Journal of the American Chemical Society, Vol.120, No.31, 7860-7868, 1998
Redox characteristics of covalent derivatives of the higher fullerenes C-70, C-76, and C-78
The electrochemical properties of covalent derivatives of the:higher fullerenes C-70, C-76, C-2 nu-C-78, and D-3-C-78, bearing bis(alkoxycarbonyl)methano addends, were investigated by cyclic voltammetry (CV) and/ or steady-state voltammetry (SSV). Included in this study were a series of previously prepared mono- to tetrakisadducts of C-70, monoadducts of C-76, and bis- and trisadducts of C-2 nu-C-78 and D-3-C-78 For all compounds, several (up to five) reduction steps and one or two oxidation steps were observed. The reduction steps usually required more energy than the corresponding processes in the parent fullerenes whereas the oxidation steps became facilitated with increasing degree of addition. A notable exception to this trend was the observation that two C-76 monoadducts were more readily reduced than the parent fullerene and one was more difficult to oxidize. The electrochemical properties of C-70 derivatives were found to closely resemble those of C-60 adducts. Constitutional isomers displayed nearly identical redox characteristics. Only the first reduction process is reversible by CV or SSV in the entire series of C-70 adducts whereas the electrochemically generated dianions of some of the derivatives underwent a rapid subsequent chemical reaction. The electrochemistry of covalent adducts of C-76 and C-78 differs substantially-from that of the derivatives of the smaller carbon spheres C-60 and C-70 Among all compounds studied, monoadducts of C-76 are the easiest to be reduced or oxidized and their electrochemically generated multiple anions are much more stable under the conditions of the SSV and CV experiments than those of the adducts of C70 and the C-78 isomers. Several of the electrochemically generated trisanions of the adducts of C-78 isomers underwent rapid chemical reactions. Indeed, a new bisadduct of C-2 nu-C-78, not detected in the regular synthetic mixture, was prepared via electrolysis of a trisadduct. This C-2-symmetrical bisadduct seems to be present as an intermediate during every electrolysis of other bis- and trisadducts of C-2 nu-C-78.
Keywords:ELECTROCHEMICAL PROPERTIES;ELECTRON-TRANSFER;CONFIGURATIONAL DESCRIPTION;ESR CHARACTERIZATION;NEGATIVE POTENTIALS;CYCLIC VOLTAMMETRY;MONO-ADDUCTS;C-60;C-84;CHEMISTRY