3.1.2 MDA reaction on 6-6 double bond of
Li+@C60:
To check the effect of Li+ encapsulation on MDA
reaction, we have explored all three steps associated with the MDA
reaction on 16-6L. It has been well-established that the
encapsulation of Li+ enhances the reactivity of 6-6
double bond of fullerene towards DA reactions and yields
mono-functionalized fullerene as the first DA product[46 ]. Here, we intend to examine whether
the effectiveness of Li+ encapsulation during MDA
reaction associated with the 6-6 double bonds persists or not. The
second DA reaction originated from
A16-6OL (Figure 3 ) is
observed to be 7.8 kcal/mol more stable than the initial reactants. The
activation barrier associated with the conversion of
A16-6OL to
R16-6OLvia
TS16-6OL is found to be 11.7 kcal/mol,
which is 4.0 kcal/mol lower in energy than its neutral counterpart. The
enthalpy change involves in R16-6OLformation is -29.0 kcal/mol, which is ~1.0 kcal/mol
lower than its R16-6O fabrication. So,
it can be articulated that Li+-encapsulation
successfully enhances the reactivity of encapsulated fullerene towards
the second DA reaction by reducing the activation barrier. As evident
from Figure 3 , the third DA reaction is initiated from
A26-6OL, which is placed at -44.9
kcal/mol on the PES. The activation barrier associated with
TS26-6OL (Figure 2 )
corresponding to R26-6Lformation is
found to be 3.6 kcal/mol lower than the neutral C60analogue. The exothermic nature of this step is also noted from the
associated enthalpy change of -26.9 kcal/mol with respect to
A26-6OL, which is 2.4 kcal/mol lower
than that of neutral C60. For the fourth DA reaction,
the adduct, A36-6L (stabilized at-76.9
kcal/mol on the PES) generates
P46-6Lthrough a transition state,
TS36-6L, with a barrier height 14.6
kcal/mol. The end product, P46-6L is
-101.8kcal/mol downhill than the starting reactant
16-6L, indicating the entire process to be
thermodynamically feasible in nature. In this case, all three steps are
also identified as synchronous processes as the newly formed C-C bonds
between the fullerene surface and diene in the TSs are calculated to be
nearly equal in length.
Thus, from our computational analysis, it is evident that for
Li+@C60, all three steps of MDA
reactions are more likely to occur both kinetically as well as
thermodynamically due to reduced activation barrier and higher
exothermicity than its neutral counterpart. So, it can be inferred that
Li+ encapsulation significantly affects the reactivity
in each step of the 6-6 MDA reaction.