The Redox Journey of Iconic Ferrocene: Ferrocenium Dications and Ferrocenate Anions

Abstract

The recent discoveries of both dicationic and monoanionic ferrocene derivatives throw light on the effect of the substituents on the C5 ring as well as the choice of redox agents and solvent system in the preparation of previously believed to be difficult synthetic targets. These oxidized and reduced forms of ferrocene are of interest to spectroscopists, magnetochemists, and theoreticians.

Bis(imidazolium)‐1,3‐diphosphete‐diide: A Building Block for FeC2P2 Complexes and Clusters

“…[12] Ferrocene derivatives, however, can be converted to the dication [13] or monoanion. [14] All redox events mainly involve the iron center supporting a description, in which an Fe n + (n = 1, 2, 3, 4) ion interacts with two Cp À rings. Another way to experimentally probe the electronic effect of a ligand L and the electron density at a metal center, is to investigate complexes, which-apart from L-carry carbonyls as coligands.…”

Preparation and One-Electron Oxidation of Decabromoferrocene

“…Ferrocene can be easily oxidized by mild oxidizers (FeCp 2 0/+ E 1/2 = 0.41 V vs SCE) forming the deep blue ferrocenium cation [Fe III Cp 2 ] + . While numerous ferrocenium compounds have been isolated so far, two-electron oxidations (FeCp 2 +/2+ ) and one-electron reductions (FeCp 2 –/0 ) are hard to achieve due to the extreme redox potentials of these processes. , Changing the substitution pattern allows for a fine-tuning of the electrochemical properties, enabling the isolation of Fe­(IV) and Fe­(I) species. , For instance, while the permethylation of the cyclopentadienyl ligands lowers the first oxidation to E 1/2 = −0.096 V vs SCE, electron-withdrawing groups, e.g., carboxylic or sulfonyl groups, increase the oxidation potentials drastically …”

“…) are hard to achieve due to the extreme redox potentials of these processes. 4,5 Changing the substitution pattern allows for a fine-tuning of the electrochemical properties, enabling the isolation of Fe(IV) and Fe(I) species. 6,7 For instance, while the permethylation of the cyclopentadienyl ligands lowers the first oxidation to E 1/2 = −0.096 V vs SCE, 3 electron-withdrawing groups, e.g., carboxylic or sulfonyl groups, increase the oxidation potentials drastically.…”

Metallocene Anions: From Electrochemical Curiosities to Isolable Complexes

“…[9] Further expansion of the redox chemistry of metallocenes has been a long-standing target for the community. [7,8,10] Derivatized ferrocenium dications with the metal formally in the + IV oxidation state, [Fe(Cp*) 2 ] 2 + (Cp* = C 5 Me 5 ), were recently reported to form under harsh oxidising reaction conditions to extend the redox chemistry of ferrocene derivatives further. [11] However, the chemistry of derivatized metallocene anions, [M(Cp R ) 2 ] À , with the metal in a formal + I oxidation state, has typically lagged behind that of their cationic counterparts.…”

“…Further expansion of the redox chemistry of metallocenes has been a long‐standing target for the community [7,8,10] . Derivatized ferrocenium dications with the metal formally in the +IV oxidation state, [Fe(Cp*) 2 ] 2+ (Cp*=C 5 Me 5 ), were recently reported to form under harsh oxidising reaction conditions to extend the redox chemistry of ferrocene derivatives further [11] .…”