A Complete Guide on the Influence of Metal Clusters in the Diels-Alder Regioselectivity of Ih -C80 Endohedral Metallofullerenes

Abstract

The chemical functionalization of endohedral metallofullerenes (EMFs) arouses considerable interest for the possibility to synthesize new species with potential applications in materials science and medicine. Experimental and theoretical studies on the reactivity of endohedral metallofullerenes are scarce. To improve our understanding of the endohedral metallofullerene reactivity, we have systematically studied with density functional methods the Diels-Alder cycloaddition between s-cis-1,3-butadiene and practically all X@Ih -C80 EMFs synthesized up to date: X = Sc3N, Lu3N, Y3N, La2, Y3, Sc3C2, Sc4C2, Sc3CH, Sc3NC, Sc4O2, and Sc4O3.1,2 We have studied both the thermodynamic and the kinetic regioselectivity, taking into account the free rotation of the metallic cluster inside the fullerene. This systematic study has been made possible through the use of the Frozen Cage Model, a computationally cheap approach to accurately predict the exohedral regioselectivity of cycloaddition reactions in EMFs. Our results show that the reactivity of all metal clusters studied is lower than that of the hollow Ih -C80 cage. Except for the Y3 cluster, the addition takes place predominantly over the [5,6] bond. In many cases, however, a mixture of the two possible regioisomers is predicted. In general, the [6,6] addition is favored in EMFs that have a larger charge transfer from the metal cluster to the cage or have a voluminous metal cluster inside. The present investigation represents the first complete and exhaustive guide on the reactivity of Ih -C80 based EMFs.[Figure 1 here]1. M. Garcia-Borràs, S. Osuna, J.M. Luis, M. Swart, and M. Solà, Chem. Eur. J. 2013, DOI: 10.1002/chem.201302202.2. S. Osuna, R. Valencia, A. Rodríguez-Fortea, M. Swart, M. Solà, J.M. Poblet, Chem. Eur. J. 2012, 18, 8944.