Understanding the Reactivity of Ion-Encapsulated Fullerenes.

The influence of the encapsulation of an ion inside the C60 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@C60 (M=Li+ , Na+ , K+ , Be2+ , Mg2+ , Al3+ , and Cl- ) was studied and compared to the analogous process involving the parent C60 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 C60 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.