Cyclo[18]carbon Formation from C18Br6and C18(CO)6Precursors

Abstract

Although cyclo[18]carbon has been isolated experimentally from two precursors, C18Br6and C18(CO)6, no reaction mechanisms have yet been explored. Herein, we provide insight into the mechanism behind debromination and decarbonylation. Both neutral precursors demonstrate high activation barriers of ∼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 C18Br6compared to C18(CO)6, confirming a considerably higher yield of cylco[18]carbon when the C18Br6precursor 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.