Electron-rich tetrathiafulvalene-triarylamine conjugates: synthesis and redox properties

By combining tetrathiafulvalenes (TTFs) and triarylamines, four TTF-triarylamine conjugates bridged by an annulated pyrrole ring were designed and synthesized by an N-arylation reaction. Electrochemical and photophysical investigations suggest that these novel conjugates possess very strong electron-donating ability with very high HOMO energy levels of around -4.70 eV; the HOMOs are mainly located on the TTF moiety. We observed significant electronic coupling between the TTF moieties and the triarylamine groups. However, no evidence for such electronic communication between end-capping TTF units (conjugates 5 and 7) or between two terminal triarylamine groups (conjugate 9) could be found. Differential scanning calorimetry (DSC) measurements together with PM3-optimized geometries suggest that conjugates 5 and 7, which adopt three-dimensional propeller-shaped structures, may easily pack and crystallize in the solid state because of the large rigid planar blades consisting of TTF and one of the phenyl rings of the triarylamine moiety. However, conjugate 9, with two bulky end-capping triarylamine groups, forms an amorphous material with a glass transition at 74.5 degrees C.     

Co(II) and Fe(II) phthalocyanines: synthesis,investigation of their catalytic activity towards phenolic compounds and electrochemical behaviour

4‐[(1‐Benzylpiperidin‐4‐yl)oxy]‐substituted cobalt(II) and iron(II) phthalocyanine complexes were synthesized and their catalytic activity towards various phenolic compounds was investigated. Converting from environmentally harmful phenolic compounds into less harmful oxidation products using phthalocyanines makes this study attractive. This catalysis is feasible and time‐saving in terms of procedure and the best oxidation conditions determined. Electrochemical studies were also carried out using cyclic voltammetry and square wave voltammetry techniques. Voltammetric analyses of the synthesized phthalocyanine complexes supported their proposed structures. Copyright © 2015 John Wiley & Sons, Ltd.     

Two-step electrochemically directed synthesis of Pr4N(TCNQ)n (n=1, 2): preparation, structure, and properties of a magnetically isolated dimer and a quasi-one-dimensional chain

Solid-state electrochemistry of a tetracyanoquinodimethane (TCNQ)-modified electrode in contact with a tetrapropylammonium cation (Pr(4)N(+)) electrolyte showed two electron-transfer steps to give Pr(4)N(TCNQ)(2) (1) and Pr(4)N(TCNQ) (2) rather than the traditional one-electron step to directly give Pr(4)N(TCNQ). Two thermodynamically stable Pr(4)N(+)-TCNQ stoichiometries, 1 and 2, were synthesized and characterized. The degree of charge transfer (ρ) calculated from the crystal structure is -0.5 for the TCNQ moieties in 1 and -1.0 for those in 2. Raman spectra for Pr(4)N(TCNQ)(2) show only one resonance for the extracyclic C=C stretching at 1423 cm(-1), which lies approximately midway between that of TCNQ at 1454 cm(-1) and TCNQ(-) at 1380 cm(-1). Both the magnetic susceptibility and EPR spectra are temperature-dependent, with a magnetic moment close to that for one unpaired electron per (TCNQ)(2) unit in 1, whereas 2 is almost diamagnetic. Pressed discs of both complexes show conductivity (1-2×10(-5) S cm(-1)) in the semiconductor range. For 1, the position of zero current for the steady-state voltammograms implies 50% of TCNQ(-) and 50% TCNQ(0) is present in solution, thereby supporting a dissociation of (TCNQ)(2)(-) in solution, but is indicative of only TCNQ(-) being present for 2.     

Synthesis and electropolymerization studies of non-aggregated (4-{3-[3-(dimethylamino,diethylamino)phenoxy]propoxy}phenyl)propanoxy substituted silicon naphthalocyanines

In this study, 3-(4-{3-[3-(dimethylamino)phenoxy]propoxy}phenyl)propan-1-ol, 3-(4-{3-[3-(diethylamino)phenoxy]propoxy}phenyl)propan-1-ol and axially disubstituted silicon naphthalocyanines (SiNc) bearing electropolymerizable bis-[(4-{3-[3-(dimethylamino)phenoxy]propoxy}phenyl)propanoxy] and bis-[(4-{3-[3-(diethylamino)phenoxy]propoxy}phenyl)propanoxy] units were synthesized for the first time. Aggregation behavior of SiNcs was examined in different solvents and concentrations in DMSO. In all solvents and concentrations, SiNcs were non-aggregated. Also, electrochemical studies of SiNcs were investigated by cyclic and square wave voltammetry. While SiNcs gave only naphthalocyanine-based reduction process during the cathodic potential scans, they were electropolymerized on the working electrode during the anodic potential scan because of the oxidative electropolymerization of (4-{3-[3-(dimethylamino)phenoxy]propoxy}phenyl)propanoxy and (4-{3-[3-(diethylamino)phenoxy]propoxy}phenyl)propanoxy groups on the substituents of the complexes.     

Capacitance Effects Superimposed on Redox Processes in Molecular‐Cluster Batteries: A Synergic Route to High‐Capacity Energy Storage

Rechargeable molecular‐cluster batteries (MCBs) based on the manganese cluster complex [Mn₁₂O₁₂(CH₃CH₂C(CH₃)₂COO)₁₆(H₂O)₄] ([Mn12]) that exhibited a capacity of approximately 200 A h kg^?1 in the battery voltage range of 4.0 to 2.0 V were developed. In these batteries, the capacity of approximately 100 A h kg^?1 in the range of 4.0–3.0 V is caused by a chemical reduction from [Mn12]⁰ to [Mn12]^8?, whereas the other half in the range of 3.0–2.0 V cannot be explained by a redox change of the Mn ions. We performed the cyclic voltammetry (CV) and ⁷Li solid‐state NMR measurements on the Mn12‐MCBs to investigate the origin of the capacity below 3.0 V. Pseudo‐rectangular‐shaped CV curves in the range of 3.0–2.0 V demonstrate the presence of an electrical double‐layer (EDL) capacitance in Mn12‐MCBs, which corresponds to approximately 100 A h kg^?1. ⁷Li NMR studies suggest that Li ions form an EDL with electrons in carbon black electrodes in the capacitance voltage range. The capacitance effects are not formed by the single‐carbon electrodes alone, but appear only in the mixture of Mn12 and the carbon black electrodes. This type of coexistence of capacitance effects and redox reaction in one electrochemical cell is quite unusual and can serve as a new working principle for high‐performance energy‐storage devices.     

Synthesis,characterization and electrochemical properties of amphiphilic axially-disubstituted silicon(IV) phthalocyanines

The new 2-[2-(6-tert-butyl-2H-1,3-benzoxazin-3(4H)-yl)ethoxy]ethanol 1 and 2-[2-(6-pentyl-2H-1,3-benzoxazin-3(4H)-yl)ethoxy]ethanol 2 have been synthesized. Axially disubstituted silicon phthalocyanines 3 and 4 have been synthesized by introducing 2-[2-(6-tert-butyl-2H-1,3-benzoxazin-3(4H)-yl)ethoxy]ethanol and 2-[2-(6-pentyl-2H-1,3-benzoxazin-3(4H)-yl)ethoxy]ethanol at the axial positions of silicon(IV) phthalocyanine, respectively. The electrochemical properties of silicon phthalocyanines 3 and 4 were also investigated by cyclic voltammetry (CV) and square wave voltammetry. Voltammetric studies show that while 3 showed two reversible reduction and one irreversible oxidation couples, 4 showed two quasi-reversible reduction and one irreversible oxidation couples.     

New homoleptic organometallic derivatives of vanadium(III) and vanadium(IV): synthesis, characterization, and study of their electrochemical behaviour

The arylation of [VCl3(thf)3] with LiR(Cl), where R(Cl) is a polychlorinated phenyl group [C6Cl5, 2,4,6-trichlorophenyl(tcp), or 2,6-dichlorophenyl (dcp)] gives four-coordinate, homoleptic organovanadium(III) derivatives with the formula [Li(thf)(4)][V(III)(R(Cl))(4)] (R(Cl) = C(6)Cl(5) (1), tcp (2), dcp (3)). The anion [V(III)(C6Cl5)4]- has an almost tetrahedral geometry, as observed in the solid-state structure of [NBu4][V(C6Cl5)4] (1') (X-ray diffraction). Compounds 1-3 are electrochemically related to the neutral organovanadium(IV) species [V(IV)(R(Cl))4] (R(Cl) = C6Cl5 (4), tcp (5), dcp (6)). The redox potentials of the V(IV)/V(III) semisystems in CH2Cl2 decrease with decreasing chlorination of the phenyl ring (E(1/2) = 0.84 (4/1), 0.42 (5/2), 0.25 V (6/3)). All the [V(IV)(R(Cl))4] derivatives involved in these redox couples could also be prepared and isolated by chemical methods. The arylation of [VCl(3)(thf)(3)] with LiC6F5 also gives a homoleptic organovanadium(III) compound, but with a different stoichiometry: [NBu4]2[V(III)(C6F5)5] (7). In this five-coordinate species, the C6F5 groups define a trigonal bipyramidal environment for the vanadium atom (X-ray diffraction). EPR spectra for the new organovanadium compounds 1-6 are also given and analysed in terms of an elongated tetrahedral structure with C(2v) local symmetry. It is suggested that the R(Cl) groups exert a protective effect towards the vanadium centre.     

Anodic synthesis and properties of polyaminothiazole

The possibility of electrooxidative polymerization of 2-aminothiazole in aqueous and organic media is studied using the cyclic voltammetry method. Anodic synthesis conditions are found that provide the polyaminothiazole conducting film synthesis on platinum and tin dioxide electrodes. IR and electron spectroscopy studies show that the polymer synthesized on the electrode surface contains fragments of π-conjugated bonds that provide optical absorption in the visible region and electrochemical activity of the film. A scheme is suggested for the reactions of oxidative coupling of 2-aminothiazole.     

Bis‐Coenzyme Q0: Synthesis,Characteristics, and Application

A methylene‐bridged bis‐coenzyme Q₀, bis(2,3‐dimethoxy‐5‐methyl‐l,4‐benzoquinone)methane (Bis‐CoQ₀), that shows intramolecular electronic communications has been synthesized for the first time. By employing electrochemical, in situ UV/Vis, and electron paramagnetic resonance (EPR) spectroelectrochemical techniques, the unstable reduced intermediate species—monoradicals, diamagnetic dianions and tetraanions of Bis‐CoQ₀—have been observed. The electron‐transfer process can be defined as a three‐step reduction process with a total of four electrons in solution in CH₃CN. The chemical reaction in the third redox step process was confirmed by variable temperature cyclic voltammetry. In an aprotic CH₃CN solution, the peak potential separation between electron‐transfer steps diminished sequentially with increasing concentration of water. The hydrogen‐bonding interactions between water and the electrochemically reduced intermediates of Bis‐CoQ₀ can be estimated by peak potential shifts. The electronic communications of Bis‐CoQ₀ may have been blocked when one reduction peak was observed with proper quantities of water in CH₃CN solution. The antioxidant defense capacity of Bis‐CoQ₀‐protected cells has also been assessed.     

Highly conjugated p-quinonoid pi-extended tetrathiafulvalene derivatives: a class of highly distorted electron donors

A new class of pi-extended TTF-type electron donors (11 a-c) has been synthesized by Wittig-Horner olefination of bianthrone (9) with 1,3-dithiole phosphonate esters (10 a-c). In cyclic voltammetry experiments, donors 11 a-c reveal a single, electrochemically irreversible oxidation-yielding the corresponding dicationic products-at relatively low oxidation potentials (approximately 0.7-0.8 V). Theoretical calculations, performed at the DFT level (B3 P86/6-31 G*), predict a highly-folded C(2h) structure for 11 a. In the ground state, the molecule adopts a double saddle-like conformation to compensate the steric hindrance. The calculations suggest that the intramolecular charge transfer associated with the HOMO-->LUMO transition is responsible for an absorption band observed above 400 nm. While the radical cation 11 a*+ retains the folded C(2h) structure predicted for the neutral molecule as the most stable conformation, the dication 11 a(2+) has a fully aromatic D(2) structure, formed by an orthogonal 9,9'-bianthryl central unit to which two singly-charged dithiole rings are attached. The drastic conformational changes that compounds 11 undergo upon oxidation account for their electrochemical properties. By means of pulse radiolysis measurements, radical-induced one-electron oxidation of 11 a-c was shown to lead to the radical cation species (11 a-c*+), which were found to disproportionate with generation of the respective dication species (11 a-c(2+)) and the neutral molecules (11 a-c).     

A kinetically stabilized ferrocenyl diphosphene: synthesis, structure, properties, and redox behavior

A new, stable ferrocenyl diphosphene [Tbt-P==P-Fc] (1) (Tbt=2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Fc = ferrocenyl) was synthesized by the dehydrochlorination reaction of the corresponding diphosphane, [Tbt-P(H)-P(Cl)-Fc] (8), with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in good yield. Diphosphene 1 is very stable in the solid state and also in solution. In the 31P NMR spectrum (C6D6), diphosphene 1 showed a low-fielded AB quartet at delta 501.7 and 479.5 ppm with the coupling constant 1J(PP)=546 Hz, which is characteristic of an unsymmetrically substituted trans-diphosphene. The molecular structure of 1 was established by X-ray crystallographic analysis, which showed a trans-diphosphene with a C-P-P-C torsion angle of 177.86(17) degrees . The phosphorus-phosphorus bond length of 1 [2.0285(15) A] which is considerably shorter than the typical P-P single-bond lengths (ca. 2.22-2.24 A) and within the range of reported P=P double-bond lengths (1.985-2.051 A) for diaryl diphosphenes, evidenced the P=P double-bond character of 1 in the solid state. In addition, the cyclic voltammograms of 1 showed reversible reduction and oxidation couples at -1.95 and +0.34 V versus SCE, respectively. The electrochemical results for 1 were reasonably supported by the DFT calculations, which suggested that the LUMO and HOMO orbitals should be mainly pi* orbital of the diphosphene moiety and d orbitals of the iron(II) atom, respectively.     

Covalent tethering of organic functionality to the surface of glassy carbon electrodes by using electrochemical and solid-phase synthesis methodologies

Organic linkers such as (N-Boc-aminomethyl)phenyl (BocNHCH2C6H4) and N-Boc-ethylenediamine (Boc-EDA) have been covalently tethered onto a glassy carbon surface by employing electrochemical reduction of BocNHCH2C6H4 diazonium salt or oxidation of Boc-EDA. After removal of the Boc group, anthraquinone as a redox model was attached to the linker by a solid-phase coupling reaction. Grafting of anthraquinone to electrodes bearing a second spacer such as 4-(N-Boc-aminomethyl)benzoic acid or N-Boc-beta-alanine was also performed by following this methodology. The surface coverage, stability and electron transfer to/from the tethered anthraquinone redox group through the linkers were investigated by cyclic voltammetry. The effects of pH and scan rate were studied, and the electron-transfer coefficient and rate constant were determined by using Laviron's equation for the different types of linker. The combination of electrochemical attachment of protected linkers and subsequent modifications under the conditions of solid-phase synthesis provides a very versatile methodology for tailoring a wide range of organic functional arrangements on a glassy carbon surface.     

Synthesis of a new colorimetric receptor based on calix[4]pyrrole binding oxime for selective recognition of fluoride ions

A colorimetric anion sensor α-meso-heptaethylcalix[4]pyrrole-meso-3-aminophenyl-p-nitrobenzaldoxime was synthesised and characterised by various spectroscopic techniques. Anion-binding studies were carried out using UV–vis, and ¹H NMR titrations, revealing that the receptor exhibits selective recognition towards F^?  over other anions. The selectivity for F^?  among the halides is attributed mainly to the hydrogen bond interaction of the receptor with F^? . Receptor showed colour change from colourless to yellow in the presence of tetrabutylammonium fluoride with 1:2 stoichiometry. Cyclic voltammetry studies, carried out in CH₃CN, provided evidence of an anion-dependent electrochemical response with F^?  ion. This response was particularly dramatic in the case of receptor after the addition of ～1 equiv. of F^?  ion.     

The ball-shaped heteropolytungstates [[Sn(CH3)2(H2O)]24[Sn(CH3)2]12(A-XW9O34)12]36- (X=P, As): stability, redox and electrocatalytic properties in aqueous media

The electrochemical behavior of the ball-shaped heteropolytungstates [[Sn(CH(3))(2)(H(2)O)](24)[Sn(CH(3))(2)](12)(A-XW(9)O(34))(12)](36-) (X=P, 1; As, 2) was examined in aqueous electrolytes by redissolution of their respective mixed cesium-sodium salts Cs(14)Na(22)[[Sn(CH(3))(2)(H(2)O)](24)[Sn(CH(3))(2)](12) (A-PW(9)O(34))(12)]149 H(2)O (Cs(14)-1) and Cs(14)Na(22)[[Sn(CH(3))(2)(H(2)O)](24)[Sn(CH(3))(2)](12)(A-AsW(9)O(34))(12)]149 H(2)O (Cs(14)-2). In the studied media, Cs(14)-2 is readily soluble in contrast to the significantly less soluble Cs(14)-1. The solubility of Cs(14)-1 is increased by the presence of Li(+) ions in solution. Gel filtration studies with 1 and 2 rule out a decay of the dodecameric spherical assemblies to Keggin-based monomers on the timescale of the experiment. By UV/Vis spectroscopy and cyclic voltammetry, 2 was found to be significantly less stable than 1 and both polyanions also show rather different decomposition pathways. Polyanion 1 collapses first into Keggin-type monomers which might contain the trilacunary [A-alpha-PW(9)O(34)](9-). The final monomeric species obtained from 1 appears to be very similar to [PW(11)O(39)](7-), which is the final transformation product of [A-alpha-PW(9)O(34)](9-) in the same media. In contrast, 2 does not seem to follow an analogous transformation pathway as that of the trilacunary [A-alpha-AsW(9)O(34)](9-). Importantly, stabilization of 1 is observed in chloride media. The fairly long-term stability of 1 in 1 M LiCl, pH 3, has allowed for its electrochemical study to be carried out. The solid-state cyclic voltammogram of 1 entrapped in a carbon paste electrode shows the same characteristics as 1 dissolved in chloride solutions, thus supporting the conclusion that the polyanion is stable in these environments. Controlled potential coulometry on 1 indicates that the number of electrons consumed in the first wave is larger than twenty. To our knowledge, 1 constitutes the first example of a molecule that can take up such a large number of electrons resulting in a chemically reversible W-wave. These properties show promise for future fundamental and applied studies. Polyanion 1 is also efficient in the electrocatalytic reduction of NO(x), including nitrate. Finally, a remarkable interaction was found between 1 and NO, a highly promising feature for biomimetic applications.