Predicting and Understanding the Reactivity of Aza[60]fullerenes

Abstract

The Diels-Alder reactivity of CNH azafullerene has been explored computationally. The regioselectivity of the process and the factors controlling the reduced reactivity of this system with respect to the parent C fullerene have been analyzed in detail by using the activation strain model of reactivity and the energy decomposition analysis method. It is found that the presence of the nitrogen atom and the CH fragment in the fullerene reduces the interaction between the deformed reactants along the entire reaction coordinate.

Influence of the charge on the reactivity of azafullerenes

“…According to the data in Table 1, the reaction occurs preferentially, both kinetically and specially thermodynamically, on [6,6]-bond 4. Although this contrasts to the neutral C59NH system where bond 3 was found to be the most reactive one, 7 in both cases the most reactive C-C belongs to the six-membered ring where the nitrogen atom is present. It should be however noted that the rest of the bonds exhibit similar activation barriers (∆∆E ‡ < 2 kcal/mol), which suggests that the regioselectivity of process involving C59N + is predicted to be rather low.…”

“…The computed reaction profile for the process involving C59N + and cyclopentadiene resembles those computed for the analogous reaction involving C60 or C59NH ( Figure 2). 7 Therefore, regardless of the bond involved in the process, the [4+2]cycloaddition proceeds concertedly through a relatively synchronous transition state (TS) from an initial van der Waals complex (RC) which lies approximately ca. -12 kcal/mol below the reactants (Table 1).…”

“…To enable possible direct comparison, we have used the same level of theory to that used in our previous studies on the reactivity of the neutral C59NH azafullerene 7 and C60. 18a Geometry optimizations of the molecules were performed without symmetry constraints using the Gaussian03 20 optimizer together with Turbomole 6.0.1 21 energies and gradients at the BP86 22 /def2-SVP 23 level of theory using the D3 dispersion correction suggested by Grimme et al 24 and the resolution-ofidentity (RI) approximation.…”

“…2c,6 As expected, the reactivity of these systems is also significantly affected. Indeed, we recently found that the parent azafullenere C59NH is comparatively less reactive than C60 in its Diels-Alder cycloaddition reaction with cyclopentadiene, 7 a process typically used to produce novel fullerene derivatives with tunable properties. 8,9 By means of the so-called Activation Strain Model (ASM) 10 of reactivity in combination with the Energy Decomposition Analysis (EDA) method, 11 this lower reactivity was ascribed to a much weaker interaction between the reactants along the entire reaction coordinate mainly as a result of a weaker (diene)*(fullerene) interaction.…”

“…17 The isolation and/or detection of these charged azafullerenes prompted us to explore their not very well understood reactivity in comparison to our previous study on the reactivity of the parent neutral C59NH system. 7 Therefore, herein we report a detailed investigation on the influence of the charge on the Diels-Alder reactivity of azafullerenes which is based on the application of the ASM-EDA approach, a method which has proven to be extremely useful to our current understanding of the reactivity of fullerenes 7,18 and strongly related systems. 19…”