Significance of comproportionation reaction in multi-step electrochemical reduction of fullerene C60

Voltammetry at platinum ultramicroelectrode in 1,2-dichlorobenzene shows that for a high concentration of supporting electrolyte, THAPF6, reduction waves 1, 2 and 3 of C60 are of identical height. When supporting electrolyte concentration is lowered, the second and the third wave become lower than the first one. This feature does not agree with simple reduction mechanism under diffusion-migration transport, but supports the model, by Amatore and coworkers, that assumes very fast comproportionation reaction. According to this model, higher-charged fullerene anions are present only in the proximity of the electrode surface, because they react with lower-charged intermediates and are eventually converted to single-charged fullerene anions. Only single-charged anions are transported into the bulk of the solution.