Showing papers on "Ferrocene published in 2000"

Ferrocene and ferrocenyl derivatives in luminescent systems

Abstract: Owing to their fairly high stability under visible irradiation, ferrocene and ferrocenyl derivatives are widely used in luminescent systems. They are classical quenchers of excited states. Both energy and electron transfer may be involved, depending on the nature of the excited species. Inter- or intramolecular quenching are encountered. Applications span from the study of reaction mechanisms to that of organized or biological media. Recently, dyads and polyads designed for their ability to mimic photosynthetic centers or for their photodiode properties have also been obtained. Finally, the incorporation of a ferrocenyl derivative in a luminescent system does not necessarily lead to luminescence quenching. New applications are emerging, in which advantage is taken of the presence of ferrocene acting as a redox center: this gives optically and electrochemically active sensors. The present review encompasses the literature up to November 1999.

Long-Range Heterogeneous Electron Transfer Between Ferrocene and Gold Mediated By n-Alkane and N-Alkyl-Carboxamide Bridges

Abstract: Electron-transfer rates between ferrocene and gold were measured for two series of ferrocene-based alkanethiolate monolayers on gold electrodes. In one series, the bridge linking the ferrocene group to gold consisted of a simple alkane chain, and in the other, the bridge was modified such that the two methylene linkages immediately adjacent to the ferrocene group were replaced by a carboxamide linkage. Monolayers in both series were studied using a novel ac voltammetry method to measure the standard electron-transfer rate constants for oxidation/reduction of the ferrocene groups. Rate constants were nearly the same for pairs of molecules in the two series when the number of bonds in the direct pathway linking ferrocene to gold was the same, regardless of whether the group immediately adjacent to ferrocene was a pair of methylene units or a carboxamide unit. This observation suggests that the contribution of the carboxamide group to the overall bridge-mediated electronic coupling is not greatly different f...

An iron wheel on a tin drum: a novel assembly of a hexaferrocene unit on a tin-oxygen cluster

Abstract: Based on reactions known in organotin chemistry, the robust hexaferrocene assembly [{BuSn(O)OC(O)Fc} 6 ] is obtained in quantitative yield by the reaction of two commercially available reactants. The X-ray crystal structure shows a symmetric giant wheel arrangement of the ferrocene units attached in a cyclic manner to a central drumlike stannoxane core. Cyclic voltammetric studies show a single quasireversible oxidation peak.

HREELS and XPS Studies of Ferrocene on Ag(100)

Abstract: High-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS) have been used to investigate the adsorption of ferrocene on Ag(100) at 150 K. The HREELS data show that ferrocene adopts an orientation with the molecular axis perpendicular to the Ag(100) surface plane for low exposures. Additionally, no rehybridization is observed at the low temperature employed. Upon multilayer growth, however, the molecular axis becomes canted with respect to the surface normal. XPS for monolayer ferrocene gives Fe 2p binding energies of 707.9 and 720.8 eV for the 2p3/2 and 2p1/2 transitions, respectively, and C 1s binding energy of 284.9 eV. Monolayer surface coverage represents a molecular footprint of about one ferrocene per nine Ag surface atoms. Multilayer ferrocene grows in a layer-by-layer fashion and shows HREELS and XPS

Synthesis, Electrochemistry, and Interactions with β-Cyclodextrin of Dendrimers Containing a Single Ferrocene Subunit Located “Off-Center”

Abstract: Two series of dendrimers containing a single ferrocene unit located in the focal point of these macromolecules have been synthesized and characterized. The first series of dendrimers has considerable lipophilic character, with tert-butyl ester groups located in their peripheral regions. In contrast, the second series of dendrimers was obtained by the hydrolysis of these peripheral ester groups, yielding water-soluble dendrimers with carboxylic acid groups in their surfaces. The electrochemical properties of these macromolecules were strongly affected by the dendritic groups attached to the ferrocene subunits. Host−guest interactions between the water-soluble dendrimers and the well-known receptor β-cyclodextrin were also investigated. The dendritic groups were found to hamper markedly the formation of inclusion complexes between the cyclodextrin receptor and the dendrimer's ferrocene unit.

Synthesis of thiol-derivatized ferrocene-porphyrins for studies of multibit information storage

Abstract: One approach toward storage of multiple bits of information at the molecular level requires the construction of molecular architectures comprised of multiple redox-active units. Four new ferrocene−porphyrins have been synthesized to investigate questions concerning (1) the scope of redox-active molecules that can be employed in molecular information-storage schemes and (2) writing/reading rates as well as retention of charge in redox-active units located at different sites in a molecular architecture. Three of the ferrocene−porphyrins have linkers of different lengths between the ferrocene and porphyrin. The fourth ferrocene−porphyrin has two ferrocenes positioned at the lateral sites on the porphyrin. The latter architecture is designed to provide a shorter distance between the electroactive surface and the ferrocene while maintaining an upright orientation of the porphyrin. Each ferrocene−porphyrin affords three cationic oxidation states (ferrocene monocation, porphyrin monocation, porphyrin dication) i...

Flame inhibition by ferrocene and blends of inert and catalytic agents

Abstract: The production of the fire suppressant CF3Br has been banned, and finding a replacement with all of its desirable properties is proving difficult. Iron pentacarbonyl has been found to be up to several orders of magnitude more effective than CF3Br, but it is flammable and highly toxic. Ferrocene [Fe(C5H5)2], which is much less toxic and flammable than Fe(CO)5, can also be used to introduce iron into a flame. We present the first experimental data and numerical modeling for flame inhibition by ferrocene and find it to behave similarly to Fe(CO)5. A ferrocene mole fraction of 200 ppm reduced the burning velocity of slightly preheated premixed methane/air flames by a factor of two, and the effectiveness dropped off sharply at higher mole fractions. For air with a higher oxygen mole fraction, the burning velocity reduction was less. We also present experimental data and modeling for flames with ferrocene blended with CO2 or CF3H. The combination of the thermally acting agent CO2 with ferrocene mitigated the loss of effectiveness experienced by ferrocene alone at higher mole fractions. An agent consisting of 1.5% ferrocene in 98.5% CO2 performed as effectively as CF3Br in achieving a 50% reduction in burning velocity. Likewise, four times less CO2 was required to achieve the 50% reduction if 0.35% ferrocene was added to the CO2. In contrast, addition of 0.35% ferrocene to the hydrofluorocarbon CF3H reduced the CF3H required to achieve the 50% reduction in burning velocity by only about 25%. Thermodynamic equilibrium calculations predict that the formation of iron/fluoride compounds can reduce the concentrations of the iron-species oxide and hydroxide intermediates which are believed to be responsible for the catalytic radical recombination cycles.

Donor/Acceptor fulleropyrrolidine triads

Abstract: New C60-based triads, constituted by a fulleropyrrolidine moiety and two different electroactive units [donor 1-donor 2 (10, 15a,b), or donor 1-acceptor (17, 21)], have been synthesized by 1,3-dipolar cycloaddition reaction of azomethyne ylides to C60 and further acylation reaction on the pyrrolidine nitrogen. The electrochemical study reveals some electronic interaction between the redox-active chromophores. Triads bearing tetrathiafulvalene (TTF) and ferrocene (Fc) (10) or π-extended TTFs and Fc (15a,b) show reduction potentials for the C60 moiety which are cathodically shifted in comparison to the parent C60. In contrast, triads endowed with Fc and anthraquinone (AQ) (17) or Fc and tetracyanoanthraquinodimethane (TCAQ) (21) present reduction potentials for the C60 moiety similar to C60. Fluorescence experiments and time-resolved transient absorption spectroscopy reveal intramolecular electron transfer (ET) processes from the stronger electron donor (i.e., TTF or extended TTF) to the fullerene singlet e...

Optically and redox-active ferroceneacetylene polymers and oligomers

Abstract: The palladium-catalyzed Sonogashira reaction can be used to build optically active, oligomeric 1,2,3-substituted ferrocenes up to the tetramer, as well as polymers, by sequential coupling of optically active (ee > 98 %), planar chiral iodoferroceneacetylenes and ferroceneacetylenes. (SFC)-1-Iodoferrocene-2-carbaldehyde (1) was reduced to the alcohol and methylated to give the corresponding methyl ether, which was Sonogashira-coupled with HC(triple bond)CSiEt3, resulting in (RFc)-1-(C(triple bond)CSiEt3)-2-methoxymethylferrocene (4) (79%, three steps). Orthometalation with tBuLi followed by quenching with 1,2-diodoethane gave (RFc)-1-(C(triple bond)CSiEt3)-2-methoxymethyl-3-iodoferrocene (5). Deprotection of the acetylene with nBu4NF resulted in (RFc)-1-ethynyl-2-methoxymethyl-3-iodoferrocene (6), which was Sonogashira-coupled with itself to produce an optically active polymer. Deprotection of 4 with nBu4NF and Sonogashira coupling of the product with 5 resulted in the dinuclear ferrocene 9. Deprotection of 9 and coupling with 5, followed by deprotection of the resulting acetylene 11, gave the trinuclear ferrocene 12. Another such sequence involving 11 and 5 produced a tetranuclear ferrocene 13. To study the electronic communication in such oligomers in more detail, two symmetrical, closely interrelated, trinuclear ferrocenes 18 and 19 were synthesized. The redox potentials of all the ferrocenes and the ferroceneacetylene polymer were determined by cyclic and square-wave voltammetry. All the metallocenes were investigated by UV/Vis spectroscopy. A linear relationship was found between lambdamax and l/n (n=number of ferrocene units in the oligomer). The polymer displayed two redox waves in the cyclic voltammogram, at 0.65 and 0.795 V. The corresponding mixed-valence oligoferrocene cations were synthesized from four ferroceneacetylenes, and their metal-metal charge transfer bands were examined by UV/Vis-NIR. The resonance exchange integrals Had, calculated on the basis of spectral information from the metal - metal charge transfer (MMCT) bands, were between 290 and 552 cm-1.

π-Stacking between Pentafluorophenyl and Phenyl Groups as a Controlling Feature of Intra- and Intermolecular Crystal Structure Motifs in Substituted Ferrocenes. Observation of Unexpected Face-to-Face Stacking between Pentafluorophenyl Rings

Abstract: Ferrocenes containing phenyl and pentafluorophenyl substituents on the cyclopentadienyl rings have been prepared, and their solid-state structures were determined by single-crystal X-ray studies. In the homoleptic ferrocene Fe(Me 2 PhCp) 2 (5), no intra- or intermolecular face-to-face π-stacking of the aryl rings is observed, as expected. The intramolecular conformation has staggered cyclopentadienyl rings with the phenyl groups in an anti conformation. However, the mixed ferrocene Fe(Me 2 PhCp)(C 6 F 5 Cp) (6) crystallizes with eclipsed cyclopentadienyl rings and intramolecular π-stacking between the phenyl and pentafluorophenyl substituents. In addition the π-stacking between phenyl and pentafluorophenyl rings occurs between neighboring molecules, and controls the intermolecular crystal motif. Yet a different molecular architecture is observed in the homoleptic ferrocene Fe(C 6 F 5 Cp) 2 (2) which crystallizes surprisingly with intramolecularly π-stacked pentafluorophenyl rings. The overall crystal architecture in this case in controlled by π-stacking between pentafluorophenyl rings on one molecule with the cyclopentadienyl rings of neighbors, to afford a third structural motif. These results illustrate that both the intra and intermolecular solid-state structures of simple organometallic molecules can be controlled by stacking interactions involving pentafluorophenyl rings and suggest that these attractive interactions can be added to the repertoire of attractive forces used to effect crystal engineering in organometallic systems.

Alkali metal cation cooperative anion recognition by heteroditopic bis(calix[4]arene) rhenium(I) bipyridyl and ferrocene receptor molecules

Abstract: New heteroditopic bis(calix[4]arene) rhenium(I) bipyridyl (L1, L2) and ferrocene (L4) receptor molecules have been prepared and shown to bind a variety of anions at the upper rim and alkali metal cations at the lower rim. Proton NMR anion titration studies reveal the strength and selectivity of anion binding was dependent upon the presence of the calix[4]arene moieties and nature of the bridging group with the preorganised receptors L1 and L2 forming strong complexes in deuterated DMSO solutions. With L1, L2 and L4 co-bound lithium, sodium and potassium cations were found to significantly enhance the strength of iodide binding in acetonitrile solutions with the largest positive cooperative binding effect observed with L2 and sodium cations. Cyclic voltammetric investigations revealed L4 to electrochemically recognise carboxylate and halide anions. In the presence of lithium cations the electrochemical response of L4 to bromide anions was significantly amplified.

Intramolecular electronic interactions in conjugated ferrocene-π-extended-tetrathiafulvalene donor-π-donor molecular hybrids

Abstract: The synthesis of new hybrid ferrocene and π-extended tetrathiafulvalene (TTF) donor1-π-donor2 molecular assemblies 16a−c has been carried out by a Wittig−Horner reaction of the respective phosphonate esters 15a−c with 2-(2-ferrocenylvinyl)-9,10-anthraquinone (18) prepared by olefination of ferrocenecarboxaldehyde (14) and the anthraquinone phosphonium salt 17. Electrochemical studies show that the D1-π-D2 (D = donor) molecular assemblies 16a−c essentially retain the redox characteristics of both ferrocene and the π-extended TTF components and the effects of solvent, temperature, scan rate, and working electrode are significant. Most importantly, pronounced intramolecular electronic interactions between the two donor moieties were observed by cyclic voltammetry and Osteryoung square wave voltammetry in both the ground and charged states. Semiempirical calculations support the electrochemical observations.

Chiral Ferrocene Amines Derived from Amino Acids and Peptides: Synthesis, Solution and X-ray Crystal Structures and Electrochemical Investigations

Abstract: For the recognition of all but the simplest naturally occurring molecules, electrochemical sensors based on ferrocene will certainly require chiral centers. To advance the necessary chemistry, this work describes the synthesis and properties of ferrocene derivatives of enantiomerically pure amino acids, peptides, and other chiral amines. Ferrocene aldehyde is condensed with amino acid esters to yield the corresponding Schiff bases 2, which are reduced by NaBH4 in methanol to the ferrocene methyl amino acids 3. An X-ray single-crystal analysis was carried out on the phenylalanine derivative 3a (monoclinic space group P21, a = 10.301(1) A, b = 9.647(1) A, c = 18.479(2) A, β = 102.98(2)°, Z = 4). Further peptide chemistry at the C terminus proceeds smoothly as demonstrated by the synthesis of the ferrocene labeled dipeptide Fc-CH2-Phe-Gly-OCH3 5 (Fc = ferrocenyl ((η-C5H4)Fe(η-C5H5))). We also report the synthesis of the C,N-bis-ferrocene labeled tripeptide Phe-Ala-Leu and its electrochemical characterization...

Effect of Interchain Hydrogen Bonding on Electron Transfer through Alkanethiol Monolayers Containing Amide Bonds

Abstract: Two-component self-assembled monolayers (SAMs) were designed as model systems for the studies of the factors controlling long-range electron-transfer processes. The monolayers, which were attached to a gold electrode, consisted of two components: an alkanethiol with an amide moiety in the chain and an electroactive terminal ferrocene group and a nonelectroactive thiol acting as the diluent of the electroactive centers. The diluent was either a simple alkanethiol or an alkanethiol containing an amide group. The rates of electron transfer for the electroactive ferrocene group were calculated using the data obtained by voltammetry and chronoamperometry. Upon substitution of the diluent alkanethiol for an alkanethiol containing an amide group, the rate constant of the oxidation of ferrocene headgroups increased more than 3 times, while the reorganization energy remained unchanged. The increased electronic coupling between ferrocene and the electrode was ascribed as due to the contribution of the hydrogen bon...

Functionalised oligoenes with unusual topologies: Synthesis, electrochemistry and structural studies on redox-active [3]- and [4]-dendralenes

Abstract: New [3]- and [4]-dendralenes bearing electron-donor 1,3-dithiole and ferrocene substituents have been synthesised. Compounds 8, 15 and 17 have been characterised by single-crystal X-ray diffraction. Two of the dithiole rings of 8 are conjugated (dihedral angle 9 degrees), while the third dithiole ring is almost orthogonal to this plane, and hence its pi-electron system is isolated. For the dendralene precursor molecule 15, the substituted cyclopentadienyl ring, two C=C bonds and fused dithiole and dithiine rings comprise an extended pi-conjugated system. In molecule 17 the potential conjugation path C(6)C(3) C(4)C(5)-C5H5 is distorted by an 8 degrees twist around the C(3)-C(4) bond and a 7 degrees twist around the C(5)-C(21) bond, and the delocalisation along the chain is insignificant. Solution electrochemical data demonstrate that the dendralenes are strong pi-electron donors, which give rise to dication, radical trication or tetracation species. Spectroelectrochemical studies on compounds 7 and 10 suggest that the radical species are situated within the linear 1,2-ethylenediylidene moieties and that a conformational change may occur at the dication redox stage. UV/Vis spectroscopic data are consistent with poor cross-conjugation in these systems.