Ferrocenium Cations Research Articles

A Kinetic Study of the Electron-Transfer Reaction of the Phthalimide-N-oxyl Radical (PINO) with Ferrocenes

A kinetic study of the one-electron oxidation of a series of ferrocenes (FcX: X = H, CO2Et, CONH2, CH2CN, CH2OH, Et, and Me2) by PINO generated in CH3CN by reaction of N-hydroxyphthalimide (NHPI) with the cumyloxyl radical produced by 355 nm laser flash photolysis of dicumyl peroxide has been carried out. Ferrocenium cations were formed, and the reaction rate was determined by following the decay of PINO radical at 380 nm as a function of the FcX concentration. Rate constants were very sensitive to the oxidation potential of the substrates and exhibited a good fit with the Marcus equation, from which a lambda value of 38.3 kcal mol(-1) was calculated for the reorganization energy required in the PINO/ferrocenes electron-transfer process. Knowing the ferrocene/ferrocenium self-exchange reorganization energy it was possible to calculate a value of 49.1 kcal mol(-1) for the PINO/PINO- self-exchange reaction in CH3CN. Moreover, from the Marcus cross relation and the self-exchange rates of ferrocene and dimethylferrocene, the intrinsic reactivity of PINO in electron-transfer reactions has been calculated as 7.6 x 10(2) M(-1) s(-1). The implications of these values and the comparison with the electron-transfer self-exchange reorganization energies of peroxyl radicals are briefly discussed.

Magnetic behavior of polyaniline doped with oxidized ferrocenesulfonic acid

Ferrocenesulfonic acid (FSA) was oxidized by iodine (I 2) and then used as dopant for polyaniline emeraldine base. The resulted polyaniline showed an electrical conductivity of 4.50 × 10 −2 S/cm and a ferromagnetic interaction with a positive Weiss constant of 15 K, the magnetic behavior is attributed to the ferromagnetic coupling between ferrocenium cations in the counter-ions along the polyaniline chain.

Hexagonal Supramolecular Architectures from Ferrocenium Cations Incorporating [Ni(mnt)2]− Columns: Structures and Properties of [Alkylferrocene][Ni(mnt)2]− Charge‐Transfer Complexes (mnt=maleonitriledithiolate)

The crystal architecture, magnetic properties, and thermodynamic properties of [n-butylferrocene][Ni(mnt)2] (1), [tert-butylferrocene][Ni(mnt)2] (2), [1,1'-diethylferrocene][Ni(mnt)2] (3), and [1,1'-diisopropylferrocene][Ni(mnt)2] (4) were investigated (mnt=maleonitriledithiolate). These complexes exhibit a unique supramolecular structure in which the ferrocenium cations constitute honeycomb-like assembled structures surrounding columns of the anions. For 1, the cations form a dimer through a very short intermolecular ferrocene-ferrocene distance of 3.28 A, which mediates an antiferromagnetic interaction with a singlet-triplet energy gap of 5 K. First-order phase transitions occur in 1-3 at 364, 361, and 350 K, respectively, accompanied by thermal hysteresis.

Tetraurea calix[4]arenes with sulfur functions: synthesis, dimerization to capsules, and self-assembly on gold

Various calix[4]arene derivatives, fixed in the cone conformation by decylether groups and functionalized at their wide rim by urea residues, were synthesized. In two compounds (,) sulfur functions were attached to the urea groups via different spacers in order to allow binding to metal surfaces. While they exist as single molecules in polar solvents, tetraurea calix[4]arenes of this type () combine to form dimeric capsules in aprotic, apolar solvents. A solvent molecule is usually included in such a capsule, if no guest with a higher affinity is present. In the presence of an equimolar amount of the tetratosylurea, the exclusive formation of heterodimers, consisting of one molecule of and, is observed. The homo- and heterodimerization of the newly prepared derivatives, were studied by 1H NMR to establish the conditions under which they exhibit the desired dimerization behaviour. Self-assembled monolayers (SAMs) were formed using the single calix[4]arenes, and the heterodimeric capsules. Chloroform, dichloromethane and ferrocenium cations were used as guests in these immobilized heterodimeric capsules. The particular supramolecular architecture of the heterodimers should ensure that, after the immobilization on the metal surface, decomposition of the capsules and release or exchange of the guest is impossible or at least hindered. The self-assembly process and the stability of SAMs formed by capsules filled with ferrocenium cations in electrolyte solutions were tested with surface plasmon spectroscopy. The inclusion of guests, such as dichloromethane or ferrocenium, in the immobilized capsules were confirmed by classical surface plasmon spectroscopy, by gold nanoparticle absorption spectroscopy and by time-of flight secondary ion mass spectrometry (ToF-SIMS). The film stability and quality was tested by cyclic voltammetry.

Design of reversible multi-electron redox systems using benzochalcogenophenes containing aryl and/or ferrocenyl fragments

2,3-Disubstituted benzo[ b]thiophenes, 1,3-disubstituted benzo[ c]thiophenes, and 1,3-disubstituted benzo[ c]selenophene have been systematically and selectively synthesized from benzo[ b]thiophene or phthaloyl dichloride as a starting material, respectively. Characterization of the molecules was performed by physical and spectroscopic means and X-ray crystallographic analyses. The cyclic voltammograms of the chalcogenophene derivatives containing aryl fragments showed well-defined reversible both anodic and cathodic steps derived from the unusually stable 5π chalcogenophene radical cations and 7π chalcogenophene radical anions. The cyclic voltammograms of the novel chalcogenophene derivatives containing ferrocenyl fragments showed a well-defined reversible cathodic step derived from the unusually stable 7π chalcogenophene radical anions and two distinct reversible anodic steps derived from ferrocenium cations separated from each other by a thiophene-heterocycle. The radical character of several novel 7π chalcogenophene radical anions was measured by ESR spectroscopy.

Synthesis, structure, and both cathodic and anodic reversible redox reactions of benzochalcogenophenes containing ferrocene units

2,3-Diferrocenylbenzo[ b]thiophene and 1,3-diferrocenylbenzo[ c]thiophene have been systematically and selectively synthesized from benzo[ b]thiophene and phthaloyl dichloride, respectively. Characterization of the molecules was performed by physical and spectroscopic means and X-ray crystallographic analyses. The cyclic voltammograms of the novel thiophene derivatives containing ferrocene fragments showed a well-defined reversible cathodic step derived from the unusually stable thiophene radical anions and two distinct reversible anodic steps derived from ferrocenium cations separated from each other by a thiophene heterocycle. 1,3-Diferrocenylbenzo[ c]selenophene was also synthesized in a similar manner for formation of 1,3-diferrocenylbenzo[ c]thiophene by the use of bis(dimethylaluminum) selenide as a selenating reagent.

Reactivity of ferrocenium cations with molecular oxygen in polar organic solvents: Decomposition, redox reactions and stabilization

The behaviour of chemically or electrochemically generated ferrocenium cations has been studied in some polar organic solvents (DMF, DMSO, acetonitrile, acetone, methylene chloride) under molecular oxygen. Adducts between oxygen and ferrocenium species can differently evolve according to the solvent (oxidizable or not) and the absence or the presence of another reagent. A rapid decomposition of ferrocenium cations is observed in the absence of another substrate. In the presence of some substrates and antioxidants, the stability of ferrocenium cations towards molecular oxygen notably increases and in some cases redox reactions take place with formation of ferrocene.

The (Calix[4]arene)chloromolybdate(IV) Anion [MoCl(Calix)]-: A Convenient Entry into Molybdenum Calix[4]arene Chemistry

The complex (HNEt(3))[MoCl(NCMe)(Calix)] (1), prepared from the reaction of [MoCl(4)(NCMe)(2)] with p-tert-butylcalix[4]arene, H(4)Calix, in the presence of triethylamine, has been used as a source of the d(2)-[Mo(NCMe)(Calix)] fragment. Complex 1 is readily oxidized with PhICl(2) to afford the molybdenum(VI) dichloro complex [MoCl(2)(Calix)] (2). Both complexes are a convenient entry point into molybdenum(VI) and molybdenum(IV) calixarene chemistry. The reaction of 1 with trimethylphosphine and pyridine in the presence of catalytic amounts [Ag(OTf)] led to the formation of neutral d(2) complexes [Mo(PMe(3))(NCMe)(Calix)] (3) and [Mo(NC(5)H(5))(NCMe)(Calix)] (4). The role of the silver salt in the reaction mixture is presumably the oxidation of the chloromolybdate anion of 1 to give a reactive molybdenum(V) species. The same reactions can also be initiated with ferrocenium cations such as [Cp(2)Fe](BF(4)). Without the presence of coordinating ligands, the dimeric complex [[Mo(NCMe)(Calix)](2)] (5) was isolated. The reaction of 1 with Ph(2)CN(2) led to the formation of a metallahydrazone complex [Mo(N(2)CPh(2))(NCMe)(Calix)] (6), in which the diphenyldiazomethane has been formally reduced by two electrons. Molybdenum(VI) complexes were also obtained from reaction of 1 with azobenzene and sodium azide in the presence of catalytic amounts of silver salt. The reaction with azobenzene led under cleavage of the nitrogen nitrogen bond to an imido complex [Mo(NPh)(NCMe)(Calix)] (7), whereas the reaction with sodium azide afforded the mononuclear molybdenum(VI) nitrido complex (HNEt(3))[MoN(Calix)] (8).

Magnetic studies on hexahalorhenate(IV) salts of ferrocenium cations [Fe(C5R5)2]2[ReX6] (R = H, CH3; X = Cl, Br, I).

The hexahalorhenate(IV) salts of formula [Fe(C5H5)2]2[ReX6], with X = Cl (1), Br (2), and I (3), and [Fe(C5Me5)2]2[ReX6], with X = Cl (4), Br (5), and I (6) ([Fe(C5Me5)2]+ = decamethylferrocenium cation), have been synthesized and the structures of 1, 2, and 4 determined by single-crystal X-ray diffraction. 1, 2, and 4 crystallize in the orthorhombic system, space groups Pbca (1 and 2) and Ibam (4), with a = 14.099(2) A, b = 16.125(2) A, and c = 22.133(15) A, for 1, a = 14.317(3) A, b = 16.848(3) A, and c = 22.099(2) A for 2, and a = 15.8583(5) A, b = 15.9368(5) A, and c = 16.9816(6) A for 4. The three structures are made up of discrete [ReX6]2- anions and ferrocenium cations held together by electrostatic forces. There are anion-anion contacts in 1 and 2 but only through one direction. The [ReX6]2- octahedra are arranged along the y axis forming chains of Re and X atoms, -Re-X...X-Re-X...X-Re-, where the intermolecular X...X distances are shorter than the van der Waals distances. A somewhat greater separation between the anions occurs in 4. The magnetic properties of 1-6 were investigated in the temperature range 2.0-300 K. 1, 2, 4, and 5 exhibit an antiferromagnetic coupling between the anions, whereas a ferromagnetic coupling between anions and cations is the dominant interaction in 3. 6 behaves as a magnetically isolated compound, its susceptibility being the simple addition of the independent contributions of the uncoupled paramagnetic cations and anions.

Electrochemically assisted injection – a new approach for hyphenation of electrochemistry with capillary-based separation systems

A new concept based on the electrochemical conversion of analyte species during the injection into capillary flow systems is presented. This approach is termed electrochemically assisted injection (EAI). In a specially designed injection cell containing the analyte solution a conversion efficiency of about 83% can be achieved. Potassium octacyanotungstate(IV) served as a model compound for the analytical characterisation of EAI applying capillary flow injection analysis with double-pulse amperometric detection. Capillary electrophoresis experiments were performed using EAI to study the electrochemical oxidation of various ferrocene derivatives in acetonitrile solution. The electropherograms recorded with UV detection show separated signals for the ferrocene compounds and their oxidation products. The migration behaviour and the stability of ferrocenium cations and other reaction products were investigated.

Redox properties of anion-exchangeable polypyrrole substituted by (ferrocenylmethyl)ammonium groups and their binding interaction with solution-dissolved calix[6]arene- p-hexasulfonate

This report describes charge transport in a (ferrocenylmethyl)ammonium group-substituted anion-exchangeable polypyrrole and discusses the binding interaction of the ferrocenyl group with solution-dissolved calix[6]arene- p-hexasulfonate. The impedance response of 0.8–1.1 μm thick film modified electrodes corresponded with the behavior expected from the diffusional charge-transport model for thin films. Since the charge-compensating counterions diffused rapidly in the polyelectrolyte film, the rate of intermolecular electron hopping limited that of charge transport. The polycationic film effectively extracted the calixarene from its dilute aqueous solutions. It shifted the half-wave potential of the ferrocenyl group to less positive values, indicating the greater binding affinity of the anionic host for ferrocenium cations than for uncharged ferrocenes. The inclusion complexation decreased the concentrations of the free redox couple; thus the host of 1-mM concentration increased the interfacial charge-transfer resistance by a factor of 70. Since the rates of the coupled chemical reactions were fast, they influenced the electrode kinetics insignificantly.

Water stability and cytotoxic activity relationship of a series of ferrocenium derivatives. ESR insights on the radical production during the degradation process.

The cytotoxicity of some ferrocenium salts and the lack of activity of the corresponding ferrocenes has been already demonstrated. The cytotoxic activity in different conditions of decamethylferrocenium tetrafluoroborate (DEMFc(+)) in comparison with four other ferrocenium derivatives on MCF-7 cell line is reported. The relative stability in aqueous solutions with different buffering agents is investigated by means of UV-vis spectroscopy and correlated to the cytotoxic properties of the compounds. DEMFc(+), the most stable compound, shows the highest efficiency in inhibiting cell growth (IC(50) 35 microM, for 48 h treatment). Relaxation time measurements point out the involvement of water molecules in the degradation process. ESR results confirm the ability of ferrocenium cations to produce oxygen radical species as a consequence of their degradation in water. Oxygen-dependent formation of both hydroxyl and superoxide radicals is established by the spin-trapping technique. A direct evidence of the DEMFc(+) radical production into the viable cells is obtained by means of fluorescence-activated cell sorter (FACS) analysis that reveals a dose-dependent growth of 8-oxoguanine, the initial product of the guanine oxidation. This DNA oxidative stress justifies the cytotoxic effect of DEMFc(+). Furthermore, the cytotoxic cooperative effect of bleomycin, an iron-dependent antitumor drug, and DEMFc(+) has been tested. We have demonstrated the synergic effect between the two drugs, that is explained by the complementary oxidative damage inflicted to DNA as well as by the increasing of bleomycin activation by the iron(II/III) species available in the cell compartment from ferrocenium degradation.

Electrooxidation of substituted ferrocenes: indirect oxidation of the side chain

Anodic oxidation of ferrocenes bearing an electron-withdrawing substituent with a H-atom in the α-position (ferrocenylacetic acid 1a, ferrocenylacetonitrile 2a) has been investigated by cyclic voltammetry and by macroscale electrolysis in a flow cell fitted with a porous graphite felt anode. Oxidation of ferrocenes ( 1a, 2a) into their ferrocenium cations ( 1a +, 2a +) increases the acidity of the H-atom in the α-position to the cyclopentadienyl ligand. The deprotonation is favoured by a basic medium to give a radical ( 1b, 2b). According to the substrate, the radical can be oxidised ( 1b) or can dimerise ( 2b). Exhaustive electrolysis of 1a leads to ferrocenecarboxaldehyde after multi-step reactions (redox reactions and nucleophilic attack by H 2O). Electrolysis of 2a affords a dimer which was further oxidised into 1,2-diferrocenyl-1,2-dicyano ethylene.

Preparation and characterization of various N-substituted-2-aza-[3]-ferrocenophanes and their chemical and electrochemical properties

RuCl 2(PPh 3) 3 catalyzed condensation of 1,1′-ferrocenedimethanol with primary amines afforded N-alkyl- or N-aryl-2-aza-[3]-ferrocenophanes which were characterized by 1H and 13C NMR spectra. X-ray crystallography of N-(4-butylphenyl)-2-aza-[3]-ferrocenophane unequivocally revealed its mononuclear structure. The N–C (aryl) bond distance is shorter than the N–CH 2 single bond due to extension of π-conjugation of the aromatic ring to the nitrogen atom. N-Hexyl-2-aza-[3]-ferrocenophane reacts with methyl iodide to give the N-methylated product which was characterized by NMR spectroscopy and X-ray crystallography. N-Aryl-2-aza-[3]-ferrocenophanes exhibited reversible redox between ferrocene and ferrocenium cations and an irreversible oxidation peak at a higher oxidation potential.

X-ray Crystal Structures and the Facile Oxidative (Au−C) Cleavage of the Dimethylaurate(I) and Tetramethylaurate(III) Homologues

Dimethylaurate(I) has been prepared as the crystalline tetrabutylammonium salt for comparison with the known tetramethylaurate(III) analogue. The linear structure of dimethylaurate(I) and the square-planar structure of tetramethylaurate(III) have both been confirmed by X-ray crystallography. One-electron oxidation of dimethylaurate(I) by either ferrocenium or arenediazonium cations produces the metastable dimethylgold(II) intermediate, which can be trapped as the paramagnetic 9,10-phenanthrenequinone (PQ) adduct. Otherwise, dimethylgold(II) is subject to rapid reductive elimination of ethane and affords metallic gold (mirror). The analogous oxidation of tetramethylaurate(III) by ferrocenium, arenediazonium, or nitrosonium cations also proceeds via electron transfer to generate the putative tetramethylgold(IV) intermediate. The highly unstable (CH3)4AuIV spontaneously undergoes homolytic cleavage to produce methyl radical and the coordinately unsaturated trimethylgold(III), which can be intercepted by adde...

Regulatory role of surfactants in the kinetics of glucose oxidase-catalyzed oxidation ofd-glucose by ferrocenium andn-butylferrocenium ions

The effect of micelles of different surfactants (cationic, anionic, and neutral) on the kinetics of the glucose oxidase-catalyzed reduction of ferrocenium cations RFc+ (R=H, Bun) byd-glucose was studied by spectrophotometry. In micellar media of Triton X-100 and sodium dodecyl sulfate (SDS), the Michaelis dependence of the reaction rate on the HFc+ concentration is observed, while this dependence has an extreme character in cationic micelles of cetyltrimethylammonium bromide (CTAB). The nature and concentration of surfactants of all types have a slight effect on the rate of reduction of HFc+. The level of enzymatic activity is approximately equal in the case of Triton X-100 and CTAB and is considerably lower in the SDS micelles. On going from HFc+ to BunFc+, the reaction rate is maximum in the cationic CTAB micelles, the anionic SDS micelles exhibit almost no activity, and the activity has an intermediate value in neutral micelles of Triton X-100. The conditions are presented under which the micellar medium controls the catalytic activity of glucose oxidase with respect to ferrocenium cations.

Active Control of Interfacial Properties: A Comparison of Dimeric and Monomeric Ferrocenyl Surfactants at the Surface of Aqueous Solutions

The surface activity and micellization of the dimeric, ferrocenyl surfactant Fc(CH2)8N+(CH3)2(CH2)3(CH3)2N+(CH2)8Fc 2Br- (DI2+), where Fc = ferrocene = [η5-C5H5]Fe[η5-C5H5], are compared and contrasted to those of the monomeric, ferrocenyl surfactant Fc(CH2)8N+(CH3)3Br- (I+) in aqueous solution. Dimeric DI2+, when compared to I+, was measured to be surface active in aqueous solutions of 0.1 M Li2SO4 at lower concentrations (0.001 mM of DI2+ versus 0.03 mM of I+) and found to possess a lower critical micelle concentration (cmc) (0.02 mM for DI2+ as compared to 2.0 mM for I+). Linear sweep cyclic voltammograms show that the (two) ferrocenes of DI2+ oxidize independently to form ferrocenium cations. Light-scattering measurements confirm that DI2+ forms micelles in solution and that oxidation of DI2+ to DI4+ is accompanied by the disassembly of micelles. Reduction of DI4+ back to DI2+ reforms the micelles. Measurements of surface tension demonstrate that oxidation of DI2+ to DI4+ leads to desorption of surfactant from the surface of aqueous solutions. Because DI4+ was not measurably surface active at concentrations less than 0.4 mM, oxidation of DI2+ to DI4+ made possible changes in surface tension of 21 mN/m over a range of concentrations that exceeded an order of magnitude (0.02−0.4 mM). Control of the oxidation state of I+, in contrast, permits changes in surface tension of 20 mN/m at one concentration (2.0 mM) only. Dimeric redox-active surfactants in combination with electrochemical methods do, therefore, permit active control of interfacial properties of aqueous solutions over a wider range of surfactant concentrations than is possible with the corresponding monomeric redox-active surfactant. Simple models for the standard free energies of micellization and adsorption can describe the lower cmc of DI2+ as compared to I+ and the wider range of concentrations over which oxidation of DI2+ leads to changes in surface tension as compared to I+.

Anodic co-oxidation of urazole and ferrocenes: first trapping of cyclopentadienols

Cyclopentadien-5-ols, the major products resulting from decomposition of some ferrocenium cations by molecular oxygen, are regio- and stereo-selectively trapped by 4-phenyl-1,2,4-triazoline-3,5-dione.

The effects of an interannular bridge on the electronic structure of ferrocenium cations

Minor perturbations caused by the interannular trimethylene bridges in a series of ferrocenium cations have pronounced effects on the electronic structure. The X-ray structure of 1,1′:3,3′-bis(propane-1,3-diyl)ferrocenium triiodide has been determined at 298 K: monoclinic, C2/c, a = 11.110(2) A ̊ , b = 9.372(2) A ̊ , c = 18.003(2) A ̊ , β = 107.294(9)°, Z = 4, D calc = 2.401 g cm −1, R F = 0.033, and R WF = 0.040. Compound 1,1′:2,2′-bis(propane-1,3-diyl)ferrocenium triiodide crystallizes in orthorhombic space group Pnma with four molecules in a unit cell with dimensions a = 8.699(1) A ̊ , b = 13.461(2) A ̊ , c = 15.747(3) A ̊ ; R F = 0.041, R WF = 0.042. The compound 1,1′:2,2′:4,4′-tri(propane-1,3-diyl)ferrocenium triiodide crystallizes in orthorhombic space group Cmca with sixteen molecules in a unit cell with dimensions a = 18.456(4) A ̊ , b = 33.401(7) A ̊ , and c = 13.470(5) A ̊ . The final discrepancy factors are R F = 0.077, and R WF = 0.090. An unusually large quadrupole splitting ( ΔE Q = 0.936 mm s −1) is seen in the Mössbauer spectrum of 1,1′:2,2′-bis(propane-1,3-diyl)ferrocenium triiodide at 300 K. We suggest that the larger ΔE Q value is mainly a result of the metal non-bonding orbitals (d x 2− y 2 , d xy ) starting to interact with the ligand π orbitals as the Cp rings are bent back. The magnetic susceptibility measurements indicate that the electronic ground state for the interannular trimethylene bridge ferrocenium cations is 2 E 2g. The visible absorption spectra of the various ferrocenium cations show a low-energy ligand-to-metal 2 E 2g→ 2 E 1u charge-transfer transition. In the case of 1,1′:2,2′:4,4′-tri(propane-1,3-diyl)ferrocenium triiodide, a vibrational structure was observed for this charge-transfer transition at room temperature.

Pronounced effect of interannular trimethylene bridges on the rate of intramolecular electron-transfer in mixed-valence biferrocenium salts. A novel electronic ground state of ferrocenium cations

X-ray structure determinations of two new constitutional isomers of biferrocene, the effects of interannular trimethylene bridges on intramolecular electron-transfer rates in the solid state, and characterization of the electronic ground state of a series of ferrocenium cations are reported.