Redox-active crown ethers: transmission of cation binding to a redox centre via a conjugated link

Abstract

The binding of Li+ to aza-15-crown-5-linked ferrocenes results in a shift of the ferrocene oxidation wave to more positive potentials when a conjugated link exists between the azacrown nitrogen atom and the redox centre.Interest in switchable metal ion binding and transport has resulted in a number of recent papers concerning redox-active ionophores. In general these compounds have been designed so that conformations may be adopted in which the guest metal ion is held close to the redox centre.1-7 In this paper we seek to examine electrochemical recognition of metal ion binding via a conjugated link between ionophore and redox centre as an alternative to 'through-space' interactions. We report here the synthesis of the first examples, (1) and (2), of a class of compound in which ferrocene is linked through a conjugated system to the remote nitrogen atom of the aza-15-crown-5 unit ,8 and present evidence that metal-ion binding perturbs the redox potential of the ferrocene/ferricinium couple by a mechanism involving transmission of the electrostatic effect through the n-electron system.Compound (1) and the acyclic analogue (3)t were obtained by reaction of the phosphonium salt (4)9 with N-(bformylphenyl)aza-15-crown-510 or 4-dimethylaminobenzaldehyde, followed by separation of cisand trans-isomers (Scheme 1). Hydrogenation of (1) afforded compound (5). The meth-

The First X‐ray Characterized Monosubstituted Ferrocenyl Azacrown Chalcone: Focus on Its Calcium Interaction/Electrochemical Detection Studies

“…The first irreversible oxidation process of compound 2 , whose E 1/2 value is 0.92 V, may be attributed to the oxidation potential of the organic amine moiety ( E 1/2 Org) 8. Moreover, it lies in the range of values reported for the oxidation of some azaferrocenyl compounds 16. Interesting studies on the oxidation of organic and ferrocenyl aromatic and aliphatic amines17–20 and our previous results1d,8 suggest that different and/or competitive mechanisms (e.g.…”

“…Upon comparing the reported data concerning theelectrochemical detection of lithium by [(C 5 H 5 )Fe(C 5 H 4 CH=CHC 6 H 4 NMe 2 )]16 and by [Fe(C 5 H 4 CONR 2 ) 2 ]22with the changes observed by cyclic voltammetry for compound 2 upon calcium addition, it appears that the Ca 2+ complexation process could involve the whole organic part of molecule 2 since both its oxidation and reduction processes are entirely perturbed. Therefore, to determine in particular whether the azacrown moiety and/or the CO function were involved in this complexation (or interaction) process, a thorough NMR study was undertaken.…”

Ca2+ vs. Ba2+ electrochemical detection by two disubstituted ferrocenyl chalcone chemosensors. Study of the ligand–metal interactions in CH3CN

“…The variations induced by the presence of the Ba 2+ cation are not common: the oxidation potential of Fe II /Fe III couple remains roughly the same, while the first oxidation potential of the organic part increases. For classical electrochemical ferrocenyl cation sensors, the intensity of the wave corresponding to the latter oxidation potential generally decreases upon salt addition, or this wave disappears [23]. Most of the time, this oxidation process is also situated after that of the ferrocene unit.…”

Electrochemical behaviour of tetraazamacrocyclic nickel(II) complexes functionalized with crown ethers

“…Only a few papers considering the electrooxidation of aromatic crown ethers are available in literature. Two of them concern N-phenyl-aza-15-crown-5 ether [12,13]. Cyclic voltammogram of this ether showed single, one-electron wave connected with creation of radical cations, which underwent coupling reaction to form a dimmer.…”