Rationalizing the Regioselectivity of the Diels-Alder Biscycloaddition of Fullerenes.

The physical factors governing the regioselectivity of the double functionalization of fullerenes have been explored by means of density functional theory calculations. To this end, the second Diels-Alder cycloaddition reactions involving 1,3-butadiene and the parent C60 fullerene as well as the ion-encapsulated system Li+ @C60 have been selected. In agreement with previous experimental findings on related processes, it is found that the cycloaddition reaction, involving either C60 or Li+ @C60 , occurs selectively at specific [6,6]-bonds. The combination of the activation strain model of reactivity and the energy decomposition analysis methods has been applied to gain a quantitative understanding into the markedly different reactivity of the available [6,6]-bonds leading to the observed regioselectivity in the transformation.