Insights into the Diels–Alder Reaction of [M₃N@I_h-C₈₀]^0/1+ (M = Sc or Y): Effects of Oxidation on the Reactivity and Regioselectivity

Abstract

Diels–Alder (DA) cycloaddition is one important method to generate new derivatives of fullerenes, which is important to accelerating their application. In this study, the DA reaction of 1,3-butadiene and [M3N@I h -C80]0/1+ (M = Sc and Y) has been investigated by density functional theory calculations to further uncover the effects of different metallic clusters and oxidation states on the reactivity and regioselectivity. 5,6-adduct 2 is thermodynamically most favored for M3N@I h -C80 (M = Sc and Y) but is less favorable in Y3N@I h -C80 than in Sc3N@I h -C80, which arises from the large distortion energy of Y3N@I h -C80 in 5,6-adduct 2. Further analyses reveal a correlation between the geometrical change of Y3N and the distortion energy of Y3N@I h -C80. Furthermore, the oxidized endohedral metallofullerenes [M3N@I h -C80]+ (M = Sc or Y) showing electron-withdrawing characteristics showed higher reactivity, lower regioselectivity, and quite a different reaction mechanism as compared with the neutral one. The theoretical results suggest that strain plays a significant role in the reactivity of [Y3N@I h -C80]+. The spin density distribution of the 5,6-bond has a considerable influence on the 5,6-addition but little influence on the 6,6-addition.