Understanding the Reactivity of Ion-Encapsulated Fullerenes

The influence of the encapsulation of an ion inside the C-60 fullerene cage on its exohedral reactivity was explored by means of DFT calculations. To this end, the Diels-Alder reaction between 1,3-cyclohexadiene and M@C-60 (M=Li+, Na+, K+, Be2+, Mg2+, Al3+, and Cl-) was studied and compared to the analogous process involving the parent C-60 fullerene. A significant enhancement of the Diels-Alder reactivity is found for systems having an endohedral cation, whereas a clear decrease in reactivity is observed when an anion is encapsulated in the C-60 cage. The origins of this reactivity trend were quantitatively analyzed in detail by using the activation strain model of reactivity in combination with energy decomposition analysis.