Linear free energy relation of methanofullerene C-61-substituents with cyclic voltammetry: Strong electron withdrawal anomaly

Methanofullerenes with cyano, nitro, and carboxyethyl substituents on C-61 were prepared and characterized. The bis(cyano) methanofullerene shows a first, irreversible, reduction peak at room temperature which is ca 160 mV more positive than the corresponding step in C-60. We report for the first time a comparative study of electron-donating and electron-withdrawing substituents on C-61, using the Hammett sigma(m), which shows that the cyano substituent appears to be more electron-withdrawing than predicted by the Hammett relation, This anomaly could be due to kinetics of a rapid follow-up reaction, periconjugation, or ''conjugation'' through the cyclopropane Walsh orbitals. (C) 1996 Elsevier Science Ltd