CO₂ trapping of selected N‐heterocyclic vinylidenes with an NBO mechanistic scrutiny by DFT

Abstract

Trapping of CO 2 is probed by a set of three N-heterocyclic vinylidene minima, from the azole family, including imidazole (1), 1,2,4-triazole (2), and tetrazole(3), at M06-2X/6-311++G** level of theory. Exothermic adsorption of CO 2 over 1, 2, and 3 gives the initial CO 2 -complex, 1 a , 2 a , and 3 a , with no transition state (TS). Consequently, carbenic π-additions to CO 2 (within 1 a , 2 a , and 3 a ) may give reactant-like, three-membered cyclic TSs, which lead to the exothermic formation of 1 b > 2 b > 3 b . Alternatively, CO 2 intramolecular reactions within 1 a , 2 a , and 3 a may result in the formation of the product-like, fivemembered cyclic TSs, which lead to the endothermic formation of unstable side products 1 c , 2 c, and 3 c , which revert to 1 a , 2 a , and 3 a , respectively. Hence, this manuscript focuses on the main CO 2 trapped products (1 b , 2 b , and 3 b ), and takes advantage of the immense potential of the NBO and AIM data in elucidating their formation provisional mechanisms. Unprecedentedly, contributions of different donor-acceptor interacting orbitals to the formation of each product are assessed on the basis of their second-order perturbation stabilization energy (E 2 ) values.

Capture of CO2by O, S, and Se substituted tripletN‐heterocyclic vinylidenes: a theoretical comparison

“…The distance between oxygen of CO 2 and hydrogen of N–H appears independent of E trp for asymmetric 1 t – 3 t . This is in contrast to our previous articles, wherein the symmetric vinylidene, we observed a direct relationship between the trapping energy and the distance between CO 2 and the carbene as well as the degree of bending of CO 2 15–17,34 . Here, it seems that the size of O, S, Se, and the hydrogen bond formed in the product affects this issue.…”

“…This is in contrast to our previous articles, wherein the symmetric vinylidene, we observed a direct relationship between the trapping energy and the distance between CO 2 and the carbene as well as the degree of bending of CO 2 . [15][16][17]34 Here, it seems that the size of O, S, Se, and…”

“…We have assessed the theoretical capture of CO 2 by N , N ‐dihalo‐imidazoliumvinylidenes. Variations of atomic charges on products are qualitatively and quantitatively justified by their resonance forms and the corresponding NBO donor/acceptor interactions 17 . In this work, we probe effects of O, S, and Se on adsorption of CO 2 .…”

“…Variations of atomic charges on products are qualitatively and quantitatively justified by their resonance forms and the corresponding NBO donor/acceptor interactions. 17 In this work, we probe effects of O, S, and Se on adsorption of CO 2 . In contrast to other reports, and for the first time, we observed the effects of factors such as the asymmetry of the molecule, the number of pairs of electrons in the ring atoms, and also the direction in which CO 2 approaches carbon on conducting reaction path.…”