert CO₂ into valuable resources. In this context, molecular or polymeric compounds based on N-heterocyclic carbenes (NHCs) have emerged as versatile alternatives to efficiently sequester CO₂. NHCs are among the most investigated reactive species in chemistry: not only have they been intensively used as ligands for transition metal catalysts but also they exhibit a rich chemistry, either as true reagents or as organic catalysts. However, their air- and moisture-sensitivity represents a limitation to their use in synthesis. As reviewed thereafter, NHCs can selectively react with CO₂ forming stable adducts, in the form of zwitterionic betaine-type species, providing CO₂ directly-on-site for further fixation. Advances in the use of NHCs in this field are illustrated in this paper with a special emphasis on integration of NHCs in materials enabling heterogeneous utilizations in capture and catalysis.