Bingel–Hirsch Addition on Endohedral Metallofullerenes: Kinetic Versus Thermodynamic Control

Abstract

An extensive theoretical study of the Bingel-Hirsch addition of bromomalonate on scandium nitride endohedral fullerenes has been carried out. The prototypical and highly symmetrical Sc3N@I(h)-C80, with a structure that satisfies the isolated pentagon rule (IPR), and the non-IPR Sc3N@D3(6140)-C68 fullerene show analogous reaction paths despite the distinct topology of the carbon networks and different rotation freedom of the internal nitride cluster. For the two metallofullerenes, our results predict that the reaction takes place under kinetic control yielding open-cage fulleroids on [6,6] bonds, which is in good agreement with experimental data. The theoretical studies also show that predicting the reactivity of endohedral metallofullerenes is not straightforward and often an accurate analysis of the potential energy surface is required.

The Regioselectivity of Bingel–Hirsch Cycloadditions on Isolated Pentagon Rule Endohedral Metallofullerenes

“…Thebarriers for the interconversion of the different orientational isomers of malonate are very low and accessible at room temperature. [9] In addition, the differences in relative stabilities between different conformers are quite low (see Table S5 in the Supporting Information). Thec omputed intermediates are about 3.5-11.8 kcal mol À1 higher in Gibbs energy than isolated reactants as ar esult of entropic effects (see Tables S3 and S4 in the Supporting Information).…”

“…This addition is ab arrierless process. [9] Afterwards,t he carbanion displaces the bromide and an intramolecular cyclopropane ring closure takes place.…”

“…[10] However, Alegret et al found that BH additions are usually kinetically controlled, thus leading to the kinetic products instead of the most stable ones. [9] Herein, we study the BH addition to all non-equivalent bonds of Sc 3 N@D 3h -C 78 using DFT calculations (see the Supporting Information for computational details). Based on these results and the subsequent analysis we introduce ap ractical and simple guide to predict the most suitable BH addition sites.A ss hown later, this guide only requires as imple evaluation of the EMF cage structure.W ea lso performed the BH cycloaddition for the first time on the unexplored D 5h isomer of Sc 3 N@C 80 ,a nd the synthesis and characterization of the resulting derivatives are described herein.…”

“…Application of the PACt ot he BH addition to Sc 3 N@I h -C 80 predicts that the [6,6] bond is the most reactive in complete agreement with experimental and theoretical studies. [9] We also used the PACt op redict the preferred BH additions to the challenging Sc 3 N@D 5h -C 80 .T his C 80 isomer exhibits nine non-equivalent bonds (five are [6,6] bonds and four [5,6]), and the cluster unit can freely rotate inside. [3] Among all nine possible additions,f ive (out of nine) bonds can be immediately discarded by just applying the PAC.…”

Reactivity differences of Sc3N@C2n (2n = 68 and 80). Synthesis of the first methanofullerene derivatives of Sc3N@D5h-C80

“…2). 33,34 Sc 3 N@D 3 -C 68 possesses eight different types of [6,6]-bonds, nine different types of [5,6]-bonds and one type of [5,5]-bond (Fig. S5-S11, ESI †).…”