Jinkui Zhou, Anton Rieker, Thomas Grösser, Andreas Skiebe and Andreas Hirsch
The electrochemical properties of four singly bridged (1–4) and one doubly bridged (5) N-substituted imino[60]fullerenes have been investigated with cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The substituents on the imino nitrogen are methoxycarbonylmethyl (1, 2, 5), 4-(pentafluorophenoxycarbonyl)phenyl (3), and 4-(succinimidoxycarbonyl)phenyl (4). [6,6]-Bridged structures (2) with closed and [5,6]-bridged structures (1, 3, 5) with open transannular bonds were compared for the first time. Whereas C60 and 1–4 exhibit four successive, reversible reduction peaks in terms of an EEEE mechanism, a chemical reaction followed the cathodic reduction of 5 to 5˙-. This effect is particularly clear in the DPV, where all subsequent reduction peaks were doubled. This can be explained by an ECEEE mechanism, in which 5 after the first E reduction undergoes a chemical transformation into one or two new species, which are further reduced in EEE processes. In the anodic oxidation of 1–5 a two-electron transfer was confirmed. In sharp contrast to all other fullerene derivatives, a quasireversible oxidation of 4 could be observed. To our knowledge, this is the first report of a quasireversible electrochemical oxidation for C60 mono adducts. The reduction potentials exhibit good linear relationships with the calculated LUMO energy levels. Significantly, compared to C60, the reductions of the [6,6]-bridged derivative 2 as well as of the doubly [5,6]-bridged compound 5 occur at more negative potentials, whereas those of the singly [5,6]-bridged compounds 1, 3, 4 are found at less negative potentials.