Computational Insights into C2 and C4 Insertion Pathways for Fullerene Growth with Stick, Handle, and Horn Intermediates

Abstract The formation and growth mechanisms of fullerenes are extremely complex processes. This study focuses on the specific reaction steps of fullerene growth and, based on theoretical calculations, proposes an alternative pattern of C2 insertion and a specific pattern of C4 insertion for fullerenes. These detailed mechanisms involve classical “stick” and “handle” intermediates as well as newly introduced “horn” intermediates. In this work, mechanisms for the carbon chain migration of “stick” intermediates and the enantiomerization of “horn” intermediates are described, and a mechanism involving the rearrangement of the “horn” intermediates is employed to elucidate the growth of Ih(1812)-C60 into a C62 isomer. This pattern exhibits an energy barrier similar to that of the conventional C2 insertion pattern, suggesting that it may occur during the late stages of fullerene growth. Extending this C2 insertion pattern to fullerene chlorination provides a possible formation pathway for the C2v(tetr)-C62 derivative that has not been captured in situ. Furthermore, this work also investigates the C4 insertion mechanism involving both singlet and triplet states and applies it to explain the formation of C3v(1911)-C64. In this reaction, the isomerization of the C4 carbon chain is the rate-determining step, while its energy barrier is lower than that of the C2 insertion.