Synthesis,crystal structure and electrocatalytic activity of discrete and polymeric copper(II) complexes with bitopic bis(pyrazol-1-yl)methane ligands

New coordination copper(II) compounds containing bitopic bis(pyrazol-1-yl)methane ligands, namely 1,1,2,2-tetrakis(pyrazol-1-yl)ethane, 1,4-bis[bis(pyrazol-1-yl)methyl]benzene and 1,4-bis[bis(3,5-dimethylpyrazol-1-yl)methyl]benzene were prepared. Reactions of ligands with Cu^2 + ions in 1:2 ratio gave discrete homodinuclear complexes, while 1:1 ligand-to-metal ratio lead to the formation of coordination polymers. Electrocatalytic activity of compounds in oxygen electroreduction reaction on the surface of modified carbon paste electrode was evaluated.     

Carbon dioxide/propylene oxide coupling reaction catalyzed by chromium salen complexes

A series of chromium/Schiff base complexes N,N′-bis(salicylidene)-1,2-phenylenediamino chromium^III X were prepared and employed for the alternating copolymerization of carbon dioxide with racemic propylene oxide in the presence of (4-dimethylamino)pyridine. The effect of the complex structure and reaction conditions on the catalytic activity, the poly(propylene carbonate)/cyclic carbonate (PPC/PC) selectivity, and the polymer head-to-tail linkages was examined. The experiments indicated that N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-phenylenediamino chromium^III (NO₃) exhibited the highest PPC/PC selectivity as well as polymer head-to-tail linkages and N,N′-bis(3,5-dichlorosalicylidene)-1,2-phenylenediimino chromium^III (NO₃) possessed the highest catalytic activity among these chromium/Schiff base complexes. The structure of the produced copolymer was characterized by the IR, ¹H NMR, and ¹³C NMR measurements. Almost 100% carbonate content of the resulting polycarbonate were obtained with the help of these effective catalyst systems under facile conditions.     

Eu(OTf)3-catalyzed oxidation of 5-alkylidene-4,5-dihydrofurans: A new approach to functionalized furylhydroperoxides

Here reported is an unusual catalytic ability of Eu(OTf)₃ in the oxidative conversion of 5-alkylidene-4,5-dihydrofuran derivatives in the corresponding furylhydroperoxides with tert-butyl hydroperoxide. Furthermore, an enantioselective process of disproportionation of furylhydroperoxides has been highlighted in the presence of the Jacobsen’s catalyst (S,S)-(+)-N,N′-Bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) chloride.     

Asymmetric oxidative coupling polymerization of dihydroxynaphthalene derivatives with cobalt-salen complexes

Summary The oxidative coupling polymerization of dihydroxynaphthalene derivatives with a novel catalyst system, the cobalt(II)-salen complexes, was investigated. For example, the asymmetric polymerization of 2,3-dihydroxynaphthalene with (R,R)-(–)-N,N’-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminocobalt(II) in a dichloromethane-methanol mixed solvent at room temperature for 0.5 h under an oxygen atmosphere, followed by acetylation of the hydroxyl groups, produced a methanol-insoluble polymer with the specific rotation value [α]_D of +165, which was rich in the R-configuration. To estimate the enantioselectivity during the polymerization, the corresponding acetylated dimer product was isolated from a polymerization mixture and determined to be 58% e.e.     

Effect of some tripodal bipyrazolic compounds on C38 steel corrosion in hydrochloric acid solution

The corrosion inhibition of C38 steel in molar HCl by N,N-bis[2-(3,5-dimethyl-1H-pyrazol-1-yl)ethyl]buthylamine (P1) and 5-{N,N-bis[2-(3,5-dimethyl-1H-pyrazol-1-yl)ethyl] amino} pentanol (P2) has been investigated at 308 K using electrochemical and weight loss measurements. Measurements show that these compounds act as good inhibitors without changing the mechanism of the corrosion process. Moreover, the inhibiting efficiency increases with the increase in concentration of the studied inhibitors. Compound P2 showed better protection properties even at relatively higher temperatures when compared to P1. The associated activation corrosion and free adsorption energies have been determined. P1 and P2 are adsorbed on the C38 steel surface according to a Langmuir isotherm adsorption model.     

Multinuclear Cu(II) Schiff Base Complex as Efficient Catalyst for the Chemical Coupling of CO2 and Epoxides: Synthesis, X-ray Structural Characterization and Catalytic Activity

Abstract  

The synthesis, X-ray structure, spectroscopic and catalytic properties of sterically hindered Schiff-base ligands (L₁H = N-[allylamine]-3,5-di-tert-butyl salicylaldimine, L₂H=N-[2-amino-5-methyl pyridine]-3,5-di-tert-butyl salicylaldimine and L₃H=N-[2-amino-6-methyl pyridine]-3,5-di-tert-butyl salicylaldimine), and their mononuclear Cu(II) complex for L₁H with multinuclear Cu(II) complexes for L₂H and L₃H, were described. The copper(II) complexes of these ligands were synthesized by treating an methanolic solution of the appropriate ligand with an appropriate amount of CuCl₂·2H₂O. The ligands and their copper(II) complexes were characterized by FT-IR, UV–Vis, ¹H-NMR, elemental analysis, measurement of room temperature magnetic moment, and X-ray structural determination. The reaction of the L₂H and L₃H ligands in a 1:1 mol ratio with CuCl₂·2H₂O afforded ionic copper metal(II) complexes in the presence of NEt₃. The Cu(II) metal complexes tested as catalysts for the formation of cyclic organic carbonates from carbon dioxide and liquid epoxides which served as both reactant and solvent. [Cu₃(L₂)₄]Cl₂·CuCl₂ complex which has 5-methyl substituent on the pyridine ring showed high catalytic activity for chemical coupling carbon dioxide with epoxides (propylene oxide (PO), epichlorohydrine (EC) and 1,2-epoxy butane (EB)) selectively.     

Synthesis and reactivity of antioxidants based on vernolic acid and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid

The reactivity of sterically hindered phenols toward free radicals of the hydrocarbon cumene was studied. New compounds, i. e. methyl cis-13(12)-{3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxy}-12(13)-hydroxyoleate and cis-13(12)-{3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxy}-12(13)-hydroxyoleic acid were synthesized starting from vernolic acid and its methyl ester, respectively, and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid. Both new compounds possess antioxidant activities similar to those of commercially available antioxidants.     

New mononuclear CuII and ZnII complexes capable of stabilizing phenoxyl radicals as models for the active form of galactose oxidase

Herein, we describe the synthesis and crystal structure of mononuclear Cu^II and Zn^II complexes containing the new pentadentate H₂L ligand (H₂L = N-(methyl)-N^′-(2-pyridylmethyl)-N,N^′-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-1,3-propanediamine. The [Cu^II(L)] and [Zn^II(L)] complexes and their one-electron oxidized [Cu^II]⁺ ([1]⁺) and [Zn^II]⁺ ([2]⁺) compounds exhibit electrochemical and spectroscopic (UV–Vis and EPR) features with relevant insight into the oxidizing half-reaction of the metalloenzyme galactose oxidase.     

Synthesis,reactivity, and X-ray structural characterization of a vanadium(III) oxidation pre-catalyst, (CpPOEtCo)VCl2(DMF)

Vanadium complexes are extensively used in the chemical industry as oxidation catalysts. During the course of our investigations into vanadium oxidation catalysis, the rich reactivity of a vanadium(III) scorpionate analogue complex, (CpP^OEtCo)VCl₂(DMF) (1), was investigated. The octahedrally coordinated 1 was prepared by mixing vanadium(III) chloride with Na(CpP^OEtCo) in DMF. The crystal structure of 1 has been determined through X-ray diffraction. Complex 1, C₂₀H₄₂Cl₂CoNO₁₀P₃V, crystallizes in the monoclinic space group P2₁/c with a = 38.566(9) Å, b = 9.499(2) Å, c = 18.149(4) Å, and β = 100.485(4)° with Z = 8. Complex 1 was found to be an effective pre-catalyst for the oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone. The reactivity studies, oxidative catalytic ability, as well as X-ray structural characterization of (CpP^OEtCo)VCl₂(DMF) will be discussed. ((CpP^OEtCo) = [η⁵-cyclopentadienyltris(diethylphosphito-κ¹P) cobaltate(III)⁻; DMF = N,N-dimethylformamide).     

Electrochemistry of di-tert-butylphosphinopentaphenylferrocene (Q-phos) and derivatives

The oxidative electrochemistry of 1-di-tert-butylphosphino-1′,2′,3′,4′,5′-pentaphenylferrocene (Q-phos), 1-di-tert-butylphosphino-1′,2′,3′,4′,5′-penta(4-trifluoromethylphenyl)ferrocene (Q-phos-CF₃), 1-di-tert-butylphosphino-1′,2′,3′,4′,5′-penta(4-methoxyphenyl)ferrocene (Q-phos-OMe) and 1-di-tert-butylphosphino-1′,2′,3′,4′,5′-penta(4-methylphenyl)ferrocene (Q-phos-Me) was explored. All of the compounds undergo a reversible oxidation, and the formal potentials are sensitive to the R groups on the phenyl rings.     

Saccharide derived dinuclear Cu(II) complex: An efficient catalyst for oxidation of catechol and benzylic alcohols

Catalytical aspect of 4,6-O-ethylidene-β-D-glucopyranosylamine derived dinuclear Cu(II) complex has been explored. The complex exhibits good catecholase like activity and oxidizes model substrate 3,5-di-tert-butylcatechol to 3,5-di-tert-butyl-o-quinone. The complex also acts as selective catalyst to oxidize the primary and secondary alcohols to corresponding carbonyl compounds in excellent yield (65–82%) under mild conditions.     

Synthesis and characterization of 1-(3,5-di-tert-butyl)pyrazolyldiphenylphosphine and its gold(I) complex

1-(3,5-Di-tert-butyl)pyrazolyldiphenylphosphine was prepared from 3,5-di-tert-butyl)pyrazole and chlorodiphenylphosphine. It reacted with (Me₂S)AuCl to afford a Au(I) complex bearing the pyrazolylphosphine ligand in a monodentate coordination mode.     

Sensing metal ions with two new azomethine–thiophene pincer ligands (NSN): Fluorescence and MALDI-TOF-MS applications

The two new pincer azomethine–thiophene ligands (N,NE′,N,NE′)-N,N′-(thiophene-2,5-diylbis(methan-1-yl-1-ylidene))bis(naphathalen-2-ylmethanamine) (L1) and (E)-(4,6-dihydropyren-1-yl)-N-((5-((E)-(pyren-1-ylmethylimino)ethyl)thiophen-2-yl)methylene)methanamine (L2), their absorption, fluorescence and MALDI-TOF-MS spectroscopic studies are described. The two systems synthesised combine the emissive probes pyrene and naphthyl with the good chelating properties of a tridentate SN₂ donor-set from a thiophene Schiff-base ligand. Both ligands gave analytically pure solid complexes with Ni(II) and Pd(II) salts. The bichromophoric pyrene derivative L2 presents two emission bands in solution, one corresponding to the monomer species and a red-shifted band attributable to the intramolecular excimer. Ni(II) and Pd(II) complexation affects the conformation in solution, increasing the monomer emission at the expense of the excimer band; this effect could be explored in metal ion sensing. System L1 behaves as a non emissive probe. In situ complexation reactions followed by MALDI-TOF-MS spectrometry without matrix support have also been performed; these experiments show that L1 could be a potential chemosensor for Ni(II) and Pd(II).     

Complexation of poly(pyrrole-EDTA like) film modified electrodes: Application to metal cations electroanalysis

Complexing polymer-coated electrodes have been synthesized by oxidative electropolymerization of N,N′-ethylenebis[N-[(3-(pyrrole-1-yl)propyl) carbamoyl) methyl]-glycine] (L). There were used for the electrochemical detection of Cu(II), Pb(II) and Cd(II) ions by means of the chemical preconcentration-anodic stripping technique. For thick polymeric binding materials and long accumulation times, competitive experiments showed that the polyL film modified electrodes are selective towards Cu(II) ions and particularly insensitive to the presence of Cd(II). In contrast, imprinted polymer-coated electrodes prepared by electropolymerization of the Cd(II) complex of L allowed an efficient complexation and sensing of Cd(II) cations. The selectivity of the molecular electrode materials can thus be subtly modulated upon playing on the accumulation time and on the pre-structuration of the complexing polymers.     

Novel hexanuclear and octanuclear zinc alkyl cages derived from a bis-oxamidate ligand

1 and 2 were prepared by coordination self-assembly from reacting N,N′-bis(3,5-di-tert-buthyl-2-phenol)oxamide (L-H₄) with ZnEt₂ in toluene and THF, respectively. The molecular X-ray structures show 1 as an octanuclear Zn₈ cage and 2 as a hexanuclear Zn₆ cage. The nuclearity of these cages is driven by the solvent, in fact 1 gives 2 upon addition of THF. Good polymer conversions for the ROP of rac-lactide were achieved by using 1 and 2 with alcohols as co-catalysts.     

Synthesis and electrocatalytic function for hydrogen generation of cobalt and nickel complexes supported by phenylenediamine ligand

To study the effect of different metal centers on catalytic function, two complexes [L-M] (M = Co, 1; Ni, 2) were prepared by the reactions of N,N′-bis(2-amino-3,5-di-tert-butylphenyl)-o-phenylenediamine, H₂L, with Co(ClO₄)₂·6H₂O or Ni(ClO₄)₂·6H₂O, respectively. Electrochemical investigations show 1 and 2 can electrocatalyze hydrogen generation both from acetic acid and aqueous buffer. Complexes 1 and 2 afford a turnover frequency (TOF) of 738.23 and 1331.23 mol of hydrogen per mole of catalyst per hour (mol h^− 1) at an overpotential (OP) of 0.838 V from a neutral buffer, respectively, indicating that the nickel center constitutes the better active catalyst.     

New fluorinated poly(1,3,4-oxadiazole-ether-imide)s

New fluorinated poly(1,3,4-oxadiazole-ether-imide)s have been prepared by solution polycondensation reaction of different aromatic diamines having preformed 1,3,4-oxadiazole ring, such as 2,5-bis(p-aminophenyl)-1,3,4-oxadiazole, 2,5-bis[p-(4-aminophenoxy)phenyl]-1,3,4-oxadiazole, 2,5-bis[p-(3-aminophenoxy)phenyl]-1,3,4-oxadiazole, 2-(4-dimethylaminophenyl)-5-(3,5-diaminophenyl)-1,3,4-oxadiazole and 2-(4-fluorophenyl)-5-(3,5-diaminophenyl)-1,3,4-oxadiazole, with an aromatic dianhydride incorporating ether linkages and hexafluoroisopropylidene group, namely 1,1,1,3,3,3-hexafluoro-2,2-bis-[(3,4-dicarboxyphenoxy)phenyl]-propane dianhydride. The polymers were easily soluble in polar organic solvents, such as N-methylpyrrolidinone, N,N-dimethylformamide, and pyridine, as well as in certain low boiling-point organic solvents, such as tetrahydrofuran and chloroform. Very thin coatings deposited onto silicon wafers exhibited smooth, pinhole-free surface in atomic force microscopy. The polymers showed high thermal stability with decomposition temperature being above 410 °C. They exhibited a glass transition in the temperature range of 183-217 °C, with reasonable interval between glass transition and decomposition temperature. Solutions of some polymers in N,N-dimethylformamide exhibited blue fluorescence, having maximum emission wavelength in the range of 411-424 nm.     

Oxotungsten(VI) complexes with amino(phenolate)alcoholate ligand

The reaction between tungsten(VI) complex [W(eg)₃] (eg = 1,2-ethanediolato dianion) and a phenolic ligand precursor 2,4-di-tert-butyl-6-(((2-hydroxyethyl)(methyl)amino)methyl)phenol (H₂L) affords a monomeric oxotungsten complex [WO(eg)(L)]. This complex reacts further with Me₃SiCl, which leads to the displacement of ethanediolato ligand from the complex unit and formation of cis- and trans-isomers of corresponding dichloro complex [WOCl₂(L)]. Identical dichloro complexes were also prepared by the reaction between H₂L and WOCl₄. Molecular structure of [WO(eg)(L)] was verified by X-ray crystallography.     

Synthesis and characterization of iron(II) and iron(III) complexes with a tridentate O,N,O′-ligand

The coordination chemistry of the ligand precursor 1-benzoyl-4,5-dihydro-3,5-bis(trifluoromethyl)-1H-pyrazol-5-ol (1a) to iron(II) acetate was studied. In dependence of the added co-ligand different complex geometries were observed. In case of 4-dimethylaminopyridine (DMAP) as co-ligand an octahedral iron(II) complex was found with an O,N,O′-coordination of the tridentate ligand (1a-2H), in which the ligand is planar, the oxygen donors are trans to each other, and the nitrogen donor is in a cis position. The other coordination sites on the iron center are occupied by DMAP ligands. In contrast to that, with triphenylphosphane as the co-ligand an oxidation process took place, which revealed an octahedral iron(III) complex with a comparable geometry for the tridentate ligand (O,N,O′-coordination, 1a-2H) demonstrating the usefulness of 1a-2H to stabilize different oxidation states. The additional coordination sites are occupied by one triphenylphosphane oxide and ethoxide ligands. Interestingly, the ethoxide ligands act as bridging ligands to form a bimetallic complex.     

Alumina-supported Mn(II), Co(II), Ni(II) and Cu(II) N,N-bis(salicylidene)-2,2-dimethylpropane-1,3-diamine complexes: Synthesis, characterization and catalytic oxidation of cyclohexene with tert-butylhydroperoxide and hydrogen peroxide

New square-planar manganese(II), copper(II), nickel(II) and cobalt(II) complexes of a tetradentate Schiff-base ligand “N,N-bis(salicylidene)-2,2-dimethylpropane-1,3-diamine, H₂[salpnMe₂]” have been prepared and characterized by elemental analyses, IR, UV–Vis, conductometric and magnetic measurements. The results suggest that the symmetrical Schiff-base is a bivalent anion with tetradentate N₂O₂ donors derived from the phenolic oxygen and azomethine nitrogen. The formulae was found to be [M(salpnMe₂)] for the 1:1 non-electrolytic complexes. Alumina-supported metal complexes (ASMC; [M(salpnMe₂)/Al₂O₃]) catalyze the oxidation of cyclohexene with tert-buthylhydroperoxide (TBHP) and hydrogen peroxide. Oxidation of cyclohexene with TBHP gave 2-cyclohexene-1-one, 2-cyclohexene-1-ol and 1-(tert-butylperoxy)-2-cyclohexene whereas, oxidation with H₂O₂ resulted in the formation of cyclohexene oxide and cyclohexene-1,2-diol. Manganese(II) complex supported on alumina “[Mn(salpnMe₂]–Al₂O₃” shows significantly higher catalytic activity than other catalysts.