Retro-Bingel reaction in the electrochemical reduction of bis(dialkoxyphosphoryl)methanofullerenes

Four steps of reduction were detected for bis(diethoxyphosphoryl)- and bis(diisopropoxyphosphoryl)methano[60]fullerenes (1, 2) and bis(dietlioxyphosphoryl)methano[70]fullerene (3) by cyclic voltammetry in the o-dichlorobenzene-DMF (3 : 1, v/v)/Bu4NBF4 (0.1 mol L-1) system on a glass-carbon electrode. At the first step the reversible transfer of one electron affords stable radical anions 1 and 2 (g = 1.9999, DeltaH = 1.9 G). When two electrons per molecule are transferred, the methano fragment is rapidly eliminated (retro-Bingel reaction). This process involves the step-by-step cleavage of two C-C bonds of exo-carbon with the fullerene shell in combination with the stepwise transfer of other two electrons and a proton to form finally the carbanion of the methano fragment and fullerene dianion. For all Studied compounds, the elimination rate is much higher than that for bis(alkoxycarbonyl)-and dialkoxyphosphoryl(alkoxycarbonyl)methano[60]fullerenes, which makes it possible to propose bisphosphorylmethane groups as protective in synthesis of new fullerene derivatives.