3.2.4 MDA reaction on 6-5 double bond of
Li+@C60:
The energy release associated with
A16-5SL formation is calculated to be
6.6 kcal/mol, which is comparable to its ‘Direct’ counterpart
(Figure S4 ).The barrier height
(TS16-5SL) corresponding to
R15-6SL formation is 6.0 kcal/mol
lower than its neutral counterpart. The associated enthalpy change
(-19.8 kcal/mol) suggests the second functionalization on
16-5Lto be exothermic in nature and thus
thermodynamically facile. The third DA reaction has been initiated from
A26-5SL, which eventually generates
R26-5L.The associated activation
height (TS26-5SL) is noted to be 8.2
kcal/mol lower than its uncharged analogue. The exothermic nature of the
third DA step is also noted from its corresponding enthalpy change
(-12.9 kcal/mol). The fourth functionalization follows a similar
mechanism to the one proposed for the ‘Direct’ pathway.
Unlike the ‘Direct’pathway, the asynchronicity arises in the second DA
reaction and becomes more prominent in the third and fourth DA
reactions. The difference of lengths between the two newly forming C-C
bonds in the TS is 0.6 Å for the second TS, which enhances to
~ 1.0 Å for both third and fourth TSs.
In short, it can be easily articulated that Li+encapsulation does affect the reactivity in each step of 6-6 as well as
6-5 MDA reaction irrespective of the approaches considered, i.e.,
whether ‘Direct’ or ‘Alternative’ approach.