Novel ferrocenyl nitroxides: Synthesis, structures, electrochemistry and antioxidative activity

Novel ferrocenyl nitroxides 3−6 were prepared as models for studying the linkage structure-activity relationship. Single-crystal X-ray structures of compounds 4 and 5 were determined and comparatively studied. The in vitro antioxidative activities (e.g. scavenging superoxide anion and hydroxide radical) of compounds 3−6 and 4-ferrocenamido-2,2,6,6-tetramethyl-piperidin-oxy (2) were evaluated. Compounds 3 and 5 exhibit high scavenging activities in low concentration. Results from electrochemistry and UV/Vis spectroscopy show that the redox property and antioxidative activity are closely related to the structure of the linkage bridging ferrocene and cyclic nitroxide moieties. The results further indicate that the ferrocene moiety plays a principal role in antioxidation. The modification of linkage was found to be able to decrease the ferrocene/ferrocenium potential and improve the antioxidative activity effectively.     

Synthesis, properties and crystal structures of ferrocene derivatives containing pyrazinium and quinoxalinium units

The pyrazinium salt [FcCH₂pyz][BF₄] (1) and the quinoxalinium salt [FcCH₂quin][BF₄] (2) were prepared by the reaction of [FcCH₂][BF₄] with pyrazine and quinoxaline, respectively and characterised by spectroscopic methods, cyclic voltammetry and by single-crystal X-ray diffraction, which revealed the absence of any π-π-stacking motifs in the crystal structures.     

Synthesis, structure, electrochemistry and ROMP-activity of new ferrocenyl analog of Grubbs’ metathesis catalyst

Treatment of [(PCy₃)₂Cl₂RuCH-Ph] (I) with vinylferrocene 1 and 1-ferrocenyl-1,3-butadiene 2 yielded solid products. These new complexes were characterized by ¹H NMR, ³¹P NMR and ¹³C NMR spectroscopy. X-ray crystal structures of both the complexes have been solved. The crystal structure of II confirmed the assigned structure and revealed existence of two sets of intermolecular C-H-Cl(M) type interactions, viz. (Ru)Cl-H-C(ferrocene) and (Ru)Cl-H-CHCl₂. The air-stable, dark solid II is an efficient catalyst for ring-opening metathesis polymerization (ROMP) of cyclopentene, norbornene and cycloocta-1,5-diene. Electrochemical behavior of the complexes clearly reflects electronic communication between two metal centers.     

Synthesis,crystal structure,spectroscopy, and electrochemistry of a uranium complex

A uranium coordination compound with pyridine-2,6-dicarboxylic acid in deionized water has been synthesized and characterized by IR, UV, XPS, and X-ray single-crystal diffraction. The crystal belongs to the monoclinic system, space group C2/c with a?=?1.8427(4)?nm, b?=?0.6886(16)?nm, c?=?1.5442(4)?nm, α?=?90°, β?=?94.082(2)°, γ?=?90°, Z?=?4, and V?=?1.9544(8)?nm³. The structure shows an eight-coordinate uranium forming a hexagonal bi-pyramidal 3-D geometry with pyridine-2,6-dicarboxylate as building units. Fluorescent studies show several strong emissions. Cyclic voltammetric measurement of the compound reveals that uranium(VI) is reduced irreversibly at E _1/2?=?927?mV with ΔE _p?=?77?mV, E _1/2?=??289?mV with ΔE _p?=?113?mV. The electron transfer number (n) involved in reduction processes could be calculated to be approximately two and one, which corresponded to the unusual U(VI)/U(IV) and U(IV)/U(III) couples.     

Platinum (II) phosphine complexes with acetylene ligands containing 1,4,5,8-naphthalenediimide: Synthesis, crystal structure and electrochemistry

A new acetylene ligand modified with the electron-accepting 1,4,5,8-naphthalenediimide group and its Pt(II) phosphine complexes are reported. The Pt(II) complexes incorporate optical properties of the imide group, and display two reversible imide-centred reduction processes.     

Synthesis, structure and redox potentials of biologically active ferrocenylalkyl azoles

The syntheses, structures, electrochemical properties of the series of ferrocenylalkyl azoles, FcAlkAz, as well as the antitumor activity of ferrocenylmethyl benzimidazole (8) have been studied. Above mentioned compounds were investigated by the method of cyclic voltametry. All of them exhibited a reversible one-electron oxidation-reduction wave owing to the ferrocene-ferrocenium redox couple with a positive shift (0.50-0.65 V) compared with that of ferrocene (0.42 V). The X-ray determination of molecular structures of 1-(ferrocenylmethyl)imidazole (4), 1-(ferrocenylbenzyl)imidazole (7) and 1-(ferrocenylmethyl)bezimidazole (8) was carried out. Compound 4 with imidazolyl substituent was found to be present in N-protonated form. Antitumor activity of 1-(ferrocenylmethyl)benzimidazole (8) against some solid tumor models such as adenocarcinoma 755 (Ca755), melanoma B16 (B16) and Lewis lung carcinoma was studied. The antitumor activity of compound 8 was compared with cisplatin effectiveness against some experimental tumor systems.     

Synthesis, characterization, and electrochemistry of tetracarbonyl(6-ferrocenyl-2,2′-bipyridine)tungsten(0)

6-Ferrocenyl-2,2′-bipyridine (fcbpy) was prepared by the reaction of lithiated ferrocene with bipyridine and employed as a bidentate ligand for the formation of tetracarbonyl(6-ferrocenyl-2,2′-bipyridine)tungsten(0). The labile complex pentacarbonyl[η²-bis(trimethylsilyl)ethyne]tungsten(0) reacts with fcbpy in CH₂Cl₂ to yield the disubstitution product, W(CO)₄(fcbpy), which was isolated as analytically pure substance and characterized by elemental analysis, IR, UV-Vis, MS, ¹H and ¹³C NMR spectroscopies. Electrochemistry of the fcbpy molecule and its complex W(CO)₄(fcbpy) was studied by cyclic voltammetry and controlled potential electrolysis combined with UV-Vis spectrometer. In the cyclic voltammogram of both the fcbyp molecule and its complex, an irreversible reduction and a reversible oxidation are assigned to the bipyridine and ferrocene moieties, respectively. The W(CO)₄(fcbpy) complex exhibits additionally two irreversible oxidations due to the tungsten centered electron transfer reactions.     

Rhodium(III) and iridium(III) complexes of thioarylazoimidazoles: Synthesis,structure, spectral characterization,electrochemistry and DFT calculation

[M(SRaaiNR′)Cl₃] (M = Rh(III), Ir(III) and SRaaiNR′ = 1-alkyl-2-{(o-thioalkyl)phenylazo}imidazole) complexes are described in this article. The single crystal X-ray structure of one of the complexes, [Rh(SMeaaiNEt)Cl₃] (3b), shows a tridentate chelation of SMeaaiNEt via N(imidazole), N(azo) and S(thioether) donor centres. Spectral characterization has been done by IR, UV–Vis and ¹H NMR data. The electronic structure, redox properties and spectra are well supported by DFT and TDDFT computation on the complexes.     

Synthesis, electrochemistry and metal binding properties of monosubstituted ferrocenoyl peptides with thioether-containing sidechains

Ferrocenoyl peptides incorporating thioether functionality respond more strongly to mercury(II) than to other heavy metal ions in solution. Compounds reported previously in this context are all 1,1′-disubstituted, and all include two or more sulfur-containing amino acids. To test whether two thioether groups are required for effective mercury binding by these systems, we have prepared a series of singly-substituted ferrocenoyl peptides from ferrocenecarboxylic acid and l-methionine, S-methyl-l-cysteine or S-trityl-l-cysteine, and tested them as electrochemical probes for mercury(II). Nine ferrocenoyl peptides have been synthesised using a Boc-protecting group strategy and HBTU-mediated peptide coupling. The electrochemical properties of these compounds have been determined using cyclic voltammetry, and all show fully reversible one electron oxidation steps. Forward sweep half wave peaks (E_F), reverse sweep half wave peaks (E_R), peak separations (ΔE_P) and half wave potentials (E_1/2) are reported. Changes in the potential of the iron(II)/iron(III) redox couple of the ferrocene core have been used to quantify heavy metal-peptide interactions, revealing that these monotopic systems also respond more strongly to mercury(II) than to zinc(II), cadmium(II), silver(I) and lead(II). NMR experiments to characterise the peptide-mercury interaction implicate the thioether sulfur as the site of mercury binding and indicate 1:1 stoichiometry. The crystal structure of ferrocenoyl-S-methyl-l-cysteine methyl ester is also reported. The greater responsiveness of these systems to mercury(II) makes them interesting leads for the development of biologically inspired sensors for this toxic heavy metal.     

New antimony-capped iron(II) and cobalt(III) clathrochelate precursors of the polytopic hybrid cage complexes: Synthesis,X-ray structures and electrochemistry

Direct template macrocyclization of the three dimethylglyoxime molecules on the iron(II) ion and the capping of nonmacrocyclic K₃CoDm₃ tris-dimethylglyoximate with triethylantimony(V) derivatives led to the formation of triethylantimony-capped iron(II) and cobalt(III) clathrochelates. The complexes obtained have been characterized using elemental analysis, MALDI-TOF mass, IR, UV–Vis, ⁵⁷Fe Mössbauer and ¹H and ¹³C NMR spectroscopies, and X-ray crystallography. The influence of the nature of an encapsulated metal ion, the capping groups and the chelate fragments on a clathrochelate framework geometry is discussed. The cyclic voltammograms show oxidation and reduction waves assignable to Fe^2+/3+ and Co^2+/3+ couples of the encapsulated metal ion.     

Synthesis, structure and properties of the macrocyclic ferrocenophanes with cyclopentadienyl ligands tethered by oligo(ethylene glycol) chain

Cyclization reactions of Fe{C₅H₄OCH₂(CH₂OCH₂)_nCH₂OTs}₂ (n = 1, 2) with C₆H₄-1,2-(OH)₂, C₆H₄-1,3-(OH)₂, and Fe(C₅H₄OAc)₂ under basic conditions yield the corresponding macrocyclic 1,1′-ferrocenophanes. The ferrocenophane having a pyrido-crown ether structure was also synthesized. These ferrocenophanes were characterized by X-ray crystallography and NMR spectroscopy. Cyclic voltammograms of the ferrocenophanes exhibited reversible redox peaks assigned to the oxidation and reduction of the ferrocene unit. The macrocyclic pyrido-containing ferrocenophane forms pseudorotaxane with [NH₂{(CH₂)₉Me}₂]BARF (BARF = B{C₆H₃-3,5-(CF₃)₂}₄) in CDCl₃.     

A tetranuclear copper(II) complex: crystal structure,assembly, EPR,electrochemistry and magnetism

A tetranuclear copper(II) complex, [Cu₂L]₂(ClO₄)₂ · 4H₂O (1), where H₃L = N,N′-bis(4-(3′-formyl-5′-chlorosalicyclidene)iminoethyl)-4-chloro-2,6-bimethyliminophenol, has been synthesized and structurally characterized by ES-MS, IR and X-ray crystallography. The complex is a dimer of two dinuclear copper(II) acylic enantiomorph subunits ([Cu₂L]ClO₄ · 2H₂O), held together by π–π, coordination and hydrogen bond interactions. The Cu–Cu separation in each subunit, bridged by one phenoxide, is 3.228 Å, and the shortest distance of Cu–Cu between the two subunits is 3.252 Å. There are two crystallographically unique copper(II) environments, one (Cu1) is square-based pyramidal with O₃N₂ donor set, another (Cu2) square planar with O₂N₂ donor set. The cyclic voltammogram of the complex shows that it undergoes two stepwise reduction processes, E _pc = ?0.707 and ?0.850 V, respectively. Magnetic measurements in the 2–300 K range indicate strong antiferromagnetic interactions between Cu(II) ions in each subunit with the exchange constant J = ?211(2) cm^?1. The observation has been rationalized on the basis of the effective magnetic pathway.     

Tetrathiafulvalene-based lanthanide coordination complexes: Synthesis,crystal structure,optical and electrochemical characterization

The explorative lanthanide coordination chemistry of 4′,5′-bis-(propylthio)tetrathiafulvenyl[i]dipyrido[3,2-a:2′,3′-c]phenazine (TTF-dppz) is described. Thereby, four new Ln(III) complexes, [Ln(NO₃)₃(TTF-dppz)₂] with Ln(III) = Nd (1), Eu (2), Gd (3), Tb (4), have been prepared and characterized. An X-ray crystallographic study of [Gd(NO₃)₃(TTF-dppz)₂] (3) shows that the Gd(III) ion is coordinated to six oxygen atoms from three bidentate nitrate ligands and four nitrogen atoms from two bidentate TTF-dppz molecules forming a distorted bicapped square antiprism coordination geometry. The UV-vis spectra of the four Ln(III) complexes show very strong absorption bands in the UV region consistent with ligand centred electronic π-π* transitions and an intense broad absorption band in the visible region corresponding to a spin-allowed electronic π-π* ¹ILCT transition from the TTF-dppz ligand. Upon coordination, the ¹ILCT band of the free TTF-dppz ligand is bathochromically shifted. The electrochemical studies reveal that all complexes undergo two reversible oxidation and one (quasi)reversible reduction processes, ascribed to the successive oxidations of the TTF moiety and the reduction of the dppz unit, respectively. Moreover, the magnetic properties of complexes 3 and 4 are discussed.     

Crystal structure,bioactivities, and electrochemistry properties of four diverse complexes with a new pyrazole ligand

Four complexes, [Cu(cmpa)(Hpdbl)] ? 2H₂O (1), [Cd(cmpa)₂] ? 2.5H₂O (2), [Cu(cmpa)₂] ? 2.5H₂O (3), and [Pb(cmpa)₂] · 2.5H₂O (4), have been synthesized and characterized based on the pyrazole ligand (Hcmpa = 3-chloro-6-(3,5-dimethy-1-yl)picolinic acid, H₂pdbl = pyridine-2,6-dicarboxylic acid). Complexes 1–4 showed 3-D supramolecular architectures that are connected through hydrogen bonds and aromatic π–π interactions. Preliminary antibacterial activities of the complexes indicated selective inhibition for the tested strains. The electrochemistry of 1–4 was studied by cyclic voltammetry in DMSO using a glassy carbon working electrode.     

Ruthenium(II) complexes with ferrocene-modified arene ligands: synthesis and electrochemistry

A series of arene-ruthenium complexes of the general formula [RuCl₂{η⁶-C₆H₅(CH₂)₂R}L] with R=OH, CH₂OH, OC(O)Fc, CH₂OC(O)Fc (Fc=ferrocenyl) and L=PPh₃, (diphenylphosphino)ferrocene, or bridging 1,1^′-bis(diphenylphosphino)ferrocene, have been synthesized. Two synthetic pathways have been used for these ferrocene-modified arene-ruthenium complexes: (a) esterification of ferrocene carboxylic acid with 2-(cyclohexa-1,4-dienyl)ethanol, followed by condensation with RuCl₃ · nH₂O to afford [RuCl₂{η⁶-C₆H₅(CH₂)₂OC(O)Fc}]₂, and (b) esterification between ferrocene carboxylic acid and [RuCl₂{η⁶-C₆H₅(CH₂)₃OH}L] to give [RuCl₂{η⁶-C₆H₅(CH₂)₃OC(O)Fc}L]. All new compounds have been characterized by NMR and IR spectroscopy as well as by mass spectrometry. The single-crystal X-ray structure analysis of [RuCl₂{η⁶-C₆H₅(CH₂)₃OH}(PPh₃)] shows that the presence of a CH₂CH₂CH₂OH side-arm allows [RuCl₂{η⁶-C₆H₅(CH₂)₃OH}(PPh₃)] to form an intramolecular hydrogen bond with a chlorine atom. The electrochemical behavior of selected representative compounds has been studied. Complexes with ferrocenylated side arms display the expected cyclic voltammograms, two independent reversible one-electron waves of the Ru(II)/Ru(III) and Fe(II)/Fe(III) redox couples. Introduction of a ferrocenylphosphine onto the ruthenium is reflected by an additonal reversible, one-electron wave due to ferrocene/ferrocenium system which is, however, coupled with the Ru(II)/Ru(III) redox system.     

Molecular structure and electrochemical properties of the Pt complex of 1,1′-bis(methylthio)ferrocene and the Pd complexes of 1,4,7-trithia[7]- and 1,5,9-trithia[9] (1,1′)ferrocenophanes

Molecular structures of (triphenylphosphine) [1,1′-bis-(methylthio)ferrocene-S,S′,Fe]Pt(BF₄)₂ (1), (1,5,9-trithia[9]ferrocenophane-S,S′,S″,Fe)Pd(BF₄)₂ (2), and (acetonitrile)(1,4,7-trithia[7]ferrocenophane-S,S′,S″,Fe)Pd(BF₄)₂ (3) were determined by X-ray analyses. The Pt in 1 and the Pd atom in 2 have a somewhat distorted square-planar geometry including the Fe atom of the ferrocene moiety, while the Pd atom in 3 is coordinated by one equivalent of acetonitrile and takes a distorted tetragonal-pyramidal geometry. The distances of the Fe---M bond (M = Pd, Pt) in 1–3 are 2.851(2), 2.827(2), and 3.0962(8) Å, respectively. Cyclic voltammetry of 1–3 gave no reversible wave, but afforded some information supporting the presence of a dative bond.     

In situ studies: electrochemistry and scattering

Given the global relevance of sustainable energy and energy security, the study of electrochemistry and the development of energy storage devices is a very active area of research. As researchers attempt to overcome issues with current energy storage devices, innovative methods are required to probe deeper into the working mechanisms of devices. The ability to study electrochemistry as it takes place in electrochemical energy storage devices has been enabled by continuous developments in instrumentation, improved accessibility for researchers and also innovations in data collection and cell design. In this short review, we highlight several studies that make use of innovations in data collection, data interpretation, or device design, to study electrochemical energy storage devices using scattering methods.     

Synthesis,spectroscopic properties,structural characterization and electrochemistry of mixed ligand complexes of copper(I) halide with PPh3 and naphthylazoimidazole

The reaction of CuX (X = Cl, Br, I) with a mixture of PPh₃ and 1-alkyl-2-(naphthyl-α/β-azo)imidazole has synthesized mixed ligand complexes of the composition, [Cu(α/β-NaiR)(PPh₃)X]. The spectroscopic characterization (IR, UV–Vis, ¹H NMR) supports this formulation. The single crystal X-ray diffraction study of [Cu((α-NaiMe)(PPh₃)I] (7a) (α-NaiMe = 1-methyl-2-(naphthyl-α-azo)imidazole) shows a distorted tetrahedral geometry about Cu(I). Cyclic voltammograms of the complexes show a high potential Cu(II)/Cu(I) couple and azo reductions. The [Cu(α/β-NaiR)(PPh₃)I] complexes show an additional oxidative response at 0.4 V that is assigned to I/I⁻ A sharp anodic peak at ∼−0.2 V is assigned to the oxidation of metallic Cu, deposited on electrode surface upon scanning to the negative side of the SCE. DFT and TD-DFT computations of [Cu((α-NaiMe)(PPh₃)I] (7a), [Cu((α-NaiMe)(PPh₃)I]⁺ (7a⁺) and [Cu((α-NaiMe)(PPh₃)I]⁻ (7a⁻) were carried out to examine the electronic configuration and to explain the spectral and redox properties of the complexes.     

Mono and dinuclear iridium, rhodium and ruthenium complexes containing chelating carboxylato pyrazine ligands: Synthesis, molecular structure and electrochemistry

The mononuclear complexes [(η⁵-C₅Me₅)IrCl(L¹)] (1), [(η⁵-C₅Me₅)RhCl(L¹)] (2), [(η⁶-p-PrⁱC₆H₄Me)RuCl(L¹)] (3) and [(η⁶-C₆Me₆)RuCl(L¹)] (4) have been synthesised from pyrazine-2-carboxylic acid (HL¹) and the corresponding complexes [{(η⁵-C₅Me₅)IrCl₂}₂], [{(η⁵-C₅Me₅)RhCl₂}₂], [{(η⁶-p-PrⁱC₆H₄Me)RuCl₂}₂], and [{(η⁶-C₆Me₆)RuCl₂}₂], respectively. The related dinuclear complexes [{(η⁵-C₅Me₅)IrCl}₂(μ-L²)] (5), [{(η⁵-C₅Me₅)RhCl}₂(μ-L²)] (6), [{(η⁶-p-PrⁱC₆H₄Me)RuCl}₂(μ-L²)] (7) and [{(η⁶-C₆Me₆)RuCl}₂(μ-L²)] (8) have been obtained in a similar manner from pyrazine-2,5-dicarboxylic acid (H₂L²). Compounds isomeric to the latter series, [{(η⁵-C₅Me₅)IrCl}₂(μ-L³)] (9), [{(η⁵-C₅Me₅)RhCl}₂(μ-L³)] (10), [{(p-PrⁱC₆H₄Me)RuCl}₂(μ-L³)] (11) and [{(η⁶-C₆Me₆)RuCl}₂(μ-L³)] (12), have been prepared by using pyrazine-2,3-dicarboxylic acid (H₂L³) instead of H₂L². The molecular structures of 2 and 3, determined by X-ray diffraction analysis, show the pyrazine-2-carboxylato moiety to act as an N,O-chelating ligand, while the structure analyses of 5-7, confirm that the pyrazine-2,5-dicarboxylato unit bridges two metal centres. The electrochemical behaviour of selected representatives has been studied by voltammetric techniques.     

Synthesis, structure, photochromism and DFT calculations of copper(I)-triphenylphosphine halide complexes of thioalkylazoimidazoles

[Cu(SRaaiNR′)(PPh₃)X] complexes are synthesized by the reaction of CuX (X = Cl, Br, I), triphenylphosphine and 1-alkyl-2-[(o-thioalkyl)phenylazo]imidazole (SRaaiNR′). The single crystal X-ray structure of [Cu(SEtaaiNH)(PPh₃)I] (SEtaaiNH = 2-[(o-thioethyl)phenylazo]imidazole) shows a distorted tetrahedral geometry of the copper center with bidentate, N(azo), N(imidazole) chelation of SEtaaiNH and coordination from PPh₃ and iodine. These complexes show a trans-to-cis isomerization upon irradiation with UV light. The reverse transformation, cis-to-trans isomerization, is very slow with visible light irradiation and is thermally accessible. The quantum yields (?_t→c) of the trans-to-cis isomerization of [Cu(SRaaiNR′)(PPh₃)X] are lower than the free ligand values. This is due to the increased mass and rotor volume of the complexes compared to the free ligand data. The rate of isomerization follows the order: [Cu(SRaaiNR′)(PPh₃)Cl] < [Cu(SRaaiNR′)(PPh₃)Br] < [Cu(SRaaiNR′)(PPh₃)I]. The activation energy (E_a) of the cis-to-trans isomerization is calculated by a controlled temperature reaction. DFT computation of representative complexes has been used to determine the composition and energy of the molecular levels.