Phosphorylated methano[60]fullerenes containing nitroxyl radicals: synthesis,structures, and electrochemical behavior

Phosphorylated methano60]fullerenes containing one or two nitroxyl radicals were synthesized for the first time. Their structures were established from spectroscopic data and their compositions, by MALDI-TOF mass spectrometry. Their electrochemical reduction in a system o-dichlorobenzene-DMF/0.1 M Bu₄NBF₄ was studied by cyclic voltammetry, preparative electrolysis, and ESR spectroscopy in combination with in situ electrolysis. Both compounds were found to undergo four-step reduction of the fullerene sphere, reduction of nitroxyl, opening of the three-membered ring, and elimination of addends as carbanions stabilized by protonation and rearrangement into phosphate ions and substituted acetylene, which are accompanied by the formation of free fullerene and dihydrofuranofullerene. The rates of the ring opening and the addend elimination increased with an increase in the negative charge on the fullerene sphere. These reactions are fast in the case of transfer of three electrons. With the use of model compounds, heterogeneous electron transfer to the nitroxyl radical at the potentials of the transfer of the third electron to the fullerene sphere and homogeneous intramolecular electron transfer from the dianion of the fullerene sphere were revealed. The mechanisms of the observed transformations are discussed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1594–1607, July, 2005.