Abstract
Diels-Alder cycloaddition reaction is helpful to produce covalent
derivatives of fullerene with desirable electronic and physical
properties. In the present venture, we have computationally investigated
the reactivity of neutral C60 and its
Li+ encapsulated derivative towards Multi-Diels-Alder
(MDA) reaction with 1,3-butadiene, employing density functional theory
(DFT). The computational reports available to date illustrate the
functionalization of fullerene surfaces of neutral and encapsulated
C60 (Ca and Sm) with two butadiene molecules. In this
article, we aim to investigate whether more than two butadiene molecules
can be attached to the fullerene surface or not. To do so, we have shown
that the MDA reaction initiates with the formation of an encounter
complex between the mono-functionalized fullerene product and the second
butadiene molecule. In this context, two different approaches, namely
‘Direct’ and ‘Alternative’ have been considered based on the attachment
of the second butadiene, i.e., whether it is attached to the opposite or
adjacent position of the first functionalization, which eventually
produces the same final product. We have explored the MDA reactions by
considering a total of four diene molecules that can be embedded
successfully on the fullerene surface, with each reaction step having a
high degree of exothermicity, thus making the overall reaction
thermodynamically facile. In harmony with the mono- and
bis-cycloaddition reactions, for MDA reaction also, the positive impact
of Li+ encapsulation for enhancing the reactivity of
fullerene surface towards butadiene attachment is evident from our
study. On-the-fly calculations also suggest the bond preference for
[6, 6] connectivity than its [6, 5] counterpart, to be the
suitable dienophile, just like the mono- and bis-functionalization
reported earlier. Overall, the present study will foresee an extensive
idea about the detailed mechanism of the MDA reaction on neutral
C60 and Li+@C60 that
could encourage the scientists to perform the aforementioned reaction
for other fullerene derivatives in the long run.