Novel hydrogen-bonded three-dimensional network complexes containing copper-pyridine-2,6-dicarboxylic acid

The novel complex (H₃O)₂[Cu(2,6-pydc)₂]·H₂O (pydc?=?pyridinedicarboxylic acid) (1) has been synthesized in aqueous solution and characterized by single-crystal X-ray diffraction, elemental analyses and IR spectra. X-ray structural analysis revealed that the novel complex possesses both π–π stacking and hydrogen-bonding interactions for three-dimensional (3D) networks. Crystal data for 1: a?=?13.454(3), b?=?10.266(2), c?= 13.783(3)?Å, α?=?90.00, β?=?115.29(3), γ?=?90.00°, Z?=?3, R ₁?=?0.0423, wR ₂?=?0.1217.     

2,6-Lutidine-N-oxide complexes of rare-earth bromides

2,6-Lutidine-N-oxide (LNO) complexes of rare-earth bromides of the composition wheren = l for M = La, Pr, Nd, Sm, Gd, Ho, Er; andn = 0 for M = Y have been prepared and characterised by analyses, conductance and infrared data. Infrared spectra of the complexes indicate that the coordination of ligand to the metal ion takes place through the oxygen of the ligand, and the water molecule in the complexes present is coordinated to the metal. A coordination number of seven has been suggested to all the rare-earth metal ions.     

The metal complexes of new Schiff bases containing phosphonate groups and catalytic properties for alkane oxidation

In this study, two new salicylidene phosphonate ligands (HL¹ and HL²) and their metal complexes (Cu²⁺, VO²⁺ and La³⁺) were synthesized and characterized by spectroscopic and analytical methods. The molecular structure of the ligand HL¹ was determined by single‐crystal X‐ray diffraction study. In the structure of the ligand, there is an intramolecular phenol‐imine hydrogen bond. The synthesized compounds exhibit only one emission maximum upon excitation at 270–295  nm range. Complexation of the Schiff base ligands with metal ions did not cause a considerable quenching effect. Finally, the complexes prepared were used as catalysts in cyclohexane oxidation under microwave irradiation. The complexes showed high conversion rates (> 90%) for cyclohexane oxidation; however, poor selectivity was observed for all complexes. The La³⁺ complexes showed better selectivity for cyclohexane → cyclohexanol transformation with about 45% selectivity.     

Calculation of catalytic activity of transition metal complexes

A method is proposed for calculation of the catalytic activity of the complexes of transition metals. An effective Hamiltonian describing the behavior of the reagents in the presence of the catalyst is formulated, and a catalytic activity index tan2 is introduced. The isomerization of quadricyclane to norbornadiene is considered. It is shown that the index in the case of the catalytically active low-spin complex CoTPP is two orders of magnitude larger than in the case of the catalytically inactive high-spin complex MnTPP and the analogous Fe(III)TPP and MnPc complexes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 4, pp. 398–406, July–August, 1988.     

Synthesis,characterization and catalytic activity of polymer anchored transition metal complexes toward oxidation reactions

The polymer-anchored Schiff base complexes of Cu(II), Co(II), Ni(II), Mn(II) and Fe(III) were prepared by reacting polystyrene amine with 2-pyridinecarbaldehyde followed by loading of metal atom in methanol. These complexes were characterized by using different physico-chemical and spectroscopic methods. The catalytic activity of these polymer-supported metal catalysts was tested for the oxidation of various olefins and alcohols. Influence of various reaction parameters, such as reaction temperature, reaction time, oxidant, substrate-to-oxidant mole ratio and nature of solvent, was studied for the oxidation of cyclohexene with these catalysts. Among the catalysts studied, Cu-Cat showed higher catalytic activity toward oxidation reactions than the other catalysts. Moreover, hot filtration experiments proved that these catalysts are truly heterogeneous and can be reused a number of times without significant loss of activity.     

聚合负载三氯化镨配合物的合成、表征及催化活性

合成并表征了聚(苯乙烯(S)-丙烯酸(A))镨配合物(SAAC·Pr).红外光谱表明了它的配位结构.计算了共聚物中单体单元的序列分布.苯乙烯和丙烯酸单元长序列分布随其在共聚物中含量的增加而增加.当丙烯酸长序列分布高时,配合物的催化活性低.苯乙烯和丙烯酸的平均链长分别为 nS=3, nA=1时,配合物的催化活性最高.     

Stereospecific synthesis and catalytic activity of L-histidylidene metal complexes

We report on the synthesis, metal coordination, and catalytic impact of histidylidene, a histidine-derived N-heterocyclic carbene (NHC) ligand. The histidinium salt 3, comprising methyl substituents at both heterocyclic nitrogens and protected at the C- and N-terminus of the amino acid, was rhodated and iridated by a transmetallation protocol using Ag(2)O. Ambient temperature and short reaction times were pivotal for full retention of configuration at the α-carbon. The stereospecificity of the reaction was conveniently probed by (31)P NMR spectroscopy after transmetallation with rhodium(I) and coordination of enantiopure (S)-Ph-binepine. The histidylidene rhodium complexes are highly efficient catalysts for the mild hydrosilylation of ketones. For the cationic complexes [Rh(cod)(histidylidene)(phosphine)](+), lowering the temperature shifted the rate-limiting step of the catalytic reaction to an earlier stage that is not enantioselective. Hence the asymmetric induction-which is governed by the chiral phosphine-did not improve at low temperature.     

Catalyzed oxidation of 2,6-dimethylphenol in Triton X- 100 micellar solution

The oxidative coupling reaction of 2,6-dimethylphenol with H2O2 catalyzed by a copper(Ⅱ) Schiff complex in aqueous and Triton X-100 micellar solution under mild conditions was investigated. The kinetics of formation of 3,3′,5,5′-tetramethyl-4,4′-diphenoquinone (DPQ) was studied. Rate constant k2 were obtained. The optimum pH for DPQ generation reaction is 7.25. The main product was DPQ in aqueous buffer solution, but PPE and the oxidized products of PPE remained in Triton X-100 micellar solution.     

Manganese(II) complexes of hydrazone based NNO-donor ligands and their catalytic activity in the oxidation of olefins

The reaction between tridentate NNO donor hydrazone ligands, (E)-2-cyano-N′-(phenyl(pyridin-2-yl)methylene)acetohydrazide (HL¹) and (E)-2-cyano-N′-(1-(pyridin-2-yl)ethylidene)acetohydrazide (HL²), with MnCl₂·4H₂O in methanol resulted in [Mn(HL¹)Cl₂(CH₃OH)] (1) and [Mn(HL²)Cl₂(CH₃OH)] (2). Molecular structures of the complexes were determined by single-crystal X-ray diffraction. All of the investigated compounds were further characterized by elemental analysis, FT-IR, TGA, and UV–Vis spectroscopy. These complexes were used as catalysts for olefin oxidation in the presence of tert-butylhydroperoxide (TBHP) as an oxidant. Under similar experimental conditions with equal manganese loading, the presence of [Mn(HL²)Cl₂(CH₃OH)] (2) resulted in higher conversion than [Mn(HL¹)Cl₂(CH₃OH)] (1).     

聚合物载体-稀土金属配合物的研究IV.含亚硫酰基聚合物载体-稀土金属配合物的合成,表征及其催化活性

Styrene-2-(methylsulfinyl)ethyl methacrylate copolymer-supported MCl3 complexes, where M = La, Pr, Nd, Eu, Ho, Er, Tm, and Yb, were prepared and characterized by IR spectroscopy. The catalytic activity of the polymer-supported NdCl3-(iso-Bu)3Al system towards stereospecific polymerisation of butadiene was 2-3 times higher than that of NdCl3-(iso-Bu)3Al-DMSO system. The cis-1,4 content of polybutadiene formed was >98%.     

Thermal degradation kinetics of polyimide containing 2,6-benzobisoxazole units

A novel polyimide (PI) based on 2,6-bis(p-aminophenyl)-benzo[1,2-d;5,4-d′]bisoxazole has been synthesized via a conventional two-stage procedure with bis(ether anhydrides) (HQDPA). The intermediate poly(amic acid) had inherent viscosities of 1.70 dl/g and could be thermally converted into light yellow polyimide film. The resulted polyimide showed excellent thermal stability, and the glass transition temperatures (T_g) were above 283 °C, the 5% weight loss temperature of the polymer was at 572 °C in N₂. The thermal degradation of the polyimide was studied by thermogravimetric analysis (TGA) in order to determine the actual reaction mechanisms of the decomposition process. The activation energy of the solid-state process was determined using Flynn-Wall-Ozawa method, which does not require knowledge of the reaction mechanism, which resulted to be 361.36 kJ/mol. The activation energy of different mechanism models and pre-exponential factor (A) were determined by Coats-Redfern method. Compared with the value obtained from the Ozawa method, the actual reaction mechanism obeyed nucleation and growth model, Avrami-Erofeev function (A₃) with integral form g(X) = [−ln(1−X)]³.     

Copper(II) complexes with pyridine-2,6-dicarboxylic acid from the oxidation of copper(I) iodide

Via an oxidation reaction of Cu(I) iodide with pyridine-2,6-dicarboxylic acid (H₂L) in DMF three copper(II) complexes, [(CH₃)₂NH₂]₂[CuL₂] (1), K₂[CuL₂]?H₂L?H₂O (2) and [Cu(L)(H₂O)]_n (3), were synthesized and characterized. The structures of 1–3 were determined by single crystal X-ray diffraction studies. In-situ DMF decomposition produces dimethylamine base under solvothermal conditions and a proton transfer reaction takes place for the complex formation of 1. 3-D networks are stabilized in 1 and 2 via hydrogen bonds. Complex 3 is a 1-D coordination polymer with Cu-O semi-coordination bonds. Thermal decomposition of the complexes results in the corresponding metal oxides. Also, the electrochemical behavior of 1 was determined to be a metal-centered and diffusion-controlled, one-electron reduction process.     

Synthesis,characterization, and antibacterial activity of yttrium(III) complexes with 2,6-pyridinedicarboxylate and pyridine

A series of metal coordination complexes of yttrium(III) containing 2,6-pyridinedicarboxylate and pyridine have been prepared with different molar ratios of yttrium(III) to 2,6-pyridinedicarboxylate in aqueous pyridine solutions, and characterized by elemental analysis, infrared spectra, nuclear magnetic resonance, and thermal analyses. The in vitro antibacterial activities of the complexes have also been investigated against microorganisms such as Gram-negative bacteria Bacillus coli and Gram-positive bacteria Staphylococcus aureus by the disc diffusion method in DMSO. When compared to previous results, the yttrium(III) complexes of 2,6-pyridinedicarboxylate and pyridine have a moderate effect on microorganisms due to the presence of the pyridine group.     

Redox, thermodynamic and spectroscopic of some transition metal complexes containing heterocyclic Schiff base ligands

Complexes of two series of Schiff base ligands, H₂L_a and H₂L_bderived from the reaction of 2,6-diacetyl pyridine with semicarbazide, H₂L_a and thiosemicarbazide, H₂L_b, with the metal ions, Co(II), Ni(II), Cu(II), VO(IV) and UO₂(VI) have been prepared. The ligands are characterized by elemental analysis, IR, UV–vis and ¹H NMR. The structures of the complexes are investigated with the IR, UV–vis, X-band ESR spectra, ¹H NMR and thermal gravimetric analysis as well as conductivity and magnetic moment measurements. The IR-spectra reveal the presence of variable modes of chelation for the investigated ligands. A variety of binuclear or mononuclear complexes were obtained with the two ligands in tri-, tetra or pentadentate forms. The bonding sites are the pyridine nitrogen, two azomethine nitrogen atoms and ketonic oxygen in case of H₂L_a or sulphur atoms in case of H₂L_b. The Coats–Redfern equation has been used to calculate the kinetic and thermodynamic parameters for the different thermal decomposition steps of some complexes. Cyclic voltammograms of Co(II) and Ni(II) show quasi-reversible peaks. The redox properties and the nature of the electro-active species of the complexes have been characterized.     

Dinuclear metal complexes of Schiff base ligands as catalysts for oxidation and epoxidation reactions

Dinuclear copper(II) complexes (Cu₂ L_nCl₃), nickel(II) complexes (Ni₂ L_nCl₃) and cobalt(II) complexes (Co₂L ₂ ⁿ Cl₂) from Schiff base ligands are synthesised, characterised and used as catalysts for oxidation of 3,5-DTBC to 3,5-DTBQ. (Cu₂L_nCl₃) are found to be more efficient than the other complexes. Dinuclear iron(III) complexes of composition (Fe₂L₂Cl₂) and ruthenium (III) complexes of composition Ru₂L ₂ ⁿ Cl₆(PPh₃)₂ and Ru₂L ₂ ⁿ Cl₂(PPh₃)₂ catalyse epoxidation of styrene and cyclohexene. Catalytic activities of ruthenium(III) complexes are much greater than those of analogous iron(III) complexes.     

2,6-Dimethylphenol polymerization with cuprous chloride and n-butylamine catalyst system: Effect of Nal addition

2,6-Dimethylphenol polymerization with catalyst systems based on CuCl/n-butylamine were studied under 10 kg/cm² pure oxygen pressure. By addition of sodium iodide, the catalyst performance was dramatically improved and an unusual long induction period was observed. Both the polymer intrinsic viscosity obtained and the induction period increased significantly with the increase of NaI concentration. However, the induction period decreased rapidly with the increase of n-butylamine concentration. UV-VIS absorption spectra showed that the CuCl/n-butylamine complex was converted to Cul/n-butylamine complex after the addition of NaI. The hydration rate of copper halide/n-butylamine complex decreased significantly with the increase of NaI and n-butylamine concentrations. Therefore the increase of polymer intrinsic viscosity and induction period by NaI addition suggest that the polymerization catalyst became more hydrolytically stable and less active at the higher NaI concentration. © 1996 John Wiley & Sons, Inc.     

Volcano correlations for the reactivity of surface-confined cobalt N<Subscript>4</Subscript>-macrocyclics for the electrocatalytic oxidation of 2-mercaptoacetate

We have investigated the electrocatalytic activity of several substituted and unsubstituted cobalt–phthalocyanines of substituted tetraphenyl porphyrins and of vitamin B₁₂, for the electro-oxidation of 2-mercaptoacetate, with the complexes pre-adsorbed on a pyrolytic graphite electrode. Several N4-macrocyclic were used to have a wide variety of Co(II)/(I) formal potentials. The electrocatalytic activity, measured as current at constant potential, increases with the Co(II)/(I) redox potential for porphyrins as Co–pentafluorotetraphenylporphyrin < Co–tetrasulfonatotetraphenylporphyrin < Co-2,2′,2″,2‴tetra-aminotetraphenylporphyrin and decreases for cobalt phthalocyanines as Co-3,4-octaethylhexyloxyphthalocyanine > Co–octamethoxyphthalocyanine > Co–tetranitrophthalocyanine Co–tetraaminophthalocyanine > Co–unsubstituted phthalocyanine > Co–tetrasulfonatophthalocyanine > Co–perfluorinated phthalocyanine. Vitamin B₁₂ exhibits the maximum activity. A correlation of log I (at constant potential) versus the Co(II)/(I) formal potential of the catalysts gives a volcano curve. This clearly shows that the search for better catalysts for this reaction point to those N₄-macrocyclic complexes with Co(II)/(I) formal potentials close to −0.84 V versus SCE, which correspond to an optimum situation for the interaction of the thiol with the active site. Dedicated to Prof. Dr. Teresa Iwasita on the occasion of her 65th birthday in recognition of her numerous contributions to interfacial electrochemistry.