4. Conclusion:
In this article, the MDA reaction on neutral C60 has been computationally explored employing DFT where 6-6 as well as 6-5 bonds are considered. In addition, we have also investigated the effect of Li+ encapsulation on the energetics of each step of the MDA reaction. The consecutive attachments of butadiene molecules on neutral C60 and Li+@C60 commences with the formation of a 1:1 precursor complex between the mono-functionalized fullerene product and a butadiene molecule. In this regard, two possible approaches (’Direct’ and ’Alternative’) have been considered separately, leading to the same tri-functionalized fullerene product after two consecutive additions of butadiene molecules. We have explored the MDA reaction considering the attachment of a total of four diene molecules on the surface of the fullerene cage. Each reaction step shows a high degree of exothermicity, suggesting that the entire reaction is thermodynamically feasible. However, from the PES diagrams, it is evident that Li+ encapsulation makes a positive impact by decreasing the activation barrier and increasing the reaction enthalpy than their neutral counterparts. Thus, we can conclude that MDA reactions become thermodynamically more facile due to Li+ confinement in the C60 cage. Moreover, in the MDA procedure also, the persistence of bond selectivity, i.e., the higher reactivity of [6, 6] bonds over [6, 5], just like mono and bis-functionalization, has been noticed for both C60 and Li+@C60. In a nutshell, the exploration of all possible steps related to MDA reaction on neutral as well as Li+ endohedral C60 will motivate the researchers to investigate more complex reactions related to fullerene chemistry for varied applications.