Diferrocenylbispyrylium Salts and Electron-Rich Diferrocenylbispyran from Oxidative Coupling of Ferrocenylpyran. Induced Electron Transfer C−C Bond Making/Breaking Involving a Metallocenyl Radical Intermediate

Electrochemical or chemical dimerization of electron-rich ferrocenylmethylenepyran 1 gave the first dimetallocenylbispyrylium salt 2 known today, through a reverse process that implies reductive C−C bond breaking. Deprotonation of the bispyrylium salt 2 afforded extended electron-rich diferrocenyl bispyran 3, which was subsequently reversibly oxidized to diferrocenyl bispyrylium salt 4. This study constitutes a new system in which two ox/red sequences of different nature were separated by proton/deprotonation steps.