Polysubstituted ferrocenes as tunable redox mediators

Abstract

A series of four ferrocenyl ester compounds, 1-methoxycarbonyl- (1), 1,1’-bis(methoxycarbonyl)- (2), 1,1’,3-tris(methoxycarbonyl)- (3) and 1,1’,3,3’-tetrakis(methoxycarbonyl)ferrocene (4), has been studied with respect to their potential use as redox mediators. The impact of the number and position of ester groups present in 1–4 on the electrochemical potential E 1/2 is correlated with the sum of Hammett constants. The 1/1 +–4/4 + redox couples are chemically stable under the conditions of electrolysis as demonstrated by IR and UV–vis spectroelectrochemical methods. The energies of the C=O stretching vibrations of the ester moieties and the energies of the UV–vis absorptions of 1–4 and 1 +–4 + correlate with the number of ester groups. Paramagnetic 1H NMR redox titration experiments give access to the chemical shifts of 1 +–4 + and underline the fast electron self-exchange of the ferrocene/ferrocenium redox couples, required for rapid redox mediation in organic electrosynthesis.

Recent advances on ferrocene-based photoinitiating systems

“…Ferrocene which is a metallocene discovered in 1951 is characterized by a reversible one-electron oxidation process at potential lower than 0.5 V so that ferrocene can be combined with numerous photoinitiators. [165][166][167][168][169][170][171][172] This metal complex is extensively used in electrochemistry as a reference compound for calibration. Considering its low oxidation potential, ferrocene is also an excellent electron-donating group so that numerous push-pull dyes were designed with this iron (II) complex.…”

Extremely Electron‐Poor Bis(diarylmethylium)‐Substituted Ferrocenes and the First Peroxoferrocenophane

“…It could nevertheless be observed as a broad square-wave peak at 1640 mV (1b 2+ ) or 1870 mV (1c 2+ ) in liquid SO 2 , using NBu 4 BAr F24 as the supporting electrolyte ( Figure 6, right). With such positive redox potentials, 1b 2+ and 1c 2+ seem to be the electron-poorest ferrocenes reported to date, including other multiacceptor-substituted ferrocenes such as 1,1Ј-dicyanoferrocene (E 1/2 = 865 mV), 1,1Ј,2,2Ј,4,4Ј-and 1,1Ј,2,2Ј,3,3Ј-hexakis(pentafluorophenylferrocene) (E 1/2 = 940 mV and 951 mV, respectively), 1,1Ј,3,3Ј-tetra(methoxycarbonyl)ferrocene (E 1/2 = 900 mV) [16] and even 1,1Ј,2,2Ј-tetraformylferrocene (E 1/2 0/+ = 1145 mV). [17] In fact, their E 1/2 values nearly match or even surpass that of 1710 mV for the second oxidation of parent ferrocene (i.e.…”

Asymmetric synthesis of hetero-1,2,3,4,5-pentasubstituted ferrocenes

“…Since the discovery of ferrocene, 1,2 its derivatives have found applications in all areas of chemistry. [3][4][5] However, while monosubstituted, 1,1'-and 1,2-disubstituted ferrocenes account for a large number of reported applications, there is a need for highly substituted derivatives as the controlled introduction of various substituents allows their electronic [6][7][8][9] and steric 10,11 properties to be finely modulated. Albeit usual in metallocene chemistry, [12][13][14] pentamethylcyclopentadienyl (Cp*) and pentaphenylcyclopentadienyl ligands do not offer, with their five identical substituents, a high degree of properties' tuning.…”