Theoretical study on the reaction mechanism of bis-addition of methyl azide to C60 (II)

The processes of 1,3-dipolar cycloaddition (1,3-DC) of methyl azide to azafulleroid (C60NCH3) have been investigated by using AM1 semi-empirical and density functional methods. Based on the charge distributions of the reagents, there are four most possible modes for methyl azide to attack the double bonds of C60NCH3. In each case, N2 extrusion takes place via two steps, which is consequent upon the formation of a triazoline intermediate. The first step is the breaking of a N-N single bond, and the second one undergoes the liberation of a N2 molecule with the simultaneous formation of a new C-N bond. Three bisazafulleroid isomers would be produced through the four reaction paths, one of which has two N atoms bonded to two neighboring open 5-6 junctions of the same pentagon, and the other two have their N atoms bonded to the alternate open 5-6 junctions around the same pentagon and the same hexagon, respectively. Because of the interlacements of their corresponding energy barriers in the rate-controlling steps, interaction energies and the apparent active energies, the four reaction modes will all possibly occur in principle.