Cyclo[18]carbon Formation from C(18)Br(6) and C18(CO)(6) Precursors

Although cyclo[18]carbon has been isolated experimentally from two precursors, C18Br6 and C-18(CO)(6), no reaction mechanisms have yet been explored. Herein, we provide insight into the mechanism behind debromination and decarbon-ylation. Both neutral precursors demonstrate high activation barriers of similar to 2.3 eV, while the application of an electric field can lower the barriers by 0.1-0.2 eV. The barrier energy of the anion-radicals is found to be significantly lower for C18Br6 compared to C-18(CO)(6), confirming a considerably higher yield of cylco[18] carbon when the C18Br6 precursor is used. Elongation of the C-Br bond in the anion-radical confirms its predissociation condition. Natural bonding orbital analysis shows that the stability of C-Br and C-CO bonds in the anion-radicals is lower compared to their neutral species, indicating a possible higher yield. The applied analysis provides crucial details regarding the reaction yield of cyclo[18]carbon and can serve as a general scheme for tuning reaction conditions for other organic precursors.Funding Agencies|Ministry of Science and Higher Education of the Russian Federation [FSRZ-2020-0008]; Swedish Research Council [2020-04600, 2018-05973]; Swedish National Infrastructure for Computing at the National Supercomputer Centre of Linkoeping University [SNIC 2021-3-22, SNIC 2022-5-103]