Oxidation‐Triggered Ring‐Opening Metathesis Polymerization

Eight new N‐Hoveyda‐type complexes were synthesized in yields of 67–92 % through reaction of [RuCl₂(NHC)(Ind)(py)] (NHC=1,3‐bis(2,4,6‐trimethylphenylimidazolin)‐2‐ylidene (SIMes) or 1,3‐bis(2,6‐diisopropylphenylimidazolin)‐2‐ylidene (SIPr), Ind=3‐phenylindenylid‐1‐ene, py=pyridine) with various 1‐ or 1,2‐substituted ferrocene compounds with vinyl and amine or imine substituents. The redox potentials of the respective complexes were determined; in all complexes an iron‐centered oxidation reaction occurs at potentials close to E=+0.5 V. The crystal structures of the reduced and of the respective oxidized Hoveyda‐type complexes were determined and show that the oxidation of the ferrocene unit has little effect on the ruthenium environment. Two of the eight new complexes were found to be switchable catalysts, in that the reduced form is inactive in the ring‐opening metathesis polymerization of cis‐cyclooctene (COE), whereas the oxidized complexes produce polyCOE. The other complexes are not switchable catalysts and are either inactive or active in both reduced and oxidized states.     

Ferrocene–β‐Cyclodextrin Conjugates: Synthesis,Supramolecular Behavior,and Use as Electrochemical Sensors

Ferrocene with a β‐cyclodextrin unit bound to one or both cyclopentadienyl rings through the secondary face were conveniently synthesized by regiospecific copper(I)‐catalyzed cycloaddition of 2‐O‐propargyl‐β‐cyclodextrin to azidomethyl or bis(azidomethyl)ferrocene. The supramolecular behavior of the synthesized conjugates in both the absence and presence of bile salts (sodium cholate, deoxycholate, and chenodeoxycholate) was studied by using electrochemical methods (cyclic and differential pulse voltammetry), isothermal titration calorimetry, and NMR spectroscopy (PGSE, CPMG, and 2D‐ROESY). These techniques allowed the determination of stability constants, mode of inclusion, and diffusion coefficients for complexes formed with the neutral and, in some cases, the oxidized states of the ferrocenyl conjugates. It was found that the ferrocenyl conjugate with one β‐cyclodextrin unit forms a redox‐controllable head‐to‐head homodimer in aqueous solution. The ferrocene–bis(β‐cyclodextrin) conjugate is present in two distinguishable forms in aqueous solution, each one having a different half‐wave oxidation potential for the oxidation of the ferrocene. By contrast, only one distinguishable form for the oxidized state of the ferrocene–β‐cyclodextrin conjugate is detectable. The redox‐sensing abilities of the synthesized conjugates towards the bile salts were evaluated based on the observed guest‐induced changes in both the half‐wave potential and the current peak intensity of the electroactive moiety.     

Multi‐Stimuli‐Responsive Organometallic Gels Based on Ferrocene‐Linked Poly(Aryl Ether) Dendrons: Reversible Redox Switching and Pb2+‐Ion Sensing

We describe the design, synthesis, and “stimuli‐responsive” study of ferrocene‐linked Fréchet‐type [poly(aryl ether)]‐dendron‐based organometallic gels, in which the ferrocene moiety is attached to the dendron framework through an acyl hydrazone linkage. The low‐molecular‐weight gelators (LMWGs) form robust gels in both polar and non‐polar solvent/solvent mixtures. The organometallic gels undergo stimuli‐responsive behavior through 1) thermal, 2) chemical, and 3) electrochemical methods. Among them, conditions 1 and 3 lead to seamlessly reversible with repeated cycles of identical efficiency. Results indicate that the flexible nature of the poly(aryl ether) dendron framework plays a key role in retaining the reversible electrochemical behavior of ferrocene moiety in the LMWGs. Further, the organometallic gelators have exhibited unique selectivity towards Pb²⁺ ions (detection limit ≈10^?8 M ). The metal ion‐sensing results in a gel–sol phase transition associated with a color change visible to the naked eye. Most importantly, decomplexing the metal ion from the system leads to the regeneration of the initial gel morphology, indicating the restoring ability of the organometallic gel. The metal–ligand binding nature has been analyzed by using ¹H NMR spectroscopy, mass spectrometry, and DFT calculations.     

The synthesis,characterization and polycondensation of metal‐containing diols: crystal structure of [(η5‐C5H5)(CO)2Fe(CH2)3O‐{2,6‐(CH2OH)2‐4‐CH3?C6H2}]

The synthesis of two new transition‐metal‐containing polyesters is described. The precursors are bifunctional organometallic monomers that were synthesized using 2,6‐bis(hydroxymethyl)‐p‐cresol as the key reagent. This was achieved by simple coupling reactions between the appropriate organometallic alkyl halide and the cresol reagent. Polycondensation reactions were carried out with terephthaloyl chloride using ambient temperature solution techniques. The new low molecular weight oligomeric polyesters were characterized using Fourier transform infrared and ¹HNMR spectroscopy, differential scanning calorimetry, thermogravimetric analysis and size‐exclusion chromatography analyses. Copyright © 2002 John Wiley & Sons, Ltd.     

Ferrocenophanes with Interannular Nitrogen–Gallium Bridges. 1,3,2‐Diazagalla‐[3]Ferrocenophanes and an 1‐Aza‐3‐Azonia‐2‐Gallata‐[3]Ferrocenophane. Synthesis and Structure

1,1′‐Bis(trimethylsilylamino)ferrocene reacts with trimethyl‐ and triethylgallium to give the μ‐[ferrocene‐1,1′‐diyl‐bis(trimethylsilylamido)]tetraalkyldigallanes. These were converted into the 1,3‐bis(trimethylsilyl)‐2‐alkyl‐2‐pyridine‐1,3,2‐diazagalla‐[3]ferrocenophanes, of which the ethyl derivative was characterized by X‐ray structural analysis. Treatment of gallium trichloride with N,N′‐dilithio‐1,1′‐bis(trimethylsilylamino)ferrocene affords μ‐[ferrocene‐1,1′‐diyl‐bis(trimethylsilylamido)]tetrachlorodigallane along with bis(trimethylsilyl)‐2,2‐dichloro‐1‐aza‐3‐azonia‐2‐gallata‐[3]ferrocenophane as a side product, and both were structurally characterized by X‐ray analysis. The solution‐state structures of the new gallium compounds and aspects of their molecular dynamics in solution were studied by NMR spectroscopy (¹H, ¹³C, ²⁹Si NMR).     

Asymmetric Mixed‐Valence Complexes that Consist of Cyclometalated Ruthenium and Ferrocene: Synthesis,Characterization, and Electronic‐Coupling Studies

Three bis‐tridentate ferrocene‐containing cyclometalated ruthenium complexes, [(Fcdpb)Ru(tpy)]⁺ ( 1 ⁺), [(Fctpy)Ru(dpb)]⁺ ( 2 ⁺), and [(Fcdpb)Ru(Fctpy)]⁺ ( 3 ⁺), have been prepared and characterized, where Fcdpb is the 2‐deprotonated form of 1,3‐di(2‐pyridyl)‐5‐ferrocenylbenzene, tpy is 2,2′:6′,2“‐terpyridine, dpb is the 2‐deprotonated form of 1,3‐di(2‐pyridyl)benzene, and Fctpy is 4′‐ferrocenyl‐2,2′:6′,2”‐terpyridine. Single crystals of compounds 2 ⁺ and 3 ⁺ have been studied by X‐ray analysis. Complexes 1 ⁺ and 2 ⁺ displayed two anodic redox waves, whilst three well‐separated redox couples were observed for compound 3 ⁺. A combined experimental and computational study suggested that the ferrocene unit on the Fcdpb moiety in compounds 1 ⁺ and 3 ⁺ was oxidized first. In contrast, the order of the oxidation of ruthenium and ferrocene in complex 2 ⁺ was reversed. Metal‐to‐metal‐charge‐transfer transitions (MM′CT) have been observed for the singly oxidized states 1 ²⁺, 2 ²⁺, and 3 ²⁺ in the near‐infrared region. Hush analysis showed that the metal–metal electronic couplings in compounds 1 ²⁺ and 3 ²⁺ were much stronger than those in compound 2 ²⁺.     

Ligand‐Promoted Oxidative Cross‐Coupling of Aryl Boronic Acids and Aryl Silanes by Palladium Catalysis

The first cross‐coupling reaction between aryl silanes and aryl boronic acids is described. This transformation represents one of the very few examples of coupling reactions between two nucleophilic organometallic reagents and provides a new method for the formation of biaryl compounds. The successful development of this reaction was enabled by the use of commercially available 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (BINAP) as the ligand. A small amount of BINAP (3 mol %) was sufficient to suppress the formation of the homocoupling products, and the reaction yielded the cross‐coupling products with high selectivity under mild conditions, even when the ratio of the two coupling partners was 1:1.     

Rhodium(III)‐Catalyzed ortho‐Heteroarylation of Phenols through Internal Oxidative CH Activation: Rapid Screening of Single‐Molecular White‐Light‐Emitting Materials

Reported herein is the first example of a transition‐metal‐catalyzed internal oxidative C? H/C? H cross‐coupling between two (hetero)arenes through a traceless oxidation directing strategy. Without the requirement of an external metal oxidant, a wide range of phenols, including phenol‐containing natural products, can undergo the coupling with azoles to assemble a large library of highly functionalized 2‐(2‐hydroxyphenyl)azoles. The route provides an opportunity to rapidly screen white‐light‐emitting materials. As illustrative examples, two bis(triphenylamine)‐bearing 2‐(2‐hydroxyphenyl)oxazoles, which are difficult to access otherwise, exhibit bright white‐light emission, high quantum yield, and thermal stability. Also presented is the first example of the white‐light emission, in a single excited‐state intramolecular proton transfer system, of 2‐(2‐hydroxyphenyl)azoles, thus highlighting the charm of C? H activation in the discovery of new organic optoelectronic materials.     

Ferrocene‐Promoted Long‐Cycle Lithium–Sulfur Batteries

Confining lithium polysulfide intermediates is one of the most effective ways to alleviate the capacity fade of sulfur‐cathode materials in lithium–sulfur (Li–S) batteries. To develop long‐cycle Li–S batteries, there is an urgent need for material structures with effective polysulfide binding capability and well‐defined surface sites; thereby improving cycling stability and allowing study of molecular‐level interactions. This challenge was addressed by introducing an organometallic molecular compound, ferrocene, as a new polysulfide‐confining agent. With ferrocene molecules covalently anchored on graphene oxide, sulfur electrode materials with capacity decay as low as 0.014 % per cycle were realized, among the best of cycling stabilities reported to date. With combined spectroscopic studies and theoretical calculations, it was determined that effective polysulfide binding originates from favorable cation–π interactions between Li⁺ of lithium polysulfides and the negatively charged cyclopentadienyl ligands of ferrocene.     

The Marriage of Peripherally Metallated and Directly Linked Porphyrins: Bromidobis(phosphine)platinum(II) as a Cation‐Stabilizing Substituent on Directly Linked and Fused Triply Linked Diporphyrins

A meso‐bromidoplatiniobis(triphenylphosphine) η¹‐organometallic porphyrin monomer was prepared by the oxidative addition of meso‐bromoZnDPP (DPP=dianion of 5,15‐diphenylporphyrin) to a platinum(0) species. The meso–meso directly linked dimeric porphyrin ( 5 ) was prepared from this monomer by silver(I)‐promoted oxidative coupling and planarized to give a triply linked dizinc(II) porphyrin dimer ( 8 ). Acidic demetallation of 8 afforded the bis(free base) 9 . Dimer 5 was demetallated then remetallated with nickel(II) to give the dinickel(II) analogue 10 , the X‐ray crystal structure of which showed a twisted molecule with ruffled, orthogonal NiDPP rings, terminated by square‐planar trans‐[Pt(PPh₃)₂Br] units. New compounds were fully characterized spectroscopically, and the fused diporphyrin exhibited a broad, low‐energy, near‐IR electronic absorption band near 1100 nm. Electrochemical measurements of this series indicate that the organometallic fragment is a strong electron donor towards the porphyrin ring. The triply linked organometallic diporphyrin has a substantially lowered first one‐electron oxidation potential (?0.35 V versus the ferrocene/ferrocenium couple (Fc/Fc⁺)) and a narrow HOMO–LUMO gap of 0.96 V. Solutions prepared for NMR spectroscopy slowly decompose with degradation of the signals, which is attributed to partial oxidation to the cation radical. This paramagnetic species can be reduced in situ by hydrazine to restore the NMR spectrum to its former appearance. The combined influence of the two [Pt(PPh₃)₂Br] electron‐donating substituents is sufficient to make dimer 5 too aerobically unstable to allow further elaboration.     

Reaktionsverhalten verschiedener Carbodiimide mit Ferrocen‐1, 1'‐dicarbonsäure

Reaction Behaviour of Several Carbodiimides with 1, 1'‐Ferrocenedicarboxylic Acid 1, 1'‐bis‐(1, 3‐dicyclohexylureidocarbonyl)‐ferrocene ( 1 ), 1, 1'‐bis‐(1, 3‐diisopropylureidocarbonyl)‐ferrocene ( 2 ) and ferrocene‐1, 1'‐bis‐N‐p‐tolylcarboxamide ( 6 ) were synthesized by melting down 1, 1'‐ferrocenedicarboxylic acid ( 7 ) together with N, N'‐dicyclohexylcarbodiimide (DCC), N, N'‐diisopropylcarbodiimide (DIC) or N, N'‐di‐p‐tolylcarbodiimide ( 8 ), respectively, without application of any solvent in a short space of time. Substance 1 , 2 , 1, 1'‐bis‐(1‐ethyl‐3‐tert‐butylureidocarbonyl)‐ferrocene ( 3 ), 1‐(1‐tert‐butyl‐3‐ethylureidocarbonyl)‐1'‐(1‐ethyl‐3‐tert‐butylureidocarbonyl)‐ferrocene ( 4 ) and 1, 1'‐bis‐(1‐tert‐butyl‐3‐ethylureidocarbonyl)‐ferrocene ( 5 ) were obtained in good yield by reacting 7 DCC, DIC, or N‐tert‐butyl‐N'‐ethylcarbodiimide ( 9 ), respectively, with in ethyl acetate for weeks. Transannular 1, 1'‐ferrocenedicarboxylic anhydride was not detectable or isolable in these reactions. All new compounds were characterized by ¹H‐NMR, ¹³C‐NMR, IR, MS and elementar analysis. In the case of 1 a single crystal structure analysis was made.     

Attachment of Amine‐ and Maleimide‐Containing Ferrocene Derivatives onto Self‐Assembled Alkanethiol and Alkanedithiol Monolayers: Voltammetric Evaluation of Cross‐Linking Efficiencies and Surface Coverage of Electroactive Groups

Ferrocene derivatives containing primary amines and maleimide groups were attached covalently onto N‐hydrosuccinimidyl (NHS)‐terminated alkanethiol self‐assembled monolayers (SAMs) and SAMs of alkanedithiol. The surface coverage and efficiencies of the two cross‐linking reactions were evaluated with cyclic voltammetry. All the ferrocene derivatives attached onto the alkanethiol or alkanedithiol SAMs exhibit reversible redox waves. The surface coverage of the aminated ferrocene groups was compared to that of N‐hydrosuccinimidyl (NHS)‐terminated alkanethiol SAM. The covalent attachment of β‐ferrocenylethylamine onto a 11,11′‐dithio‐bis(succinimidylundecanoate) SAM yielded an efficiency as high as 63.1%. The cross‐linking efficiency of this reaction was found to increase with the nucleophilicity of the amino groups. SAMs of longer alkyl chains favor the attachment of a greater number of ferrocene derivatives. As for the Michael‐type electrophilic addition between the sulfhydryl groups of the alkanedithiol SAMs and the ferrocenyl maleimide, the cross‐linking efficiencies were found to range from 6.5% to 25.7%, depending on the alkanedithiol chain length. The difference in the efficiencies between the two types of cross‐linking reactions might be partially attributable to the steric hindrance imposed by the SAMs and the relative sizes of the functional groups.     

Synthesis,Properties, and Redox Behavior of 1,1,4,4‐Tetracyano‐2‐ferrocenyl‐1,3‐butadienes Connected by Aryl,Biaryl, and Teraryl Spacers

Aryl‐substituted 1,1,4,4‐tetracyano‐1,3‐butadienes (FcTCBDs) and bis(1,1,4,4‐tetracyanobutadiene)s (bis‐FcTCBDs), possessing a ferrocenyl group on each terminal, were prepared by the reaction of a variety of alkynes with tetracyanoethylene (TCNE) in a [2+2] cycloaddition reaction, followed by retro‐electrocyclization of the initially formed [2+2] cycloadducts (i.e., cyclobutene derivatives). The characteristic intramolecular charge transfer (ICT) between the donor (ferrocene) and acceptor (TCBD) moieties were investigated by using UV/Vis spectroscopy. The redox behaviors of FcTCBDs and bis‐FcTCBDs were examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed their properties of multi‐electron transfer depending on the number of ferrocene and TCBD moieties. Moreover, significant color changes were observed by visible spectroscopy under the electrochemical reduction conditions.     

Synthesis,characterization, coordination and antibacterial properties of novel asymmetric 1,1′‐disubstituted ferrocene‐derived Schiff‐base ligands and their Co(II), Cu(II) Ni(II) and Zn(II) complexes

Some new asymmetric 1,1 ′‐disubstituted ferrocene‐derived Schiff‐bases have been prepared and used as ligands in the preparation of their Co(II), Cu(II), Ni(II) and Zn(II) metal chelates. These synthesized ligands and their metal chelates have been characterized by their physical, analytical and spectral data. These have also been used for screening against pathogenic bacterial species, e.g. Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Klebsiella pneumonae and have been found to be a novel class of organometallic‐based antibacterials. Copyright © 2001 John Wiley & Sons, Ltd.     

N‐Heterocyclic Carbenes: A New Concept in Organometallic Catalysis

N‐Heterocyclic carbenes have become universal ligands in organometallic and inorganic coordination chemistry. They not only bind to any transition metal, be it in low or high oxidation states, but also to main group elements such as beryllium, sulfur, and iodine. Because of their specific coordination chemistry, N‐heterocyclic carbenes both stabilize and activate metal centers in quite different key catalytic steps of organic syntheses, for example, C−H activation, C−C, C−H, C−O, and C−N bond formation. There is now ample evidence that in the new generation of organometallic catalysts the established ligand class of organophosphanes will be supplemented and, in part, replaced by N‐heterocyclic carbenes. Over the past few years, this chemistry has been the field of vivid scientific competition, and yielded previously unexpected successes in key areas of homogeneous catalysis. From the work in numerous academic laboratories and in industry, a revolutionary turning point in oraganometallic catalysis is emerging.     

Concerted and Stepwise Mechanisms in Metal‐Free and Metal‐Assisted [4+3] Cycloadditions Involving Allyl Cations

The thermal [4+3] cycloaddition reaction between allenes and tethered dienes (1,3‐butadiene and furan) assisted by transition metals (Au^I, Au^III, Pd^II, and Pt^II) was studied computationally within the density functional theory framework and compared to the analogous non‐organometallic process in terms of activation barriers, synchronicity and aromaticity of the corresponding transition states. It was found that the metal‐mediated cycloaddition reaction is concerted and takes place via transition structures that can be even more synchronous and more aromatic than their non‐organometallic analogues. However, the processes exhibit slightly to moderately higher activation barriers than the parent cycloaddition involving the hydroxyallylic cation. The bond polarization induced by the metal moiety is clearly related to the interaction of the transition metal with the allylic π* molecular orbital, which constitutes the LUMO of the initial reactant. Finally, replacement of the 1,3‐butadiene by furan caused the transformation to occur stepwise in both the non‐organometallic and metal‐assisted processes.     

Ruthenium‐Grafted Vinylhelicenes: Chiroptical Properties and Redox Switching

The properties of mono‐ and bis‐Ru–vinyl[6]helicene complexes ( 2 a and 2 b , respectively), recently synthesized by using molecular engineering of helicenes based on the grafting of lateral organometallic substituents on the π‐helical backbone through a vinyl bridge, are presented. These helicene derivatives are thoroughly characterized, with special attention given to their chiroptical properties and redox switching activity. The UV/Vis and electronic circular dichroism (ECD) spectra of P and M enantiopure species, both in the neutral and oxidized states ([ 2 a ] ^{. +}, [ 2 b ] ^{. +}, and [ 2 b ]²⁺), are analyzed with the aid of quantum‐chemical calculations. The extended π‐conjugation facilitated by the vinyl moiety, clearly visible in the electronic structures of 2 a , b , introduces new active bands in the ECD spectra that consequently lead to a significant increase in optical rotation of Ru–vinylhelicenes compared with the organic precursors. The vibrational circular dichroism (VCD) spectra were measured and calculated for both the organic and organometallic species and constitute the first examples of VCD for metal‐based helicene derivatives. Finally, the redox‐triggered chiroptical switching activity of 2 a , b is examined in detail by using ECD spectroscopy. The modifications of the ECD spectra in the UV/Vis and NIR region are well reproduced and rationalized by calculations.     

Miscellaneous applications of ferrocene‐based peptides/amides

This article provides a critical review of the different applications of ferrocene‐based peptides/amides in biological as well as in non‐biological systems. Ferrocene‐based peptides/amides find many applications in different fields such as materials science, medicine, organic synthesis, bio‐organometallic and biological chemistry, asymmetric catalysis, nonlinear optics, in polymer science as redox active polymers and dendrimers, in molecular recognition as biosensors and in electrochemistry). Extensive research is being done on ferrocene‐based peptides/amides but we will highlight the various applications of ferrocene‐based peptides/amides for the period 2006–2010. The main factors that govern the potential biological and non‐biological applications are an electroactive core, a conjugated linker that can act as a chromophore and lower the oxidation potential of the ferrocene part, an amino acid or peptide derivative that can interact with other molecules via hydrogen bonding or any secondary bonding, and symmetric and asymmetric substitution on the ferrocene moiety. Copyright © 2011 John Wiley & Sons, Ltd.     

Main chain 1,1′‐ferrocene‐containing polyelectrolytes exhibiting thermotropic liquid‐crystalline and fluorescent properties

A series of 1,1′‐ferrocene‐containing polyelectrolytes ( 3, 4 ) were prepared when 1,1′‐bis(N,N‐dimethylaminomethyl)ferrocene ( 1a ) or 1, 1′‐bis{[1‐(2‐methyl)imidazol‐1‐yl]methyl}ferrocene ( 1b ) was quaternized with 1,4‐dibromobutane or α, α′‐dibromo‐p‐xylene. The counterion was bromide or bis(trifluoromethanesulfonyl)‐amide formed after metathesis with the lithium salt. Their chemical structures were determined by IR and NMR spectra. Molecular weights in the range of ～5400 ( 4a )– ～14,700 ( 4c ) for number‐average molecular weights (M_n) over narrow molecular weight distributions were determined for polymers 4 by gel permeation chromatography. Thermal properties of these materials were obtained by differential scanning calorimetry and thermogravimetric analysis that showed the polymers had thermal stabilities ranging between 172 and 330 °C. Liquid‐crystalline behavior was investigated on a hot stage polarizing optical microscope. Polymers 3a , 4b , and 4d formed either a high‐order or a low‐order smectic phase above their melting or fusion temperatures, and exhibited smectic‐to‐isotropic transitions. The ranges of the liquid‐crystalline phases for these materials were 22, 46, and >55 °C. Compounds 3b , 4a , and 4c are crystalline before melting or decomposing. All of the polymers exhibited absorption bands at ～430 nm. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 974–983, 2005     

Kristallstrukturen ferrocenhaltiger 1,3‐Diketon‐ und Enaminoketon‐Derivate

Crystal Structures of 1,3‐Diketone and Enaminoketone Derivatives Containing Ferrocene The crystal structures of the 1,3‐diketones 2,4‐dioxo‐4‐ferrocenyl‐butanoic acid ethylester ( 1 ) und ferrocene‐1,1′‐bis(2,4‐dioxo‐butanoic acid ethylester) ( 2 ) have been determined. Through conversion of 1 by Cu(ac)₂ · H₂O in THF the copper(II) complex aqua‐bis(3‐ethoxycarbonyl‐1‐ferrocenyl‐propane‐1,3‐dionato) copper(II) ( 1 a ) has been obtained, which is structurally characterized too. The structures of the enaminoketones 2,2′‐(1,4‐phenylenediamino)‐bis(4‐ferrocenyl‐4‐oxo‐but‐2‐enoic acid ethylester) ( 3 ) and ferrocene‐1,1′‐bis(4‐oxo‐2‐phenylamino‐but‐2‐enoic acid ethylester) ( 4 ) have been determined by X‐ray analysis as well. Electrochemical studies completed the structural investigations.