ELECTROCHEMISTRY OF MONO-ADDUCTS THROUGH HEXAKIS-ADDUCTS OF C-60

The first systematic electrochemical study by cyclic voltammetry (CV) and rotating-disk electrode (RDE) of the changes in redox properties o f covalent fullerene derivatives (2-11) as a function of increasing nu mber of addends is reported, Dialkynylmethanofullerenes 2-4 undergo mu ltiple, fullerene-centered reduction steps at slightly more negative p otentials than C-60 (1; see Table and Fig. 1). The two C-spheres in th e dumbbell-shaped dimeric fullerene derivative 4 show independent, ide ntical redox characteristics. This highlights the insulating character of the sp(3)-C-atoms in methanofullerenes which prevent through-bond communication of substituent effects from the methane bridge to the fu llerene sphere. In the series of mono- through hexakis-adducts 5-11, f ormed by tether-directed remote functionalization, reductions become i ncreasingly difficult and more irreversible with increasing number of addends (see Table and FiR. 2). Whereas, in 0.1M Bu(4)NPF(6)/CH2Cl2, t he first reduction of mono-adduct 5 occurs reversibly at -1.06 V vs. t he ferrocene/ferricinium couple (Fc/Fc(+)), hexakis-adduct 11 is reduc ed irreversibly only at -1.87 V. Hence, with incremental functionaliza tion of the fullerene. the LUMO of the remaining conjugated framework is raised in energy. Reduction potentials are also dependent on the re lative spatial disposition of the addends on the surface of the fuller ene sphere. Observed UV/VIS spectral changes and changes in the chemic al reactivity along the series 5-11 are in accord with the results of electrochemical measurements. Further, with increasing number of adden ds, the oxidation of derivatives 5-11 becomes more reversible. Whereas oxidations are increasingly Facilitated upon going from mono-adduct 5 (+1.22 V) to tris-adduct 7 (+0.90 V), they occur at nearly the same p otential (+0.95 to +0.99 V) in the higher adducts 8-11. This indicates that the oxidations occur in these compounds at a common sub-structur al element, for which a 'cubic' cyclophane is proposed (see Fig. 3). T his sub-structure is fully developed in hexakis-adduct 11.