Computational insights into themulti‐Diels–Alderreactions of neutralC60and its Li+encapsulated analogue: A density functional theory study

Abstract

AbstractThe exohedral functionalization of encapsulated fullerenes (such as Diels–Alder reaction) gives rise to wide‐ranging derivatives that are useful for potential applications. Though the oligo‐adducts have significant uses in material and biological sciences, they are hardly investigated due to experimental limitations. To shed light on that unexplored area, we have computationally investigated the sequential Diels–Alder reactions, that is, multi‐Diels–Alder (MDA) reaction of neutral C60and its Li+‐encapsulated derivative with 1,3‐butadiene in the present venture employing density functional theory. The computational reports available to date illustrate that the reactivity of neutral C60can be significantly stimulated by the encapsulation of alkali/alkaline earth metal atoms/ions within the fullerene cage. However, the effect of encapsulation has been examined for the Diels–Alder reaction of fullerene derivatives up to bis‐functionalization. Therefore, in the present study, we aim to investigate the kinetic and thermodynamic feasibility of multiple butadiene attachments (beyond two) to the neutral C60surface and also the impact of Li+encapsulation on the reaction mentioned above. 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 depending on the second butadiene attachment to check whether the first functionalization makes the rest of the double bonds in‐equivalent toward the second butadiene addition or not. Each of the reaction steps following these two approaches eventually forms the same tetra‐functionalized final product with a high degree of exothermicity value, thus making the overall reaction thermodynamically facile. The positive impact of Li+encapsulation is well‐understood from the diminished activation barrier and more negative exothermicity value compared to neutral C60in each step of the MDA procedure. Moreover, just like the mono‐ and bis‐functionalization reported earlier, the regio‐selectivity is also retained in the MDA procedure. Overall, the present study will foresee an extensive idea about the detailed mechanism of the MDA reactions on neutral C60and its Li+encapsulated analogue, which will be helpful for further progress in the field of fullerene chemistry.