Reductive Fragmentation of 9,9-Diarylfluorenes. Concurrent Radical Anion and Dianion Cleavage. Electron Apportionment in Radical Ion Fragmentations

Article abstract of DOI:10.1021/ja00239a034

Both Radical anions and dianions of 9,9-diarylfluorenes cleave an aryl ring after reduction by alkali metals or naphtalenide radical anions in ether solvents.The relative amount of cleavage through each intermediate depends on the alkali metal cation, the solvent, and the presence or absence of 18-crown-6-ether.The tendency for dianion cleavage parallels that for disproportionation of radical anions to dianions and neutral hydrocarbons.Radical anion fragmentation is proposed to proceed via heterolytic cleavage in which electron flow is in the direction which offsets the charge distribution in the radical ion.In the present case, this initially affords 9-arylfluorenyl radical and aryl anion, which subsequently indergo electron exchange to form the more stable 9-arylfluorenyl anion and aryl radical.