Understanding the Exohedral Functionalization of Endohedral Metallofullerenes

Abstract

The endohedral metallofullerenes (EMFs) and their exohedral functionalized derivatives present an increasing attention due to their potential applications in materials science and medicine. However, the current understanding of the reactivity of endohedral metallofullerenes is still very incomplete. In this chapter, we present a thorough study of the Diels-Alder (DA) reactivity of D3h-C78, Sc3N@D3h-C78, Y3N@D3h-C78, Ti2C2@D3h-C78, Sc3N@D5h-C80, Lu3N@D5h-C80, Gd3N@D5hC80„ Sc3N@Ih-C80, Lu3N@Ih-C80-C80, Gd3N@Ih-C80, Y3N@Ih-C80, La2@IhC80, Y3@Ih-C80, Sc3C2@Ih-C80, Sc4C2@Ih-C80, Sc3CH@Ih-C80, Sc3NC@IhC80, Sc4O2@Ih-C80, Sc4O3@Ih-C80, and La@C2v-C82. We have studied both the thermodynamic and the kinetic regioselectivity, taking into account when it was required the free rotation of the metallic cluster inside the fullerene. This systematic investigation was possible only because we use the Frozen Cage Model, which is a low-cost approach to determine the EMF exohedral regioselectivity. Our study has allowed the correction of two wrong experimental assignations of DA adducts, highlighting the key role of computational studies to achieve a deep understanding of exohedral reactivity of the EMFs. The incarceration of the metallic cluster reduces the reactivity of the EMFs respect to the hollow fullerenes. Our results also show that bond distances, pyramidalization angles, LUMOs shape, charge transfer, and cluster volume are the key factors that determine the DA regioselectivity of the fullerenes and EMFs. However, none of them can be used alone to predict which bond will be attacked. Finally, we focus our attention on the essential role of the dispersion interactions to reproduce the experimental results of the exohedral cycloaddition on EMFs.