Copper(II) Schiff Base Complex Immobilized on Superparamagnetic Fe3O4@SiO2 as a Magnetically Separable Nanocatalyst for Oxidation of Alkenes and Alcohols

A new heterogeneous catalyst containing a copper(II) Schiff base complex covalently immobilized on the surface of silica‐coated Fe₃O₄ nanoparticles (Fe₃O₄@SiO₂‐Schiff base‐Cu(II)) was synthesized. Characterization of this catalyst was performed using various techniques. The catalytic potential of the catalyst was investigated for the oxidation of various alkenes (styrene, α‐methylstyrene, cyclooctene, cyclohexene and norbornene) and alcohols (benzyl alcohol, 3‐methoxybenzyl alcohol, 3‐chlorobenzyl alcohol, benzhydrol and n ‐butanol) using tert ‐butyl hydroperoxide as oxidant. The catalytic investigations revealed that Fe₃O₄@SiO₂‐Schiff base‐Cu(II) was especially efficient for the oxidation of norbornene and benzyl alcohol. The results showed that norbornene epoxide and benzoic acid were obtained with 100 and 87% selectivity, respectively. Moreover, simple magnetic recovery from the reaction mixture and reuse for several times with no significant loss in catalytic activity were other advantages of this catalyst     

Novel cobalt(Ⅱ) complexes of amino acids-Schiff bases catalyzed aerobic oxidation of various alcohols to ketones and aldehyde

<正>Two cobalt(Ⅱ) complexes 1 and 2 of Schiff bases derived from amino acids were synthesized and used for oxidation of benzyl alcohol with molecular oxygen at different conditions of pH,solvent,temperature and complex/alcohol molar ratio to optimize reaction conditions and to evaluate the catalytic efficiency of new cobalt Schiff base complexes.Under obtained optimum conditions,various alcohols were oxidized to corresponding aldehydes and ketones.     

Electrochemical behavior and voltammetric determination of cysteine and cystine at carbon-paste electrodes modified with metal phthalocyanines

The electrochemical behavior of cysteine and cystine on carbon-paste electrodes modified with Fe(II), Co(II), Ni(II), and Cu(II) phthalocyanines is studied. Metal phthalocyanines exhibit catalytic activity in the electrooxidation of cysteine and cystine and in the reduction of cystine. The best catalyst is the cobalt complex. In the electrooxidation of cysteine, the catalysts are electrogenerated complex species of Co(II)Pc or Co(III)Pc⁺, and in the oxidation of cystine, oxidized or reduced forms of the coordinated ligand. Various versions of the determination of cysteine and cystine by the electrocatalytic reactions on the modified electrodes are proposed.     

Catalytic evaluation of copper (II) N-salicylidene-amino acid Schiff base in the various catalytic processes

N-Salicylidene amino acid Schiff base sodium sulfonate salt, as a tridentate dibasic chelating ligand, was obtained from the common condensation of salicylaldehyde-5-sodium sulfonate with tyrosine (HPST). The internal formed ligand coordinated to Cu²⁺ ion in an aqueous media affording new Cu (II)-complex (Cu-PST), which characterized by various physico-chemicals spectral tools. The mononuclear complex was evaluated as a homogeneous and heterogeneous catalyst in the (ep)oxidation protocols of 1,2-cyclooctene and benzyl alcohol. Heterogeneously, Cu-PST was immobilized on Fe₃O₄-SiO₂, as nanoparticles. The heterogeneous catalyst was characterized by infrared, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, Brunauer−Emmett−Teller and magnetism. Homogeneously, the temperature, solvent and oxidant influences were examined in the catalytic reactions to realize the best reaction conditions. Cu-catalyst exhibited better catalytic performance in the (ep)oxidation processes homogeneously than that in the heterogeneous phase at 80°C for 2 hr in acetonitrile. Reusability of the homogeneous catalyst was for a maximum of three times in the (ep)oxidation reaction, whereas the heterogeneous catalyst was active for six times. A mechanistic pathway was proposed for both catalysts, comparatively.     

Facile synthesis of highly active Co(II) and Fe(II) phthalocyanine catalysts for aerobic oxidation of phenolic compounds

In this work, 2,3-dichlorophenoxy substituted cobalt and iron phthalocyanines have been synthesized and used as efficient catalysts for aerobic oxidation of nitrophenols. Co(II) and Fe(II) phthalocyanines have been characterized by IR, ¹H NMR, ¹³C NMR, UV–vis, and mass spectroscopies. tert-butyl hydroperoxide (TBHP), m-chloroperoxybenzoic acid, hydrogen peroxide, and air oxygen have been used as oxygen source. These catalysts offered the highest activity on 4-nitrophenol oxidation in 3 h. In order to achieve the best reaction conditions, oxidant ratio, temperature, and oxidant type have been investigated with different nitrophenols in 3 h.     

Efficient and recyclable novel Ni‐based metal–organic framework nanostructure as catalyst for the cascade reaction of alcohol oxidation–Knoevenagel condensation

A novel Ni‐based metal–organic framework (Ni‐MOF) with a Schiff base ligand as an organic linker, Ni₃(bdda)₂(OAc)₂?6H₂O (H₂bdda = 4,4′‐[benzene‐1,4‐diylbis(methylylidenenitrilo)]dibenzoic acid), was synthesized and characterized using powder X‐ray powder diffraction, thermogravimetric analysis, Brunauer–Emmett–Teller measurements, inductively coupled plasma atomic emission spectroscopy, transmission electron microscopy, elemental analysis and Fourier transform infrared spectroscopy. The synthesized Ni‐MOF exhibited a high catalytic activity in benzyl alcohol oxidation using tert‐butyl hydroperoxide under solvent‐free conditions. Also, the efficiency of the catalyst was investigated in the cascade reaction of oxidation–Knoevanagel condensation under mild conditions. The Ni‐MOF catalyst could be recovered and reused four times without significant reduction in its catalytic activity.     

Studies on Phenol Oxidation with H2O2 Catalyzed by Schiff Base Cobalt(II) Complexes in Micellar Solution

The two Schiff base cobalt(II) complexes, CoL¹ and CoL², were synthesized and characterized. The metallomicelle made up of the cobalt(II) complexes and surfactants (CTAB, LSS and Brij35), as mimic peroxidase metalloenzyme, were used in the catalytic oxidation of phenol by H₂O₂. The mechanism and a kinetic mathematic model of the phenol catalytic oxidation were studied. The acid effect of reaction system, structural effect of the complexes, and effect of temperature on the rate of the phenol oxidation catalyzed by the mimetic peroxidases have been discussed. The results showed that the schiff base cobalt(II) complexes and their metallomicelles as peroxidase mimics exhibit good catalytic activity and similar catalytic character to natural enzyme.     

Synchronizing Steric and Electronic Effects in {RuII(NNNN,P)} Complexes: The Catalytic Dehydrative Alkylation of Anilines by Using Alcohols as a Case Study

A series of new hexacoordinated {Ru^II(NNNN,P)} complexes was prepared from [RuCl₂(R₃P)₃]. Their structure was determined by X‐ray crystallography. The catalytic potential of this new class of complexes was tested in the alkylation of aniline with benzyl alcohol. In this test reaction, the influence of the counteranion plus electronic influences at the tetradentate ligand and the phosphine ligand were examined. The electrochemistry of all complexes was studied by cyclic voltammetry. Depending on the substituent at the ligand backbone, the complexes showed a different behavior. For all N‐benzyl substituted complexes, reversible Ru^II/III redox potentials were observed, whereas the N‐methyl substituted complex possessed an irreversible oxidation event at small scan rates. Furthermore, the electronic influence of different substituents at the ligand scaffold and at the phosphine on the Ru^II/III redox potential was investigated. The measured E₀ values were correlated to the theoretically determined HOMO energies of the complexes. In addition, these HOMO energies correlated well with the reactivity of the single complexes in the alkylation of aniline with benzyl alcohol. The exact balance of redox potential and reactivity appears to be crucial for synchronizing the multiple hydrogen‐transfer events. The optimized catalyst structure was applied in a screening on scope and limitation in the catalytic dehydrative alkylation of anilines by using alcohols.     

Liquid-phase catalytic oxidation of organic substrates by a recyclable polymer-supported copper(II) complex

Chloromethylated polystyrene beads cross-linked with 6.5 % divinylbenzene were functionalized with 2-(2′-pyridyl) benzimidazole (PBIMH) and on subsequent treatment with Cu(OAc)₂ in methanol gave a polymer-supported diacetatobis(2-pyridylbenzimidazole)copper(II) complex [PS-(PBIM)₂Cu(II)], which was characterized by physicochemical techniques. The supported complex showed excellent catalytic activity toward the oxidation of industrially important organic compounds such as phenol, benzyl alcohol, cyclohexanol, styrene, and ethylbenzene. An effective catalytic protocol was developed by varying reaction parameters such as the catalyst and substrate concentrations, reaction time, temperature, and substrate-to-oxidant ratio to obtain maximum selectivity with high yields of products. Possible reaction mechanisms were worked out. The catalyst could be recycled five times without any metal leaching or much loss in activity. This catalyst is truly heterogeneous and allows for easy work up, as well as recyclability and excellent product yields under mild conditions.     

磷钨反应控制相转移催化剂的制备及表征

制备了三缺位Keggin型反应控制相转移催化剂[C7H7(CH3)3N]9PW9O34(记为Q9PW9),利用FT-IR、31P NMR、XRD和TG对催化剂进行了表征,并确定了反应的催化活性中心。 分析结果表明,催化剂Q9PW9在反应后其结构仍然得到了很好的保持,反应中形成的[C7H7(CH3)3N]9PW9O34 (O2)x活性中心使催化剂具有反应控制相转移功能。以H2O2水溶液为氧化剂,在氧化苯甲醇制备苯甲醛反应中,发现该催化剂具有良好的催化活性。当H2O2与苯甲醇的物质的量比为0.9时,苯甲醇的转化率为86.2%,苯甲醛的选择性≥99%。反应结束后催化剂以沉淀的形式析出,催化剂的回收率保持在86%左右。将催化剂循环使用三次,苯甲醇的转化率和催化剂的回收率均无明显变化,说明Q9PW9具有良好的稳定性。     

Synthesis,characterization, fluorescence and redox features of new <Emphasis Type="Italic">vic</Emphasis>-dioxime ligand bearing pyrene and its metal complexes

A new vic-dioxime ligand, N,N′-bis(aminopyreneglyoxime) (LH₂), and its copper(II), nickel(II) and cobalt(II) metal complexes were synthesized and characterized by elemental analyses, IR, UVVIS and ¹H and ¹³C NMR spectra (for the ligand). Mononuclear complexes were synthesized by a reaction of ligand (LH₂) and salts of Co(II), Ni(II), and Cu(II) in ethanol. The complexes have the metal-ligand ratio of 1: 2 and metals are coordinated by N,N′ atoms of vicinal dioximes. The ligand acts in a polydentate fashion bending through nitrogen atoms in the presence of a base, as do most vic-dioximes. Detection of a H-bonding in the Co(II), Ni(II), and Cu(II) complexes by IR revealed the square-planar MN₄ coordination of mononuclear complexes. Fluorescent properties of the ligand and its complexes arise from pyrene units conjugated with a vic-dioxime moiety. Fluorescence emission spectra of the ligand showed a drastic decrease in its fluorescence intensity upon metal binding. The electrochemical properties of the complexes were studied by the cyclic voltammetry technique. The nickel complex displayed an irreversible oxidation process while the copper complex exhibited a quasi-reversible oxidation and reduction processes based on the copper Cu(II)/Cu(III) and Cu(II)/Cu(I) couples, respectively.     

Non-linear correlations between formal potential and Hammett parameters of substituted iron phthalocyanines and catalytic activity for the electro-oxidation of hydrazine

The activity of the different iron phthalocyanines was examined using the complexes adsorbed on graphite electrodes. The effect of the Fe(II)/(I) formal potential of iron phthalocyanines on the their catalytic activity for the electro-oxidation of hydrazine was investigated. A plot of log k (rate constant at constant potential) versus the Fe(II)/(I) formal potential gives a volcano curve. The rate of the reaction increases with the driving force of the catalyst (measured as its formal potential) and then decreases for higher driving forces. A similar graph is obtained with a plot of log k versus the sum of the Hammett parameters of the substituents on the periphery of the phthalocyanine ligand. A maximum activity is obtained for a complexes having an M(II)/(I) redox potential close to –0.6 V which agrees with previous studies conducted with phthalocyanines of different metals and with cobalt phthalocyanines bearing different substituents.Dedicated to Prof. Wolf Vielstich on the occasion of his 80th birthday in recognition of his numerous contributions to interfacial electrochemistry.     

Anthracene Substituted Co (II) and Cu (II) phthalocyanines; Preparations,Investigation of Catalytical and Electrochemical Behaviors

An approach to investigation of catalytical behaviors of Co (II) and Cu (II) phthalocyanines is reported that is based on changing any parameter to effect these behaviors. Towards this end, new anthracene substituted Co (II) and Cu (II) phthalocyanines were prepared and characterized spectroscopic methods. New cobalt (II) and copper (II) phthalocyanines were used as catalyst for oxidation of different phenolic compounds (such as 2,3‐dichlorophenol, 4‐methoxyphenol, 4‐nitrophenol, 2,3,6‐trimethylphenol) with different oxidants. Then, electrochemical characterization of cobalt (II) and copper (II) phthallocyanines were determined by using cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques. Although copper (II) phthalocyanine showed similar Pc based electron transfer processes, cobalt (II) phthalocyanine showed metal and ligand based reduction reactions as expected.     

Studies on the Phenol Oxidation by H2O2 Catalyzed by Metallomicelle Made from Crowned Schiff Base Co(II) Complexes Containing Benzoaza-15-crown-5

Three novel cobalt(II) complexes of the benzoaza-15-crown-5 Schiff base, CoL¹, CoL², and CoL³ were synthesized and characterized. Metallomicelles made from CoL and surfactants (CTAB, LSS, and Brij35) were used as mimetic peroxidase in the catalytic oxidation of phenol by H₂O₂. For comparison, the catalytic activity of the complexes (CoL¹, CoL², and CoL³) were also investigated. The mechanism and a kinetic mathematic model of the phenol catalytic oxidation were studied. The acid effect of reaction system, structural effect of the complexes, and effect of temperature on the rate of the phenol catalytic oxidation by the mimetic peroxidase were discussed. The results show that the Schiff base cobalt(II) complexes and their metallomicelles as peroxidase mimics exhibit good catalytic activity and similar catalytic character to natural enzyme.     

Synthesis,characterization and catalytic properties of novel palladium(II) complexes containing aromatic sulfonamides: effective catalysts for the oxidation of benzyl alcohol

In this article, N‐(2‐aminophenyl)arylsulfonamides (1–5) were successfully synthesized by the reaction of o‐phenylenediamine and various benzenesulfonyl chlorides. The Schiff base derivatives (1a–f; 4e) of those compounds were obtained using different aldehydes. Then, a series of neutral‐four coordinate Pd(II) complexes (6–10) were prepared from the reaction of Pd(OAc)₂ and 1–5. On the other hand, when we tried to synthesize Pd(II) complexes containing Schiff base/sulfonamide ligands, two different situations were observed. Generally, when an electron‐donating group was attached to the imine fragment (1a–d) except for 1f, the Schiff base hydrolyzed and 6 was isolated. When an electron‐withdrawing group was attached to the imine fragment (1e, 4e), neutral four‐coordinate Pd(II) complexes (11–13) bearing Schiff base/sulfonamide ligands were isolated. The synthesized compounds were characterized by FT‐IR, elemental analysis and NMR spectroscopy. The complexes were used as a catalyst in the oxidation reaction of benzyl alcohol to benzaldehyde in the presence of H₅IO₆ in acetonitrile. All complexes showed satisfactory catalytic activity. The highest catalytic activity was obtained with 9. Copyright © 2012 John Wiley & Sons, Ltd.     

Simple synthesis of the novel Cu-MOF catalysts for the selective alcohol oxidation and the oxidative cross-coupling of amines and alcohols

A novel porous metal–organic framework {Cu₂(bbda)_0.5(Hbbda)_1.5(OAc)_1.5.8H₂O} (UoB-5) was synthesized under ultrasound irradiation by employing a new Schiff base ligand H₂bbda (4,4′(1,4-phenylene bis (azanylylidene)) bis (methanylylidene))dibenzoic acid) and was fully characterized. The microporous nature of UoB-5 was confirmed by gas-sorption measurements. This framework acted as a highly effective heterogeneous catalyst for the alcohol oxidation reaction with tert-butyl hydroperoxide (t-BuOOH) as an oxidant. The presence of coordinatively unsaturated metal sites in UoB-5 could be the reason for high performance in this reaction. Furthermore, using the long linker with the free -NC group and uncoordinated -N atom on the wall of the pores created UoB-5 an excellent candidate for the catalytic activities without activation of the framework. It was confirmed with the heterogeneous catalytic experiments on the one-pot tandem synthesis of imines from benzyl alcohols and anilines. Eventually, the new Cu-MOF (UoB-5) could be an alternative catalyst as a more economically favorable and environmentally friendly in the catalysis field.     

Ag/SBA-15低温气相选择性催化氧化苯甲醇合成苯甲醛

以SBA-15为载体,采用浸渍法制备了不同Ag含量的Ag/SBA-15,通过N₂吸附-脱附、X射线衍射、扫描电子显微镜、高分辨透射电子显微镜、X射线光电子能谱和电感耦合等离子体质谱对催化剂进行了表征。将Ag/SBA-15用于苯甲醇气相选择性催化氧化合成苯甲醛,研究了反应条件对转化率和选择性的影响。结果表明,Ag/SBA-15具有均一的一维孔道结构、较厚的孔壁（3-5 nm）及较大的比表面积（411-541 m²/g）,其规整纳米空间的限域作用使一定负载量的Ag以纳米尺寸均匀分散于介孔SBA-15孔道内,增加了活性组分的比表面积。亲核性氧物种从Ag到SBA-15表面的氧溢流,提高了低温下Ag/SBA-15对苯甲醇气相选择性氧化合成苯甲醛的催化性能。5.3% Ag/SBA-15中的Ag粒径为5-6 nm,且均匀分散于载体孔道中,反应温度为220℃时,苯甲醇转化率为87%,苯甲醛选择性为95%;240℃时,苯甲醇转化率和苯甲醛选择性分别高达94%和97%;并在240-300℃范围内,其催化活性和选择性保持不变,表现出了良好的温度耐受能力。催化剂经活化再生可以连续使用40 h,选择性基本保持不变。     

Kinetics of Lab Prepared Manganese Oxide Catalyzed Oxidation of Benzyl Alcohol in the Liquid Phase

The oxidation of benzyl alcohol in the liquid phase was studied over manganese oxide catalyst using molecular oxygen as an oxidant. Manganese oxide was prepared by a mechanochemical process in solid state and was characterized by chemical and physical techniques. The catalytic performance of manganese oxide was explored by carrying out the oxidation of benzyl alcohol at 323–373 K temperature and 34–101 kPa partial pressure of oxygen. Benzaldehyde and benzoic acid were identified as the reaction products. Typical batch reactor kinetic data were obtained and fitted to the Langmuir–Hinshelwood, Eley–Rideal, and Mars–van Krevelene models of heterogeneously catalyzed reactions. The Langmuir–Hinshelwood model was found to give a better fit. Adsorption of benzyl alcohol at the surface of the catalyst followed the Langmuir adsorption isotherm. The heat of adsorption for benzyl alcohol was determined as –18.14 kJ mol^?1. The adsorption of oxygen followed the Temkin adsorption isotherm. The maximum heat of adsorption for oxygen was –31.12 kJ mol^?1. The value of activation energy was 71.18 kJ mol^?1, which was apparently free from the influence of the heat of adsorption of both benzyl alcohol and oxygen.     

Reductive dechlorination of atrazine using sodium-borohydride catalysed by cobalt(II) phthalocyanines

A series of functional metallophthalocyanines have been synthesized to study their role as a catalyst towards the reductive dechlorination of atrazine using sodium borohydride as a mild reducing agent. The cobalt(II) phthalocyanine bearing nitro groups at the peripheral position is the most efficient catalyst with exceptionally high catalytic activity in comparison to other functional cobalt(II) phthalocyanines.     

Theoretical study of the electron transfer reaction of hydrazine with cobalt(II) phthalocyanine and substituted cobalt(II) phthalocyanines

A theoretical model is proposed to explain the trend in reactivity of cobalt(II) phthalocyanine (CoPc) and substituted cobalt(II) phthalocyanines for the oxidation of hydrazine. Our study suggests that the reaction occurs via a through bond charge transfer pathway and not via a through space charge transfer pathway as was shown in previous work for the oxidation of 2-mercaptoethanol by CoPc (G.I. Cárdenas-Jirón and D.A. Venegas-Yazigi, J. Phys. Chem. A. 106, 11398 (2002)). We propose a mechanism for the oxidation of hydrazine based on a four-step energy profile which agrees with a mechanism proposed for the electro-oxidation of hydrazine mediated by cobalt phthalocyanines confined on a graphite electrode. We show that the step in the energy profile that involves formation of a radical of hydrazine seems to be a good starting point for the study of the transfer of the first electron in the oxidation of hydrazine mediated by different substituted cobalt(II) phthalocyanines.