The Frozen Cage Model:
A Computationally Low-Cost
Tool for Predicting the Exohedral Regioselectivity of Cycloaddition
Reactions Involving Endohedral Metallofullerenes
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Abstract
Functionalization of endohedral metallofullerenes (EMFs)
is an
active line of research that is important for obtaining nanomaterials
with unique properties that might be used in a variety of fields,
ranging from molecular electronics to biomedical applications. Such
functionalization is commonly achieved by means of cycloaddition reactions.
The scarcity of both experimental and theoretical studies analyzing
the exohedral regioselectivity of cycloaddition reactions involving
EMFs translates into a poor understanding of the EMF reactivity. From
a theoretical point of view, the main obstacle is the high computational
cost associated with this kind of studies. To alleviate the situation,
we propose an approach named the frozen cage model (FCM) based on
single point energy calculations at the optimized geometries of the
empty cage products. The FCM represents a fast and computationally
inexpensive way to perform accurate qualitative predictions of the
exohedral regioselectivity of cycloaddition reactions in EMFs. Analysis
of the Dimroth approximation, the activation strain or distortion/interaction
model, and the noncluster energies in the Diels–Alder cycloaddition
of <i>s-cis</i>-1,3-butadiene to X@<i>D</i><sub>3<i>h</i></sub>-C<sub>78</sub> (X = Ti<sub>2</sub>C<sub>2</sub>, Sc<sub>3</sub>N, and Y<sub>3</sub>N) EMFs provides a justification
of the method