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.     

Synthesis and electrochemical and photophysical studies of tetrathiafulvalene-annulated phthalocyanines

The synthesis of tetrakis(tetrathiafulvalene)-annulated metal-free and metallophthalocyanines 5-8 via the tetramerization of the phthalonitrile derivative 4 is reported. All of them have been fully characterized by electronic absorption spectroscopy, thin-layer cyclic voltammetry, mass spectrometry, and elemental analysis. Their solution electrochemical data show two reversible four-electron oxidation waves, indicating that these fused systems are strong pi-electron donors, which give rise to tetra- or octaradical cation species. For the metal-free phthalocyanine 5, additionally a reversible one-electron wave was found in the negative direction arising from the reduction of the macrocycle. Moreover, the tetrathiafulvalene unit acts as an efficient reductive electron-transfer quencher for the phthalocyanine emission, but upon its oxidation, an intense luminescence is switched on.     

Synthesis,characterization and electrochemical properties of new phthalocyanines

The chemical synthesis and characterization with spectroscopic and electrochemical properties of [bis(4-fluorophenyl)-methoxy]-substituted metallo-phthalocyanines were reported for the first time. The new phthalocyanines have been characterized by elemental analysis, UV-Vis, FT-IR, and mass spectroscopies. The aggregation behavior of the phthalocyanine compounds was investigated in different solvents and concentrations. It is found that the fluoro substituents of peripherally Co and Cu complexes are examined and induce a shift to the redox processes toward the negative potentials and formed more reversible processes. Metal-based reduction and oxidation reactions were obtained for the Co(II) complex, whereas Cu(II) complexes exhibited Pc-ring-based electron-transfer reactions. The voltammetric measurements supported the proposed structure of the complexes.     

Anionic water-soluble sulfonated phthalocyanines: microwave-assisted synthesis,aggregation behaviours,electrochemical and in-situ spectroelectrochemical characterisation

In this work, a phthalonitrile derivative bearing p-sulfonylphenoxy group at the 3-position has been synthesised. The water-soluble non-peripherally tetrasubstituted zinc (3) and cobalt (4) phthalocyanines were obtained by cyclotetramerisation of this phthalonitrile derivative in the presence of anhydrous metal salts by microwave irradiation. The compounds have been characterised by using FT-IR, ¹H NMR, UV–Vis and Mass spectrometry (MS) data. The aggregation behaviours of these compounds were investigated in methanol, DMSO, DMF, and water. We have also studied the aggregation behaviours of the phthalocyanine complex 3 in various DMSO/water mixtures. Additionally, the redox properties of the phthalocyanine complexes were examined in dimethylsulfoxide by voltammetry and in situ spectroelectrochemistry. Redox behaviours of the complexes supported the structures of the complexes. Metal and ring-based reductions were observed for 4 and only ring-based electron transfer processes were observed with 3.     

Synthesis and electrochemical properties of phthalocyanines with four 8-quinolinoxy-substituents

A metal-free phthalocyanine and its cobalt(II) and copper(II) phthalocyanate complexes were prepared by cyclotetramerization of 4-(8-quinolinoxy)phthalonitrile. The new compounds were characterized by elemental analyses, ¹H-n.m.r., i.r. and u.v.–vis. spectral data. Electrochemical measurements indicated that CoPc had two metal based and two ligand based redox couples, while H₂Pc and CuPc showed four ligand based redox couples. For all complexes, linear variation of the peak current of the first reduction peak (I _pc) with scan rate () indicated the adsorption of the complexes to the electrode surface.     

The synthesis and characterization of new phthalocyanines containing hexaazadithia macrobicyclic moieties

The new metal-free and metallo phthalocyanines (4) and (5) bearing four tetrasubstituted hexaazadithia macrobicycles on peripheral positions, have been synthesized. Phthalonitrile (3) has been synthesized from the reaction of (1,3,6,9,11,14 hexaazatricyclo [12.2.1.1^6,9]) (1) and 1,2-bis(2-iodomercaptoethyl)-4,5-dicyanobenzene (2). The new compounds were characterized by elemental analysis, and IR, ¹H, ¹³C-NMR, UV-Visible and mass spectral data.     

Synthesis,spectroscopy and electrochemical properties of highly soluble fluoro containing phthalocyanines

2(3),9(10),16(17),23(24)-Tetrakis-4′-[3,5-bis-(trifluoromethyl)-phenoxy]-phthalocyanines, {M[Pc-β(OBz-(CF₃)₂)₄]}, (M = Zn(II), Cu(II), Co(II) and Ni(II)) were synthesized and characterized by elemental analysis, FTIR, ¹H NMR, UV–Vis and MS (Maldi-TOF) spectral data. It is shown that the 4-(3,5-bis(trifluoromethyl)-phenoxy) moieties on the periphery affect the solubility, spectroscopic data and electrochemistry of the tetrakis metallophthalocyanines. The cyclic voltammetry and differential pulsed voltammetry of the complexes give well-defined redox couples in harmony with common metallophthalocyanine complexes. Electrochemical studies show that the complexes exhibit stable monoanionic M{Pc-β-[(OBz-(CF₃)₂)₄]}¹⁻, dianionic M{Pc-β-[(OBz-(CF₃)₂)₄]}²⁻ and monocationic M{Pc-β-[(OBz-(CF₃)₂)₄]}¹⁺ species during the reduction and oxidation processes. When compared with the unsubstituted analogues, the redox potentials of the complexes shifted to more positive potentials due to the electron-withdrawing fluorine groups.     

The electrochemical behaviour of bronze in synthetic seawater

This paper reports a voltammetric study of bronze in synthetic seawater (SSW). The effects of buffering and deoxygenating were particularly visible in the transpassive region. The breakdown of the anodic passive film on bronze leads to a well-defined activation peak in the transpassive region typical of a nucleation and growth of pits. The breakdown potential of the passivity was shown to vary with the experimental conditions, namely, with buffering and deoxygenating. Buffering has shown to lead to more stable passive films and deoxygenating to higher oxidation currents. Scanning electron microscopy with energy dispersive spectrometer (SEM/EDS) studies of bronze samples with 1-month exposure in non-deoxygenated buffered and non-buffered SSW under open circuit potential have shown significant differences in their morphology: a uniformly cracked surface and a surface showing large and spherical precipitates of about 50 μm uniformly distributed along the surface, respectively, for bronze coupons in buffered (pH 9) and in non-buffered SSW. The EDS technique has identified Cu, O, Cl and Na on the corrosion products of bronze in non-buffered SSW, whilst in buffered media, Sn was also identified. In non-buffered media, open circuit potentials have shown to be all the time less negative than in the buffered media. After 1-month exposure the E _OCP of bronze samples in both media seem to converge to −0.131 and −0.155 V vs Ag|AgCl, respectively. This potential can be assigned to the formation of cuprite, Cu₂O and nantokite, CuCl. The analysis of the SEM images after the removal of the corrosion products has shown descuprification with higher intensity on the surface from coupons in non-buffered SSW.     

Catalysis of the electrochemical reduction of molecular dioxygen by metal phthalocyanines

Quantum theories of elementary heterogeneous electron transfer (ET) reactions in polar media have recently been extended to reactions which proceed through active intermediate electronic surface states or bands. On the basis of this theoretical framework — which is equivalent to inelastic tunnelling processes with strong phonon coupling — experimental data for the electrochemical reduction of molecular oxygen on various carbon-supported metal phthalocyanines have been analyzed. The data are compatible with a mechanism in which at first ET from catalyst to oxygen occurs followed by ET from carbon to catalyst. Furthermore, excitation of high-frequency intramolecular modes is important.     

Microwave-assisted synthesis and reverse saturable absorption of phthalocyanines and porphyrins

Soluble phthalocyanines, including tetrakis(2,9,16,23-cumylphenoxy) copper phthalocyanines (CuPc(β-CP)₄), tetrakis(1,8,15,22-cumylphenoxy) copper phthalocyanines (CuPc(α-CP)₄) as well as tetrakis(2,9,16,23-tert-butyl) copper phthalocyanines (CuPc(β-t-butyl)₄), and porphyrins (5,10,15,20-tetrakis(4-tert-butylphenyl)porphyrins; M(TBP), M=H₂, Zn, Cu, Mg, InCl, AlCl) have been quickly synthesized by microwave irradiation. Furthermore, their reverse saturable absorption have also been investigated by dissolving them in solvent or incorporating them in polymer-silica hybrid material with a sol-gel process with polyvinyl butyral and tetraethyl orthosilicate as precursors. A new method for the preparation process of phthalocyanines and porphyrins in the solids has been successfully used.     

Efficient synthesis of brominated tetrathiafulvalene (TTF) derivatives: solid-state structure and electrochemical behaviour

An efficient synthesis is reported for 4,5-dibromo-[1,3]dithiole-2-thione (1) and 4-bromo-1,3-dithiole-2-thione (7) by bromination of lithiated vinylene trithiocarbonate. Compound 1 acts as a convenient precursor to a number of asymmetric electron donors. This is exemplified by the formation of 4,5-dibromo-4′,5′-bis(2′-cyanoethylsulfanyl)TTF (3) by cross-coupling methodology and subsequent conversion into 4,5-dibromo-4′,5′-ethylenedithioTTF (4) by reaction with caesium hydroxide and 1,2-dibromoethane. The new donor 4,5-dibromo-4′,5′-ethylenedithiodiselenadithiafulvalene (5) was prepared by cross-coupling of 1 and 4,5-ethylenedithio-1,3-diselenol-2-one (6). The X-ray structures of 3 and 5 are reported.     

Synthesis and electrochemical properties of crown ether functionalized coumarin substituted cobalt and copper phthalocyanines

The synthesis of novel 6,7-[15-crown-5]-3-[p-(3,4-dicyanophenoxy)phenyl]coumarin (1)/6,7-[15-crown-5]-3-[p-(2,3-dicyanophenoxy)phenyl]coumarin (2) and their peripherally/non-peripherally cobalt and copper phthalocyanine complexes (3-6) have been prepared and characterized by elementel analysis, ¹H-NMR, MALDI-TOF, FT-IR and UV-Vis spectral data. Fluorescence intensity changes of compound 1 and 2 have been determined by addition of Na⁺ or K⁺ ions at 25 °C in THF. The effect of substitution type on the redox and aggregation behaviour of the compounds was investigated by voltammetry and in situ spectroelectrochemistry.     

A new synthesis and the electrochemical behaviour of nickel(II) dithiophosphate and dithiophosphinate complexes

Summary The [Ni(S₂PR₂)₂] complexes (R=i-PrO, PhO, or Et) can be conveniently prepared by reaction of [Ni{P(OPh)₃}₄] with [R₂P(S)S]₂ (R=i-PrO, PhO, or Et) in refluxing CHCl₃. The electrochemical behaviour of the complexes in CH₂Cl₂ and MeCN has been studied by cyclic voltammetry and coulometry. The oxidation of complexes at a glassy carbon reveals an e.c. mechanism. The [Ni(S₂PR₂)₂] complexes undergo a one-electron irreversible reduction.     

Direct electrochemical synthesis of metal complexes of phthalocyanines and azomethines as model compounds: advantages and problems of this method versus traditional synthetic techniques

A comparison of traditional and electrochemical synthetic techniques for obtaining metal complexes of azomethine and phthalocyanine is reported. It is shown that the electrochemical method affords azomethinic coordination compounds free of anions of precursors and with higher yields at ambient temperature. Electrolysis in a solid phase of phthalonitrile using a high-surface platinum cathode leads to metal-free phthalocyanine and metal phthalocyaninates at 0–25°C. The typical problems of the electrosynthetic procedures in different conditions are discussed in detail.     

The electrochemical behaviour of the altenuene mycotoxin and its acidic properties

The electrooxidation of altenuene (ALT), one of the mycotoxins of the Alternaria alternata genus, on a glassy carbon disk electrode is studied for the first time by using cyclic and square wave voltammetry. From the electrochemical responses, a complex reaction mechanism could be inferred. Values of 1.06×10⁻⁵ cm² s⁻¹, 1.116 V and 2 were determined for the diffusion coefficient, the apparent formal potential and the electron number, respectively, for the overall electrode process by convolution analysis of linear scan voltammograms. Square wave voltammetry was used to generate I_p versus c_ALT* calibration curves for this fungal metabolite. A detection limit of 4.0×10⁻⁷ M was determined for a 2:1 signal to noise ratio. The acid dissociation constant for ALT was determined from conventional UV–vis spectrophotometric measurements. Experimental variations of absorbance as a function of pH at a given wavelength were fitted by using the exact equation that describes the system. Good agreement between the experimental absorbance versus pH plots and the curves generated by the fitting process was found.     

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.