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.