A fulleropyrrolidine binitroxide: synthesis, EPR and electrochemical features

Abstract

The synthesis, electrochemical characterization and EPR study of a fulleropyrrolidine monoadduct, bearing two TEMPO groups differently linked at positions 2 and 5 of the pyrrolidine ring, are presented. The exchange interaction J between the two unpaired nitroxide electrons is of the same order of magnitude of the ¹⁴N hyperfine coupling (a_N). EPR investigation in three different solvents showed that J decreases as the temperature increases. Chemical or electrochemical reduction produces a stable triradical anion that, in the case of chemical reduction, was characterized ia EPR spectroscopy. Further chemical reduction produces an unstable species probably corresponding to a protonated compound. The electrochemical study highlights an interesting effect of the fullerene moiety on the kinetics of TEMPO-centered electrochemical reduction, which was analyzed in the frame of Marcus theory of heterogeneous electron transfer.