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

Abstract

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.

Ferrocenyl and pyridyl methylenepyrans as potential precursors of organometallic electron-rich extended bipyrans: Synthesis, characterization and crystal structure

“…On the reverse scan, an irreversible peak appears at À0.76 V. This peak is absent when starting the scan cathodically from E 6 0.20 V. As previously discussed [13], these observations are consistent with the formation of a ferrocenyl radical cation 1 +Á [25], which evolves by dimerization to form a diferrocenylbispyrylium salt 14 (Scheme 7). This was confirmed by electrochemical studies performed on compound 14, obtained by chemical oxidation using ferricinium salt.…”

“…In fact, exocyclic C-C bond lengths lying in the range of 1.39-1.40 Å have been found for push-pull methylene pyran Fischer-type carbene complexes for which, due to the electron withdrawing effect of the carbene fragment, the ground state structure are closed to cyanin limit. [10a,10b,10d] On the other hand, lower values 1.375(5) and 1.352(6) Å) were found for low conjugated symmetrical bis-methylenepyrans [23,13]. Finally, the C 0 2-O2 distance (1.219(4) Å) confirmed the low intermolecular charge transfer between the intracyclic pyran oxygen atom and the aldehyde carbonyl group.…”

“…The data are collated in Table 3. For comparison, values obtained for 1 are also reported [13]. Voltammetric curves are displayed in Supplementary information.…”

“…1A, R = Fc) allowed the reversible formation of diferrocenylbispyrylium salt via a ferrocenylpyran radical intermediate. Subsequent reversible deprotonation of this salt afforded an extended electron-rich diferrocenyl bischalcogenopyran bearing metallocenic group (s) which gave conjugated diferrocenyl bispyrylium salt by subsequent reversible oxidation [13]. Having in mind the development of the solid-state chemistry of extended electron-rich bichalcogenopyrans bearing metallocenic group (s) and pyridyl methylenepyrans.…”

Synthesis, Photophysics and Nonlinear Optical Properties of Stilbenoid Pyrimidine‐Based Dyes Bearing Methylenepyran Donor Groups

“…These anodic potentials should be assigned to the oxidation of the methylenepyran group which probably leads to the formation of dimer byproducts as previously observed for similar derivatives. [22], [24] Interestingly the oxidation potentials of both compounds are quite comparable. This effect should be connected to the equivalent degree of electronic conjugation between the pyran and styrylpyrimidine subunits within both chromophores which is consistent with the equivalent twisted geometries derived from DFT calculations.…”