The mechanisms of the photochemical and thermal rearrangements of [6,5] open fulleroids to the [6,6] closed methanofullerenes and the catalytic effect of electron acceptors

The thermal first-order rearrangement of [6,5] open fulleroids to the corresponding [6,6] closed methanofullerene isomer has been investigated. This thermal first-order rearrangement can be induced to follow a unimolecular pathway at reasonable temperatures if radical stabilizing groups are attached to the one carbon bridge. It appears that these rearrangements involve a biradical intermediate, which achieves some of its radical stabilization from the fullerene cage.; Both the thermal first-order and the photochemical zero-order rearrangements of aryl substituted [6,5] open fulleroids are catalyzed in the presence of some electron acceptors. The catalyzed thermal rearrangement appears to involve a zwitteronic-type intermediate while the catalyzed photochemical isomerization proceeds via an excited state electron transfer process. The photochemical reaction of bis-(-p-methoxyphenyl) fulleroid and tetranitromethane appears to generate an addition product rather than the corresponding [6,6] closed bis-(-p-methoxyphenyl) methanofullerene.; Cyclic voltammetric studies of aryl [6,5] open fulleroids and their corresponding [6,6] closed methanofullerenes demonstrate that the oxidation potential of these aryl substituted C₆₀ derivatives depends on the electron donating abilities of the substitutients. Assuming that the first oxidation leads to the opening of the cyclopropyl ring, we have proposed that both [6,5] open and the [6,6] closed isomers are oxidized to the same radical cation intermediate. If our proposal is correct, then the free energy difference between the [6,5] open and the [6,6] closed isomers is simply the difference in their oxidation potentials and can be electrochemically measured. In all cases studied, the free energy difference is about 5 kcal/mol.