Redox-active Ferrocenyl Research Articles

Dynamic behavior and alkyne insertion reactions of alkenyl- and thiolate-bridged diiron carbonyl complexes

The alkenyl- and thiolate-bridged diiron carbonyl complexes [Fe2(μ-SC6H4CR1CH)(CO)6] (R1 = H or Me), which are derived from [Fe3(CO)12] and benzothiophenes, reacted with alkynes (R2CCR3) under photoirradiation conditions to form the acyl complexes [Fe2{μ-SC6H4CR1CHCR2C(R3)CO}(CO)5]. In this reaction, an alkyne and CO are inserted into the Fe–alkenyl bond, and the bulky substituents of alkynes, including a redox active ferrocenyl group, occupy the R3 position. To elucidate the reaction pathway, the reaction of the in situ generated acetonitrile complex [Fe2(μ-SC6H4CHCH)(CO)5(NCCH3)] with ethynylbenzene was monitored by 1H NMR spectroscopy. The results demonstrated that the acetonitrile complex undergoes facile insertion of the alkyne, which is followed by CO insertion to give the corresponding acyl complex [Fe2{μ-SC6H4(CH)3C(Ph)CO}(CO)5]. The reactivity of the bridging alkenyl moiety is related to the dynamic behavior of the alkenyl-thiolate ligand (SC6H4CHCH)2- as well as the entering alkyne. Temperature dependent 31P NMR measurements of the dmpm-bridged complex [Fe2(μ-SC6H4CHCH)(μ-dmpm)(CO)4] (dmpm = bis(dimethylphosphino)methane) revealed that the activation parameters for the flip-flop motion of the alkenyl-thiolate ligand are ΔH‡ = 46.7(7) kJ mol-1 and ΔS‡ = −46(2) J mol-1 K-1.

Ternary nanocomposite of GQDs-polyFc/Fe3O4/PANI: Design, synthesis, and applied for electrochemical energy storage

Redox-active and conductive polymers and transition metal oxides are appearing group of faradaic battery-type electrode materials that exhibit improved electrochemical properties in supercapacitors. Herein, we report a new class of ferrocenyl-based nanocomposite electrodes for the development of high-performance supercapacitors using a simple physical mixing method of redox active ferrocenyl modified GQDs with conductive polymer including PANI and Fe3O4. Having the popular redox-active organometallic compound like (Fc), PANI, and Fe3O4 as integrated constituent components, the obtained electrode materials exhibit remarkably charge storage and delivery capabilities. The structural properties of the electrode materials investigate by appropriate analyses. The highest capacity, energy density, and power density are to be 295 mAh g−1, 62.1 Wh kg−1 and 4140 W kg−1 for the nanocomposite, respectively. These results which can be attributed to the synergistic behavior of the different types of electrode materials in the hybrid nanocomposites, leading to the improved electrochemical performance. In addition, the cycling performance is tested with 5000 long cycles. The retention of charge storage (91.45%) after 5000 cycles at a current density of 1 A g−1 shows the great potential of GQDs-PolyFc/Fe3O4/PANI nanocomposites as electrode materials for future energy storage technologies. Finally, we conclude with some suggestions for future work.

Introducing a redox-active ferrocenyl moiety onto a polythiophene derivative towards high-performance flexible all-solid-state symmetric supercapacitors

By introducing a ferrocenyl moiety on the backbone of a polythiophene derivative, enhanced performances of flexible all-solid-state symmetric supercapacitors fabricated with such a conductive metallopolymer were achieved.

Isomeric triarylamine-ferrocene mixed-valence systems: Syntheses, structural-(spectro)electrochemical analysis, and theoretical calculations

Six novel triarylamine (TAA)–ferrocenyl conjugates (1–6) were prepared and characterized using molecular spectroscopic and crystallographic methods. Different species with a corresponding valences of 1n+−6n+ (n = 0, 1) were investigated using cyclic voltammetry, UV–Vis–NIR spectroelectrochemistry, and quantum–chemical calculations. Electrochemical analysis of two groups of isomeric complexes (1–2) and complexes (3–6) revealed that the effective distance between redox–active ferrocenyl and TAA remarkably influenced the redox potential difference (ΔE). NIR peaked at 1142 and 1153 nm from singly oxidized complexes 1+ and 3+, thereby indicating that 1+ and 3+ were stable in CH2Cl2 solution and featured obvious IVCT characters. These findings were proved as NAr3 → Fc charge transfer by TDDFT predictions. Calculations of spin density distribution showed that the monocations 1+−6+ all exhibited remarkably identical charge distributions with dominant metal (Fc)-localized characteristics.

A Gold Quartet Framework with Reversible Anisotropic Structural Transformation Accompanied by Luminescence Response

Summary Hierarchy and chirality are the fundamental characteristics of biomolecules. Chemistry on hierarchical self-assembly and spontaneous symmetry breaking helps to uncover the mechanism of living activities and the origin of chirality in nature. Herein, we describe a chiral gold quartet framework (GQF) with C4-symmetric structure hierarchically aggregated from an achiral anionic [Au10(dpptrz)4S4]2− (dpptrz-Au10), which was acquired via click-reaction-induced and Au(I)⋅⋅⋅Au(I)-interaction-directed cluster-to-cluster transformation (CCT) from the rationally designed [(dppa)6Au18S8]2+ (dppa-Au18). Inter-cluster hydrogen bonding and alkali ion coordination were observed to assist the hierarchical self-assembly and chiral self-organization of the GQF. Upon exposing the crystal to vacuum, the bottom-up constructed GQF showed an anisotropic structural transformation accompanied by a visual luminescence change in a single-crystal-to-single-crystal (SCSC) manner that became reversible upon removal of vacuum. This research largely advances the potential of polynuclear gold(I)-sulfido clusters in hierarchical self-assembly and luminescent materials.

Synthesis and viscoelastic properties of gemini surfactants containing redox-active ferrocenyl groups

A type of electro-responsive threadlike micelle (TLM) was formed using new cationic gemini surfactants Fc11-n-11Fc with redox-active ferrocenyl groups in the gemini alkyl chains. By varying the alkyl spacer length, we synthesized several kinds of Fc11-n-11Fc-based gemini surfactants with n = 3, 4, 6, and characterized their viscoelastic behavior, surface activity, and redox properties in aqueous solutions through the use of oscillatory rheology, surface tensiometry, cyclic voltammetry, and UV–vis spectroscopic measurements. The Fc11-4-11Fc solution was found to form highly viscous (˜103 Pa⋅s) TLMs. Unlike the monomeric surfactant, the Fc11-4-11Fc micellar solution maintained its high viscosity even after adding extra builder and/or electrolyte agents. The surface-tensiometric measurements indicate that the effective molecular area of Fc11-n-11Fc at the air/water interface systematically increased with the alkyl spacer length. Using the critical packing parameters estimated with the molecular area, Fc11-4-11Fc is expected to be the most suitable for rod-like micellar growth. Importantly, the viscosity of Fc11-4-11Fc micellar solution could be decreased to that of pure water as a response to electrochemical oxidation reaction, and recovered by the subsequent re-reduction reaction. Hence, the gemini surfactants prepared in this study are a promising class of candidates for potential smart soft material applications.

Synthesis, Spectroscopy, and Redox Studies of Ferrocene-Functionalized Coinage Metal Alkyne Complexes.

Ethynylferrocene (FcC≡CH) was utilized as a redox-active metalloligand for the synthesis of polynuclear coinage metal complexes. The reaction of [FcC≡CLi] with tri- tert-butylphosphine metal chlorides [tBu3P-MCl] (M = Au, Ag, Cu) yielded different heteronuclear ferrocene-funtionalized alkyne complexes featuring metallophilic interactions. Furthermore, the redox properties of the ferrocenyl-functionalized tetracopper complex were investigated by cyclic voltammetry and UV-vis-near-IR spectroelectrochemistry. They indicate the compounds' redox-rich nature and a weak electronic coupling between the redox-active ferrocenyl units over a large distance.

The anionic Fries rearrangement: a convenient route to ortho-functionalized aromatics.

The ortho-directed lithiation of aromatic carbamates and carbonates causes a migration of the substituent from the pendant O group to the adjacent C atom of the aromatic scaffold. This reaction, resulting in the formation of ortho-hydroxycarbonyl compounds, is widely known as the anionic Fries rearrangement, and is described in terms of the migrating group as a 1,3-O→C shift. The intramolecular mechanism allows for a control of regioselectivity by a metalation procedure. Commonly known for the migration of carbonyl groups, the scope has been extended in recent years to Si-, S- and P-based versions, known as the respective anionic sila-, thia- and phospho-Fries rearrangements. Examples of higher homologues, which are sparsely investigated, will also be discussed. Starting with aromatic substrates in the 1980s organometallic backbones, e.g. ferrocenes, have also been introduced, which opened the pathway for stereoselective processes of the Fries rearrangement. Furthermore, related conversions, such as 1,2-, 1,4- (homo-Fries), 1,5- (remote-Fries) and 1,6- as well as, e.g. N→C, and S→C migrations were reported and are included herein. The mechanisms for the Fries rearrangement and competing reactions, e.g. aryne formation, are discussed, based on, e.g., labeling experiments and DFT calculations. Redox-active ferrocenyl derivatives allowed for electrochemical investigations, revealing an influence of the electronic properties of the sandwich unit on the lithiation, rearrangement and post-functionalization behavior of the participating compounds.

New bioactive ferrocene-substituted heteroleptic copper(I) complex: Synthesis, structural elucidation, DNA interaction, and DFT study

In the present work, a new para-ferrocenylbenzoate copper(I) complex (a4) has been synthesized and characterized by numerous spectroscopic techniques such as: FT-IR, AAS, and CHNS analysis. Moreover, the single-crystal X-ray structure of the compound a4 was also explored. The DNA binding potency was determined by cyclic voltammetry, UV-visible spectroscopy, and viscometry. The redox behavior of the complex studied by cyclic voltammetry revealed a single quasi-reversible voltammogram, attributed to the dominant redox-active ferrocenyl moiety. The electrochemical study reveals that the complex binds to DNA non-covalently, the mode of interaction in particular, was found to be an electrostatic. The DNA binding constant was found to be 4.3 × 104 M−1, which is very significant and impressive for non-covalent interactions, and is in close agreement with the UV-visible spectroscopic results. DFT/B3LYP method was used to ascertain the energies of frontier molecular orbitals (HOMO/LUMO) and the charge distribution on the molecular structure. The ferrocene-based copper(I) complex (a4) demonstrated to be a decent candidate in terms of cytotoxicity, although less active than that of the standard chemotherapeutic drug (cisplatin).

Redox-active metal complexes with 2,2′-dipicolylamine containing ferrocenyl moiety: Synthesis, electrochemical behavior and biological activity

The novel metal complexes of general formula MCl2·L (M = Cu, Fe, Co, Mn, Zn) based on the di-(2-picolyl)amine ligand L with the redox-active ferrocenyl fragment were synthesized and characterized by elemental analysis, IR, 1H, 13C NMR, UV–vis spectroscopy and MALDI-TOF mass spectrometry. The molecular structure of [ZnCl2L] was established by X-ray crystallography. The redox properties of complexes were studied using cyclic voltammetry (CV) method and feasible schemes of electrochemical transformations were proposed. The antioxidant activity of compounds was tested by various methods. The lipoxygenase (LOX) inhibition activity of the studied compounds was evaluated. The in vitro biological experiments were performed using rat brain homogenates. The results demonstrate that ditopic compounds containing ferrocene and redox active dipicolylamine fragments act as polyfunctional antioxidants. These results let us to conclude that combining in one molecule several redox-active metal centers is a promising way of metallodrug design in modern medicinal chemistry.

Monosubstituted ferrocene liquid crystals containing click triazole with a wide nematic phase temperature range

ABSTRACTNew monosubstituted ferrocenomesogens of the 1,4-substituted-1,2,3-triazole series 3a-3d and the 5-halogen-1,4-substituted-1,2,3-triazole series 4a-4d were successfully synthesised through a facile and versatile synthetic route using click reactions with moderate yields, in different atmospheres, and catalysed by different amounts of CuX (X = Br, I). Two series of compounds exhibited a typical nematic liquid crystal texture, and the 5-halogen-1,4-substituted-1,2,3-triazole series 4 had a wider mesomorphic temperature range than the corresponding series 3 due to the effect of the halogen atom substituent on the triazole. These compounds showed similar absorption spectra, but the fluorescence emission spectra of 4 were obviously redshift relative to 3. Cyclic voltammetry investigations revealed that the redox-active ferrocenyl groups of 3 and 4 follow one-electron transfer processes.

Colloidal chirality in wormlike micellar systems exclusively originated from achiral species: Role of secondary assembly and stimulus responsivity

Colloidal chirality in wormlike micellar systems exclusively originated from achiral species and discussion of the role of secondary assembly of fiber-like aggregates in chirality generation were presented in this paper. Herein, formation of colloidal wormlike micelles for the first time incorporated chirality and redox-responsiveness into one design via noncovalent interaction. A dual-stimuli-responsive gel of wormlike micelles which were designed by employing a dual-responsive cationic surfactant (FTMA) and a strong gelator (AzoNa4) and regulated by redox reaction and host-guest inclusion is presented. Both the redox and host-guest interaction play an important role in regulating the viscosity and supramolecular chirality of gels of the wormlike micelles. The supramolecular chirality and viscosity of the wormlike micelle gels were switched reversibly by exerting chemical redox onto the ferrocenyl groups. For the amphiphile FTMA containing redox-active ferrocenyl group, reversible control of the oxidation state of ferrocenyl groups leads to the charge and hydrophobicity changes of FTMA, therefore change its self-assembly behavior. Of equal interest, β-CD successfully detached the wormlike micelles via the recognition-inclusion behavior with FTMA and invalidate the H-bond and hydrophobic interaction between FTMA and AzoH4. This designed system provides a new strategy to tune the supramolecular chirality of colloidal aggregates and explore the specific packing mode detail within the micelles or the secondary assembly of the inter-micelles. We anticipate this dual-responsive H-bond-directed chiral gel switch could propose a new strategy when researchers designing new, multi-responsive functional gel materials.

Fabrication of a label-free electrochemical immunosensor using a redox active ferrocenyl dendrimer

An amperometric immunosensor based on a redox active ferrocenyl end-grafted PAMAM dendrimer provides highly sensitive detection of immunoglobulin, down to 2 ng mL−1.

Effects of Ferrocenyl Proximity and Monomer Presence during Oxidation for the Redox-Switchable Polymerization of l-Lactide

A titanium(IV) salfen catalyst bearing a redox-active ferrocenyl center in close proximity to the active metal site was examined for the redox-switchable polymerization of l-lactide. The catalyst displayed an atypical β-cis geometry in both the solid- and solution-states, and placement of the redox-active moiety in close proximity to the active metal site was shown to provide an enhancement in catalytic “on–off–on” switching behavior when the redox events were performed in the presence of lactide monomer. More importantly, when comparing oxidized and reduced catalytic species, completely contrasting trends in polymerization behavior were observed, depending on whether the catalyst was oxidized in the absence or in the presence of lactide monomer. On the basis of NMR spectroscopic analysis, we propose that this unusual behavior is a result of a rapid switch in ligand coordination geometry that is facilitated by monomer coordination prior to any redox reactions. Additionally, when redox reactions were condu...

Electronic modification of redox active ferrocenyl termini and their influence on the electrontransfer properties of 2,5-diferrocenyl-N-phenyl-1H-pyrroles

A series of 2,5-diferrocenyl-N-phenyl-1H-pyrroles of type 2,5-Fc2-cC4H2NPh (Fc = Fe(η5-C5H4)(η5-C5H4R); 3a, R = cC4H7O2; 3b, H; 3c, 3,5-(CF3)2-C6H3) was synthesized by Negishi C,C cross-coupling reactions to connect the heterocyclic unit with the redox active ferrocenyl moieties. The reaction of 3a with p-toluene sulfonic acid gave 3d (R = CHO). A subsequent cyanation reaction of 3d produced 3e (R = CN). Characterization of these molecules was performed by spectroscopic means and single crystal X-ray diffraction analysis (3c–e). It could be shown that the electronic properties of the 2,5-diferrocenyl-N-phenyl-1H-pyrroles is influenced by the substitution of electron withdrawing/donating functional groups in 1′-position of the ferrocenyls. The influence of the electronic nature of the substituents on the charge transfer character of the heterocyclic bridging system was investigated using electrochemical (cyclic and square-wave voltammetry) and spectroelectrochemical methodologies (in situ UV–Vis/NIR spectroscopy). The observed redox splittings ΔE°′ between the redox active ferrocenyls are 390 mV for 3a, 485 mV for 3c, 555 mV for 3d and 600 mV for 3e using [NnBu4][B(C6F5)4] as electrolyte. Furthermore, the electrochemistry studies were performed in [NnBu4][PF6] to determine changes of the electrostatic stabilization. The redox separation increases with increasing electron withdrawing ability of the ferrocenyl substituents in the order R = cC4H7O2 < H < 3,5-(CF3)2-C6H3 < CHO < CN, while the spectroelectrochemical studies reveal decreasing strength of the intramolecular electronic coupling between the iron atoms. All compounds show intense and broad absorptions in the NIR region and can be classified as strongly coupled class II systems according to Robin and Day.

Regulation of charge delocalization in a heteronuclear Fe2 ru system by a stepwise photochromic process.

Heteronuclear complexes FeCp2 -DTE-C≡C-Ru(dppe)2 Cl (1 o; dppe=1,2-bis(diphenylphosphino)ethane, Cp=cyclopentadienyl, DTE=dithienylethene) and FeCp2-DTE-C≡C-Ru(dppe)2-C≡C-DTE-FeCp2 (2 oo), with redox-active ferrocenyl and ruthenium centers separated by a photochromic DTE moiety, were prepared to achieve photoswitchable charge delocalization and Fe⋅⋅⋅Ru electronic communication. Upon UV-light irradiation of 2 oo, the Fe⋅⋅⋅Ru heterometallic electronic interaction is increasingly facilitated with stepwise photocyclization, 2 oo→2 co→2 cc; this is ascribed to the gradual increase in π-conjugated systems. The near-infrared absorptions in mixed-valence species [2 oo](+) /[2 co](+) /[2 cc](+) are gradually intensified following the conversion of [2 oo](+) →[2 co](+) →[2 cc](+) , which demonstrates that the extent of charge delocalization shows progressive enhancement with stepwise photocyclization. As revealed by electrochemical, spectroscopic, and theoretical studies, complex 2 exhibits nine switchable states through stepwise photochromic and reversible redox processes.

A zinc(II) tetraphenylporphyrin peripherally functionalized with redox-active “trans-[(η5-C5H5)Fe(η5-C5H4)C[tbnd]C](κ2-dppe)2Ru(C[tbnd]C)-” substituents: Linear electrochromism and third-order nonlinear optics

A nonametallic organometallic-coordination complex (4), assembled from redox-active ferrocenyl (Fc) and Ru(κ2-dppe)2 fragments (dppe=1,2-bis(diphenylphosphino)ethane) as peripheral donor groups and a central Zn(II) tetraphenylporphyrin (ZnTPP) core, has been prepared and characterized. Complex 4 is obtained in one step from a pentametallic organometallic porphyrin precursor following substitution of the peripheral chloride ligands by ferrocenylalkynyl moieties (CCFc). The spectroelectrochemistry of 4, and that of previously reported porphyrins featuring related peripheral electron-rich d6-transition metal alkynyl units, has been investigated; the optical and redox properties of 4 are briefly discussed, and its potential, and that of a related pentanuclear tetraferrocenyl ZnTPP complex, to function as redox-switchable chromophores is examined. Preliminary studies of the cubic NLO properties of 4 have been undertaken by Z-scan studies at 560nm and 630nm, the results from which are also reported.

A rhodium(I) dicarbonyl complex with a redox-active ferrocenyl phosphine-NHC ligand: Enhanced reactivity of the metal centre through ferrocene oxidation

A rhodium(I) dicarbonyl complex bearing a bidentate ferrocenyl phosphine-NHC ligand has been synthesized and characterized by NMR, IR spectroscopy, mass spectrometry and X-ray diffraction methods. Its behaviour towards oxidation was investigated and revealed that changing the oxidation state of ferrocene can significantly modify the electron density at rhodium. Oxidation of the rhodium(I) dicarbonyl complex in acetonitrile furnished an air-stable rhodium(III) complex, stabilized by acetonitrile molecules and with an interesting C–H bond activation at ferrocene. This new rhodium(III) complex is active for the hydrosilylation of acetophenone and its derivatives.

One-dimensional Anisotropic Metal–Organic Module Containing a Pt6 Chain Terminated with Redox Active Ferrocenyl Units

Abstract A 1D anisotropic hexaplatinum chain with redox-active terminal ligands, [Pt6(µ-H)(µ-dpmp)4(FcDipNC)2](PF6)3 (7) (dpmp: bis(diphenylphosphinomethyl)phenylphosphine, FcDipNC: 2,6-diisopropyl-4-(ferrocenylethynylene)phenyl isocyanide), was synthesized, its structure and electrochemical behavior were elucidated in comparison with those of [Pt6(µ-H)(µ-dpmp)4(DipNC)2](PF6)3 (6) (DipNC: 2,6-diisopropylphenyl isocyanide), and the module was found to undergo two stepwise two-electron oxidations.

Hexanuclear Gold(I) Phosphide Complexes as Platforms for Multiple Redox-Active Ferrocenyl Units

The synthesis, X-ray crystal structures, electrochemical, and spectroscopic studies of a series of hexanuclear gold(I) μ(3)-ferrocenylmethylphosphido complexes stabilized by bridging phosphine ligands, [Au(6)(P-P)(n)(Fc-CH(2)-P)(2)][PF(6)](2) (n=3, P-P=dppm (bis(diphenylphosphino)methane) (1), dppe (1,2-bis(diphenylphosphino)ethane) (2), dppp (1,3-bis(diphenylphosphino)propane) (3), Ph(2)PN(C(3)H(7))-PPh(2) (4), Ph(2)PN(Ph-CH(3)-p)PPh(2) (5), dppf (1,1′-bis(diphenylphosphino)ferrocene) (6); n=2, P-P=dpepp (bis(2-diphenylphosphinoethyl)phenylphosphine) (7)), as platforms for multiple redox-active ferrocenyl units, are reported. The investigation of the structural changes of the clusters has been probed by introducing different bridging phosphine ligands. This class of gold(I) μ(3)-ferrocenylmethylphosphido complexes has been found to exhibit one reversible oxidation couple, suggestive of the absence of electronic communication between the ferrocene units through the Au(6)P(2) cluster core, providing an understanding of the electronic properties of the hexanuclear Au(I) cluster linkage. The present complexes also serve as an ideal system for the design of multi-electron reservoir and molecular battery systems.