Diels-Alder Reaction on Free C_(68) Fullerene and Endohedral Sc_3N@C_(68) Fullerene Violating the Isolated Pentagon Rule: Importance of Pentagon Adjacency

摘要

The reaction mechanism and regioselectivity of the Diels-Alder reactions of C_(68) and Sc_3N@C_(68), which violate the isolated pentagon rule, were studied with density functional theory calculations. For C_(68), the [5,5] bond is the most favored thermodynamically, whereas the cycloaddition on the [5,6] bond has the lowest activation energy. Upon encapsulation of the metallic cluster, the exohedral reactivity of Sc_3N@C_(68) is reduced remarkably owing to charge transfer from the cluster to the fullerene cage. The [5,5] bond becomes the most reactive site thermodynamically and kinetically. The bonds around the pentagon adjacency show the highest chemical reactivity, which demonstrates the importance of pentagon adjacency. Furthermore, the viability of Diels-Alder cycloadditions of several dienes and Sc_3N@C_(68) was examined theoretically. o-Quinodimethane is predicted to react with Sc_3N@C_(68) easily, which implies the possibility of using Diels-Alder cycloaddition to functionalize Sc_3N@C_(68).