Electrochemical behaviour of tetraazamacrocyclic nickel(II) complexes functionalized with crown ethers

Tetraazamacrocyclic nickel(II) complexes linked by the system of conjugated double bonds with one or two benzo-15-crown-5 moieties (2Ni and 3Ni) were synthesized and characterized. The CV of these complexes in acetonitrile (ACN) solution exhibited reversible Ni^II/III redox process. At more positive potentials oxidation of the bezno-15-crown-5 ether (B15C5) moiety was found. In complexes 2Ni and 3Ni redox potential of Ni^II/III did not change after the interactions of alkali and alkaline earth metal cations with B15C5 unit. However, the presence of guest cations caused a significant change of B15C5 oxidation potential. Complexation of two Cl⁻ anions to the coordinated Ni^II in 2Ni and 3Ni resulted in an appreciable shift of both Ni^II/III and B15C5 redox processes after addition of metal cations. Behaviour of complexes 2Ni and 3Ni was compared with behaviour of similar Cu^II complexes.     

Electrochemical characterisation of tetra- and octa-substituted oxo(phthalocyaninato)titanium(IV) complexes

The synthesis and electrochemical characterisation of the following oxotitanium tetra-substituted phthalocyanines are reported: 1,(4)-(tetrabenzyloxyphthalocyaninato)titanium(IV) oxide (5a); 1,(4)-{tetrakis[4-(benzyloxy)phenoxy]phthalocyaninato}titanium(IV) oxide (5b); 2,(3)-(tetrabenzyloxyphthalocyaninato)titanium(IV) oxide (6a) and 2,(3)-{tetrakis[4-(benzyloxy)phenoxy]phthalocyaninato}titanium(IV) oxide (6b). The electrochemical characterisation of complexes octa-substituted with 4-(benzyloxy)phenoxy (9b), phenoxy (9c) and tert-butylphenoxy (9d) groups is also reported. The cyclic voltammograms of the complexes exhibit reversible couples I-III and couple IV is quasi-reversible for complexes 5a, 5b, 6a and 6b. The first two reductions are metal-based processes, confirmed by spectroelectrochemistry to be due to Ti^IVPc²⁻/Ti^IIIPc²⁻ and Ti^IIIPc²⁻/Ti^IIPc²⁻ redox processes and the last two reductions are ring-based processes due to Ti^IIPc²⁻/Ti^IIPc³⁻ and Ti^IIPc³⁻/Ti^IIPc⁴⁻. Chronocoulometry confirmed a one-electron transfer at each reduction step. The electrochemistry of the above complexes is also compared to the previously reported 5c, 5d, 6c and 6d.     

Synthesis and electrochemical characterisation of benzylmercapto and dodecylmercapto tetra substituted cobalt, iron, and zinc phthalocyanines complexes

The work reports on cyclic voltammetry (CV), square wave voltammetry and spectroelectrochemistry of the following complexes: tetrakis (benzylmercapto) phthalocyanine complexes of Zn(II) (ZnTBMPc, 4a), Co(II) (CoTBMPc, 5a), and Fe(II) (FeTBMPc 6a); tetrakis (dodecylmercapto) phthalocyanine complexes of Zn(II) (ZnTDMPc, 4b), Co(II) (CoTDMPc, 5b), and Fe(II) (FeTDMPc, 6b). More reversible CV couples were observed for complexes 4a, 5a, and 6a containing thiol phenyl ring substituents. Complexes 4b, 5b, and 6b containing long chain thiol substituents showed less reversible couples. Complexes 6a and 6b showed a relatively large number of redox processes (5 for 6a and 6 for 6b) within the potential window employed in this work. The processes for FePc derivatives (6a) are assigned to Fe^IIIPc⁻¹/Fe^IIIPc⁻², Fe^IIIPc⁻²/Fe^IIPc⁻², Fe^IIPc⁻²/Fe^IPc⁻², Fe^IPc⁻²/Fe^IPc⁻³, and Fe^IPc⁻³/Fe^IPc⁻⁴ and for the CoPc derivative (5a) to Co^IIIPc⁻¹/Co^IIIPc⁻², Co^IIIPc⁻²/Co^IIPc⁻², Co^IIPc⁻²/Co^IPc⁻², and Co^IPc⁻²/Co^IPc⁻³.     

Highly active and trans-1,4 specific polymerization of 1,3-butadiene catalyzed by 2-pyrazolyl substituted 1,10-phenanthroline ligated iron (II) complexes

A new family of iron (II) complexes (2a–h) bearing tridentate 2-pyrazolyl substituted 1,10-phenanthroline ligands were successfully prepared and characterized by IR spectroscopy, elemental analysis, and mass spectra. Complexes 2a–f and 2h were further confirmed by the X-ray crystallographic analysis. 2a, 2b, 2e, and 2f adopted distorted trigonal bipyramidal configuration. 2c displayed a distorted octahedron formed by six coordinated nitrogen atoms of the two ligands. Linked by two bridged chloride atoms, complex 2d was a centrosymmetric dimmer, and complex 2h adopted a six-coordinate distorted octahedral geometry due to the coordination of two solvent molecules. These complexes activated by alkylaluminum were examined in butadiene polymerization. In combination with AlⁱBu₃, complexes 2a–c exhibited high catalytic activity (73.5%–94.3%) at 20 °C, whereas other complexes exhibited much lower activity. Interestingly, the activity and selectivity of the complexes increased as increasing polymerization temperature. In particular, 2b and 2c displayed both high activity (99% and 80%, respectively) and trans-1,4 selectivity (95.6% and 96.2%, respectively) at 60 °C. The trans-1,4 selectivity of 2b varied as alkylaluminum used as a cocatalyst, in the following order: AlⁱBu₃ > AlOct₃ > AlEt₃ > AlMe₃, whereas much lower trans-1,4 selectivity was observed in the cases of using MAO and MMAO.     

Post-polymerization modification and organocatalysis using reactive statistical poly(ionic liquid)-based copolymers

Copoly(ionic liquid)s (coPILs) based on poly(styrene)-co-poly(4-vinylbenzylbutylimidazolium) with different anions (Cl⁻ and HCO₃⁻), denoted as PS-co-PVBnBuImCl 1 and PS-co-PVBnBuImHCO₃2, were used as reactive polymers for the purpose of post-polymerization modification and organic catalysis. While coPIL 1 could be derived into the corresponding poly(N-heterocyclic carbene)-silver transition metal complex referred to as poly(NHC–Ag) by a simple deprotonation/metallation sequence utilizing Ag₂O, coPIL 2 was found to quantitatively react with various electrophiles, including CS₂, isothiocyanate and transition metals (based on Pd and Au) upon formal loss of “H₂CO₃, affording the post-functionalized poly(NHC-CS₂), poly(NHC-isothiocyanate) and poly(NHC-Met) (Met = Au, Pd) copolymers. The catalytic activity of both coPILs 1 and 2 was also examined in cyclic carbonate formation by reaction between CO₂ and propylene oxide and in the benzoin condensation, respectively.     

Syntheses and Structural Analytical Studies of Two Co(II) Complexes Based on 1,4-Di(benzimidazole-1-yl)benzene

Two new Co(II) complexes of 1,4-di(benzimidazole-1-yl)benzene ligand (L) with the formulas [(CoLCl₂)(CHCl₃)(DMF)]_∞ (1) and [CoL(NO₃)₂]_∞ (2) have been synthesized by anion-directed self-assembly. Both complexes have been characterized by elemental analyses, IR, and X-ray single crystal diffraction. Complexes 1 and 2 exhibit 1D chain structures. In 1, Co(II) ions possess a distorted tetrahedral coordination environment composed of N₂Cl₂ donors from two L ligands and two chloride ions, while the Co(II) ions in 2 reveal a distorted octahedral structure defined by the N₂O₄ donors from two L ligands and two nitrate anions. These results illustrate that the anions play an important role in the self-assembly of metal–organic materials.     

Crown ethers appended copper tetraazamacrocyclic complexes as receptors for cationic guests

Tetraazamacrocyclic copper(II) complexes linked by the system of conjugated double bonds with one or two benzo-15-crown-5 ether moieties (4Cu and 5Cu) as well as model compounds were synthesized and characterized. The CV of these complexes in acetonitrile (ACN) solution exhibited reversible Cu^II/I redox process. Complexation of Na⁺ and Mg²⁺ cations with 5Cu in the gas phase was confirmed by electrospray mass spectrometry. In solution complexation of Li⁺ and Na⁺ with 5Cu was weak. Complexation of Cl⁻ anion to coordinated copper in 5Cu resulted in an appreciable shift in the Cu^II/I redox potential after addition of studied cations. The addition of increasing amounts of Mg²⁺ cation to the solution of 5Cu resulted in a significant shift of the Cu^II/I reduction process accompanied by further reduction to Cu⁰ followed by replacement of copper by Mg²⁺ cation. Barium(II) cation interacted only with reduced (Cu⁺) form of 5Cu.     

Redox and catalytic properties of new polypyrrole modified electrodes functionalized by [Ru(bpea)(bpy)H2O] complexes; bpea=N,N′-bis(2-pyridylmethyl)ethylamine, bpy=2,2′-bipyridine

New ruthenium(II) complexes containing one or two pyrrole-functionalized polypyridylic ligands have been prepared in order to study their electrochemical behaviour in heterogeneous phase, after anodic polymerization from CH₂Cl₂ solution on an electrode surface. Complexes containing one pyrrole unit have general formula [Ru(bpea-pyr)(bpy)(L)]²⁺ (bpea-pyr=N-[3-bis(2-pyridylmethyl)aminopropyl]pyrrole, bpy=2,2′-bipyridine, L=Cl, complex 3, or L=H₂O, complex 1), whereas compounds having two pyrrole units correspond to [Ru(bpea-pyr)(bpy-pyr)(L)]²⁺ (bpy-pyr=4-methyl-4′-pyrrolylbutyl-2,2′-bipyridine, L=Cl, complex 4, or L=H₂O, complex 2). Upon oxidative polymerization, all complexes form highly stable polypyrrolic films on a graphite disk electrode surface. An electrode modified with complex 2 polypyrrole coating film, C/poly-2, has been tested as heterogeneous catalyst for the oxidation of benzyl alcohol, showing a remarkably high efficiency and notably improving the results obtained with analogous complexes in homogeneous phase.     

Electrocatalytic four-electron reductions of O2 to H2O with cytochrome c oxidase model compounds

Three different complexes, heme-Cu ([(⁶L)Fe^IICu^I]⁺ (1), ⁶L=a binucleating ligand having a heme and covalently tethered copper binding tris(2-pyridyl)methylamine tetradentate moiety), heme complex ((⁶L)Fe^II (4), (with “empty” tethered chelate)), and the “parent” iron-porphyrinate ((F₈TPP)Fe^II (5), F₈TPP=tetrakis(2,6-difluorophenyl)porphyrinate) were employed for the electrocatalytic reduction of O₂. Complexes 1 and 4 reduce O₂ to water (four-electron reduction) with good efficiency (74 and 59%, respectively), but complex 5 exhibited only an ∼20% efficiency, thus primarily the two-electron reduction to hydrogen peroxide occurred. The results of the present electrochemical O₂-reduction studies and the previous studies have elucidated the O₂-binding nature of these three complexes, indicating the formation of quite stable Fe^III(O₂²⁻)Cu^II (peroxo) or Fe^IIIO₂⁻ (superoxo) species. In line with the thinking of other researchers, the fact that both 1 and 4 can well stabilize Fe^IIIO₂⁻ superoxo species may suggest that the formation of the latter is a key to the pathway favoring four-electron reduction of dioxygen to water.     

Thermal behavior of 1,4-bis(4-trimellitimido-2-trifluoromethyl phenoxy)benzene (DIDA) solvated with polar organic solvents and properties of DIDA-based poly(amide-imide)s

Fluorinated diimide-dicarboxylic acid (DIDA, Code: IV), 1,4-bis(4-trimellitimido-2-trifluoromethylphenoxy) benzene, synthesized by reacting 1,4-bis(4-amino-2-trifluoromethyl phenoxy)benzene (I) with trimellitic anhydride in polar solvents (PSv), was found to crystallize easily in amide-type solvents, such as N-methyl-2-pyrrolidinone (NMP), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), or 1,3-dimethyl-2-imidazolidinone (DMI) media, to form a series of stable crystalline solvates (III_(NMP), III_(DMAc), III_DMF), III_(DMI)) containing a certain quantity of crystalline solvent. The solvates III_(PSv) were characterized and proven by DSC, TGA, and X-ray analysis. The decomposition point temperature (T_d) was different with the type of polar solvents in III_(PSv). Elemental analysis and NMR showed that most of the III_(PSv) were formed from IV and polar solvents in the ratio of 1:2, and the solvation processes were found to be reversible. Furthermore, a series of soluble fluorinated poly(amide-imide)s (VI_a-h) were synthesized from reacting either the NMP-solvates III_(NMP) or dry/non-solvates IV with an equivalent amount of diamines by direct polycondensation using triphenyl phosphate and pyridine as condensing agents. Thermal and mechanical properties of the fluorinated VI_a-h were measured, and compared with counterparts of non-fluorinated PAI's (Code: VI′s). In comparison, the fluorinated VI_a-h poly(amide-imide)s exhibited better solubility, tensile, and thermal properties than the non-fluorinated VI′s.     

Enhance the performances of dye-sensitized solar cell by a new type of sensitizer to co-sensitize zinc oxide photoelectrode with ruthenium complex

We designed a new type of sensitizer for dye-sensitized solar cells based on ZnO photoelectrode. Three five-coordinate transition metal complexes [2,6-(ArNCMe)₂C₅H₃NMCl₂·nCH₃CN] (MZn, Cd, Hg) (named as Zn1, Cd1, Hg1), have been synthesized. In all complexes, the metal center is tridentately chelated by the ligand and further coordinated by two chlorine atoms, resulting in distorted trigonal bipyramidal geometry. The improvement in conversion efficiency of dye-sensitized solar cell was achieved by the complexes (M) and N719 co-sensitizing ZnO photoelectrode. In the tandem structure of M/N719/ZnO, the M forms a re-organization of energy level due to its single-crystal structure, which is advantageous to the electron injection and the hole recovery. The result demonstrates the M/N719 co-sensitized solar cell exhibited excellent photovoltaic performances with the short-circuit photocurrent density of 8.943 mA cm⁻², the open-circuit photovoltage of 591 mV and the fill factor of 0.639 under standard global AM 1.5 solar irradiation conditions.     

1D Hydrogen-Bonded Polymers Assembled by Tetraaza Macrocyclic Metal(II) Complexes and Inorganic Salts

The self-assembly of [M(L)]Cl₂·2H₂O (M = Ni²⁺ and Cu²⁺, L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane) with sodium 1,2,4-benzenetricarboxylate (Na₃btcb) and KNO₃ generates the 1D hydrogen-bonded polymers with formulas [Ni(L)(H₂btcb^?)₂] (1) and [Cu(L)(NO₃)₂] (2). These polymer complexes have been characterized by X-ray crystallography, spectroscopy and cyclic voltammetry. The crystal structure of 1 shows a distorted octahedral coordination geometry around the nickel(II) ion, with the four secondary amines of the macrocycle and two carboxylate oxygen atoms of the H₂btcb^? ligand in the trans position. In 2, the coordination environment around the central copper(II) ion reveals an axially elongated octahedron with four Cu–N bonds and two oxygen atoms of the nitrate ligand in the trans position. The cyclic voltammograms of the complexes undergo two one-electron waves corresponding to M^II/M^III and M^II/M^I processes. The electronic spectra and electrochemical behavior of the complexes are significantly affected by the nature of the axial ligands.     

Synthesis of 1,9-bis[glycidyloxypropyl]penta(1′H,1′H,2′H,2′H-perfluoroalkylmethylsiloxane)s and copolymerization with piperazine

A series of 1,9-bis[glycidyloxypropyl]pentasiloxanes (IV-VI) were prepared by the platinum catalyzed hydrosilylation of 1,9-dihydridodecamethylpentasiloxane (I), 1,9-dihydrido-3,5,7-tris(3′,3′,3′-trifluoropropyl)heptamethylpentasiloxane (II), and 1,9-dihydrido-3,5,7-tris(1′H,1′H,2′H,2′H-perfluorooctyl)heptamethylpentasiloxane (III) with allyl glycidyl ether. Subsequently, IV-VI were copolymerized with piperazine to form high molecular weight copoly(carbosiloxane)s (VII-IX). The structures of the 1,9-bis[glycidyloxypropyl]penta-siloxanes (IV-VI) and copoly(carbosiloxane)s (VII-IX) were determined by ¹H, ¹³C, ²⁹Si, and ¹⁹F NMR as well as IR spectroscopy. The molecular weight distributions (M_w/M_n) of VII-IX have been characterized by gel permeation chromatography and their thermal properties measured by differential scanning calorimetry and thermal gravimetric analysis.     

Synthesis and characterization of monomeric and polymeric Cu(II) complexes of 3,4-ethylenedioxythiophene-functionalized with cyclam ligand

A functionalized EDOT derivative with 1,4,8,11-tetraazacyclotetradecane (cyclam) ligand pendant to the ethylene bridge (4) and its complexes [M(4)(BF₄)₂], where M(II) = Cu(II), was prepared and characterized. Their electrochemical copolymerization with EDOT was studied. The electro-co-polymerized films were characterized by electrochemical methods, X-ray photoelectron spectroscopy and by X-ray fluorescence spectroscopy. The co-polymerization method was found to afford a good control of the metal concentration in the polymer matrix and represents a good technique for preparing electronically conductive polymers containing redox-active metal complexes.     

Electrochemical studies of the nickel catecholate complexes for detection of sulphur dioxide gas

Nickel catecholate complexes, bis(diphenylphosphino)ethanenickelcatecholate [(dppe)NiO₂C₆H₃4-R₁] R₁ = CH₃ (1), C(CH₃)₃ (2), H (3) and F (4)] were studied using CV and SWV techniques between −1.5 and +1.5 V at 50 mV s⁻¹ in cathodic and anodic sweeps. Glassy carbon electrode was used with 0.1 M tetrabutylammonium tetrafluroborate (TBATFB) in CH₂Cl₂. Complexes 1-4 before addition of SO₂, showed approximately reversible behaviour (i_pa/i_pc ≈ 1 and ΔE ≈ 77-88 mV); oxidation peaks observed between +313 and +524 mV, reduction peaks between +225 and +436 mV, depending on the substituent on the ligand. Detection limit 0.01 ppm, linear range 0.01-20 ppm, sensitivity 0.02 ppm/mV (with SWV) were obtained. The complexes 1 and 2 could be used as voltammetric sensors while complexes 3 and 4 would be suitable as amperometric sensors, for monitoring industrial SO₂ emissions.     

Colorless and high organosoluble polyimides from 2,5-bis(3,4-dicarboxyphenoxy)-t-butylbenzene dianhydride and aromatic bis(ether amine)s bearing pendent trifluoromethyl groups

A series of polyimides III_a-h characterized by colorlessness, high transparency, high solubility, and good mechanical property, was synthesized from the aromatic dianhydride, 2,5-bis(3,4-dicarboxyphenoxy)-t-butylbenzene dianhydride (I), and various aromatic diamines (II_a-h) with pendent trifluoromethyl group via polyaddition, chemical imidization, and direct cast films. The III series showed more colorless than the polyimides (V and VI series) of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) contained, the VI series was synthesized from the II with 6FDA. These films III had cut-off wavelengths between 371 and 376 nm, as well as b* value (a yellowness index) ranging from 3.0 to 4.7. In fact, it is so far the most colorless aromatic polyimide in our systematical researches. The III series had inherent viscosity ranging from 0.72 to 1.33 dL/g and showed excellent solubility in a variety of organic solvents. They were soluble in a concentration of 5-10% in the amide polar solvent, ether solvent, and chlorinated solvent. These films showed strength tensile of 97-123 MPa, dielectric constants of 2.78-3.28 (1 MHz), and moisture absorptions of 0.11-0.36 wt%. The glass transition temperature of the III series was recorded at 214-259 °C, the 10% weight loss temperature was over 468 °C, and the residue was more than 47% at 800 °C in nitrogen.     

Titanium complexes based on aminodiol ligands for the ring opening polymerization of l- and d,l-lactide

A series of new titanium isopropoxide complexes (1-4-Ti(OⁱPr)₂ based on enantiopure (1-H₂), racemic (2-H₂), meso (3-H₂) and diastereomeric (4-H₂) aminodiol ligands have been prepared and tested as initiators for the ring opening polymerization (ROP) of l/rac-lactide in solution and in bulk conditions. All complexes were shown to have significant activity in solution at 70 °C and higher activity in bulk at 130 °C with a good control over the molar mass distribution and molecular weights. The complex derived from the racemic-aminodiol ligand gave partially heterotactic polylactide in ROP of rac-lactide and afforded atactic polylactide in the bulk, whereas all other complexes yielded atactic polylactides both in solution and in bulk. Ligand variation (chirality) in the complexes has little effect on either the activity or selectivity of the initiators. The polymerization kinetics using (1-Ti(OⁱPr)₂) as an initiator indicated a first order reaction with respect to the monomer concentration.