Electrochemical studies of weak carbon and nitrogen acids: Fluorene and p-cyanoaniline in dimethylformamide

The electrochemical reduction of fluorene and p-cyanoaniline in DMF at a platinum electrode is initially a one-electron process which affords the corresponding readical anions. In the absence of an added proton donor, decomposition of the radical anions occurs by carbonhydrogen bond cleavage to give the conjugate bases of the starting materials; the anions subsequently slowly abstract a proton from the tetraalkylammonium cation of the supporting electrolyte to regenerate the original electroactive species. In the presence of dimethylmalonate, both radical anions rapidly electron transfer to the added proton donor. Neither self-protonation nor protonation by the added donor was observed for either radical anion. In addition to proton abstraction, 9-fluorenyl anion reacts with oxygen to give fluorene and hydroxide ion. Abstraction of a proton from fluorene by the latter species then effects a chain reaction in which 9-fluorenyl anion is the chain-carrying species. Reduction of bifluorenyl occurs with carbon-carbon bond cleavage to give 9-fluorenyl anion as the initial product. Subsequent proton transfer from bifluorenyl to 9-fluorenyl anion then yields the final products, 9-bifluorenyl anion and fluorene, in equimolar amounts.