Transformation of methano[60]fullerenes in dihydrofullerofuranes induced by electron transfer

Abstract

The electrochemical reduction of methano[60]fullerenes (61-acetyl-61-(diethoxyphosphoryl)methano-60-fullerene 1, 61-acetyl-61-(diisopropoxyphosphoryl)methano-60-fullerene 2, 61-(2,2-diethoxyacetyl)-61-(diethoxy-phosphoryl)methano-60-fullerene 3, 61-phenyl-61-(1,2-dioxo-3,3-dimethyl-buthyl)methano-60-fullerene 4) in o-dichlorobenzene-DMF (3:1 v/v)/0.1 M Bu 4NBF 4 on a glass–carbon electrode proceeds in a few steps. The reversible transfer of the first electron results in the formation of radical anions registered by ESR method. The subsequent reduction proceeds differently because of the various stability of anionic intermediates. The radical anions of the methanofullerenes 3 and 4 are less stable than the radical anions of compounds 1 and 2 and less stable than the radical anions of methanofullerenes, which contain an ester and/or a phosphonate group. The opening of a cyclopropane ring occurs during the stage of the formation of radical trianions of methanofullerenes 1, 2. The same process for compounds 3, 4 proceeds slowly in radical anions and fast in dianions. The opening of cyclopropane ring for all compounds is not accompanied by the elimination of methanogroup and results in the formation of dihydrofullerenofurane derivatives. The transformation of methanofullerene 3 induced by single electron transfer proceeds via a chain reaction mechanism.