Redox Modulation of the Reactivity and Regioselectivity in Diels–Alder Reaction of Metallofullerene La@C₈₂ with Cyclopentadiene

Abstract

Modulation of the reactivity of metallofullerenes is critical for production of metallofullerene derivatives with desired properties and functionalities. In this study, we investigate the effects of reduction and oxidation on the reactivity and regioselectivity in Diels–Alder reaction of metallofullerene La@C82 by means of density functional theory calculations. Because of the enhanced electron‐deficiency characteristic upon oxidation, the oxidized metallofullerene exhibits higher thermodynamic and kinetic reactivity as compared with neutral La@C82. The regioselectivity in the reaction of La@C82 with cylcopentadiene is remarkably changed after oxidation of the metallofullerene, which is explained in terms of the changes in the geometrical structure and the electronic structure of the metallofullerene. Quantitative analysis based on the activation‐strain model demonstrates that the low activation energy barrier for the reaction of the cation La@C82+ with cyclopentadiene originates from small strain energy and large interaction energy between the reactants. Energy decomposition analysis on the transition states of the reactions reveals that the exchange‐repulsion interaction energy is one of the critical factors that determine the kinetic reactivity of the metallofullerene. This study not only provides new theoretical insights on how to modulate the reactivity of metallofullerenes, but also offers guideline for future experimental synthesis of new metallofullerene derivatives.

Overlooked Effects of La-4f Orbitals in Endohedral Metallofullerenes

“…The higher reactivity when including La-4f orbitals could be easily understood by the reduced electron density of the cage surface (Figure ) because the EMF serve as the electron-deficient dienophile in the DA reaction. This change resembles the recently reported higher reactivity of cationic La@C 82 + than that of the neutral one because of its electron-deficiency characteristic . The with-f calculations also cause the shorter bond lengths of reactive [5,6] bond (i.e., increased double bond character) and closer distance between the Cp and C 82 surface than without-f ones, thus more favoring the reaction.…”

“…This change resembles the recently reported higher reactivity of cationic La@C 82 + than that of the neutral one because of its electron-deficiency characteristic. 91 The with-f calculations also cause the shorter bond lengths of reactive [5,6] bond (i.e., increased double bond character) and closer distance between the Cp and C 82 surface than without-f ones, thus more favoring the reaction.…”

Regioselective Diels–Alder Reactions of C70 Directed by Endohedral Ca and Th Atoms

“…It is known that DA addition of dienes to fullerenes/metallofullerenes usually undergoes a concerted mechanism except for some open-shell fullerenes/metallofullerenes such as Li@C 60 and C 68 . ,, The DA reactions of cyclopentadiene with C 70 , Ca@C 70 , and Th@C 70 also proceed through a concerted mechanism. In the initial stage of the reaction, cyclopentadiene and the fullerene/metallofullerene form a complex intermediate through van der Waals interactions (Figures and ).…”