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     

空心结构磁性固体碱催化剂Fe3O4@LDO的制备与性能

基于水滑石类化合物的复合氧化物(LDO)是一类性能优异的固体碱催化剂,对其进行改性和功能化引起了越来越多的关注。本文将空心结构和Fe_3O_4引入到镁铝复合氧化物中,制备了一种空心结构磁性固体碱催化剂Fe_3O_4@LDO。这种空心结构磁性固体碱催化剂粒子具有以镁铝复合氧化物为壳层,空心Fe_3O_4为核的核壳结构。由于其独特的空心结构,Fe_3O_4@LDO粒子的悬浊液具有良好的稳定性,将其应用于催化Knoevenagel缩合反应,达到平衡后苯甲醛的转化率约为62%,显示出较好的催化性能。同时,Fe_3O_4@LDO粒子具有较强的磁性,非常方便分离与回收,是一种性能优良的磁性固体碱催化剂。     

磁性纳米Pd/Fe3O4催化剂的制备及其在Heck反应中的应用

通过使用聚乙烯吡咯烷酮作为稳定剂,合成了磁性Pd/Fe₃O₄纳米颗粒催化剂。对该催化剂进行粉末X射线衍射、透射电子显微镜、感应耦合等离子体和磁性表征。将Pd/Fe₃O₄催化剂用于Heck反应,检测其催化性能。测试结果表明Pd纳米颗粒负载在Fe₃O₄纳米颗粒上,而且催化剂的尺寸<20 nm,并在Heck反应中表现了极好的催化性能。此外,催化剂可以通过磁场回收利用, 且催化活性没有显著的降低。     

Heterogeneous gold(I)-catalyzed three-component reaction of aldehydes,alkynes, and orthoformates toward propargyl ethers

Abstract

A novel and efficient heterogeneous gold(I)-catalyzed three-component reaction of aldehydes, alkynes, and orthoformates has been developed that proceeds smoothly in dichloroethane (DCE) at 83?°C in the presence of 5?mol% magnetic nanoparticles-anchored phosphine gold(I) complex (Fe₃O₄@SiO₂-P-AuOTf) and offers a general and practical approach for the preparation of a variety of propargyl ethers with good yields. This heterogeneous gold(I) catalyst can be facilely recovered by simply applying an external magnetic field and recycled at least eight times without any apparent decrease in the catalytic efficiency.     

Encapsulation of Pd(II) into superparamagnetic nanoparticles grafted with EDTA and their catalytic activity towards reduction of nitroarenes and Suzuki–Miyaura coupling

A robust, safe and magnetically recoverable palladium catalyst was synthesized by anchoring Pd(II) onto ethylenediaminetetraacetic acid‐coated Fe₃O₄ (Fe₃O₄@EDTA) magnetic nanoparticles. The Fe₃O₄ magnetic nanoparticle‐supported Pd(II)–EDTA complex catalyst thus obtained was characterized using scanning and transmission electron microscopies, thermogravimetric analysis, vibrating sample magnetometry, X‐ray diffraction, and inductively coupled plasma atomic emission and Fourier transform infrared spectroscopies. Fe₃O₄@EDTA–Pd(II) was screened for the Suzuki reaction and reduction of nitro compounds in water. The Pd content of the catalyst was measured to be 0.28 mmol Pd g^?1. In addition, the Fe₃O₄@EDTA–Pd catalyst can be easily separated and recovered with an external permanent magnet. The anchored solid catalyst can be recycled efficiently and reused five times with only a very slight loss of catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Copper(I)–creatine complex on magnetic nanoparticles as a green catalyst for N- and O-arylation in deep eutectic solvent

Immobilization of copper(I) ions on magnetic nanoparticles was performed using surface modification of Fe₃O₄ with creatine. Fe₃O₄@creatine-Cu(I) magnetic catalyst was synthesized and applied in C&bond;X cross-coupling reactions with aryl halides in a deep eutectic as a green solvent. The results indicate the Fe₃O₄@creatine-Cu(I) magnetic nanoparticles showed excellent activity and high stability. In addition, it was revealed that this catalyst can be recycled five times without significant loss in catalytic activity.     

Triton X-100 functionalized Cu(II) dihydrazone based complex immobilized on Fe3O4@dopa: A highly efficient catalyst for oxidation of alcohols,alkanes, and sulfides and epoxidation of alkenes

Here, we have presented a protocol for green synthesis, characterization, and catalytic application of TX100/Fe₃O₄@dopa@CuL ( FDCTX ) magnetically separable nanoparticles. Fe₃O₄@dopa@CuL ( FDC ) was synthesized using a four-step procedure: (i) synthesis of a dihydrazone derivative, (ii) reaction of the dihydrazone derivative with copper perchlorate salt to generate a copper complex of the dihydrazone derivative, (iii) immobilization of the complex onto Fe₃O₄@dopa to generate FDC , and (iv) coating of FDC with surfactant Triton X-100. The as-synthesized homogeneous complex was well characterized using UV–Vis., Fourier-transform infrared (FT-IR), electrospray ionization–mass spectrometry, and single-crystalX-ray techniques. Single-crystalX-ray analysis revealed the tetranuclear framework of the complex. The heterogeneous nanoparticles ( FDCTX ) were characterized using FT-IR, powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersiveX-ray spectroscopy, magnetic hysteresis, and dynamic light scattering techniques. Finally, both the homogeneous and heterogeneous catalysts were utilized for efficient oxidation of alcohols, alkanes, and sulfides and epoxidation of alkenes. A most probable mechanism for the oxidation reaction is proposed at the end of the article.     

Selective Oxidation of Ethane to Acetic Acid Catalyzed by a C-Scorpionate Iron(II) Complex: A Homogeneous vs. Heterogeneous Comparison

The direct, one-pot oxidation of ethane to acetic acid was, for the first time, performed using a C-scorpionate complex anchored onto a magnetic core-shell support, the Fe₃O₄/TiO₂/[FeCl₂{κ³-HC(pz)₃}] composite. This catalytic system, where the magnetic catalyst is easily recovered and reused, is highly selective to the acetic acid synthesis. The performed green metrics calculations highlight the “greeness” of the new ethane oxidation procedure.     

Synthesis,characterization and catalytic performance of core‐shell structure magnetic Fe3O4/P(GMA‐EGDMA)‐NH2/HPG‐COOH‐Pd catalyst

A strategy has been developed for the synthesis, characterization and catalysis of magnetic Fe₃O₄/P(GMA‐EGDMA)‐NH₂/HPG‐COOH‐Pd core‐shell structure supported catalyst. The P(GMA‐EGDMA) polymer layer was coated on the surface of hollow magnetic Fe₃O₄ microspheres through the effect of KH570. The core‐shell magnetic Fe₃O₄/P(GMA‐EGDMA) modified by ‐NH₂ could be grafted with HPG. Then, the hyperbranched glycidyl (HPG) with terminal ‐OH were modified by ‐COOH and adsorbed Pd nanoparticles. The hyperbranched polymer layer not only protected the Fe₃O₄ magnetic core from acid–base substrate corrosion, but also provided a number of functional groups as binding sites for Pd nanoparticles. The prepared catalyst was characterized by UV–vis, TEM, SEM, FTIR, TGA, ICP‐OES, BET, XRD, DLS and VSM. The catalytic tests showed that the magnetic Fe₃O₄/P(GMA‐EGDMA)‐NH₂/HPG‐COOH‐Pd catalyst had excellent catalytic performance and retained 86% catalytic efficiency after 8 consecutive cycles.     

3-Amino-5-mercapto-1,2,4-triazole-functionalized Fe3O4 magnetic nanocomposite as a green and efficient catalyst for synthesis of bis(indolyl)methane derivatives

A core–shell Fe₃O₄@silica magnetic nanocomposite functionalized with 3-amino-5-mercapto-1,2,4-triazole (Fe₃O₄/SiO₂/PTS/AMTA) was prepared using Fe₃O₄ with silica layer, and its surface was modified with 3-amino-5-mercapto-1,2,4-triazole. The novel synthesized magnetite nanocomposite was characterized using various techniques. The catalytic activity of Fe₃O₄/SiO₂/PTS/AMTA was demonstrated in the synthesis of bis(indolyl)methane derivatives under solvent-free conditions. Some of the bis(indolyl)methane derivatives were synthesized through one-pot, three-component reaction of 1 mol of various benzaldehydes or ketones with 2 mol of indole in the presence of Fe₃O₄/SiO₂/PTS/AMTA in good to excellent isolated yields. In addition, the catalyst could be recovered and used for several reaction runs without loss of catalytic activity. The stability of recycled catalyst was investigated. This method has some advantages including experimental simplicity, good to excellent yields, solvent-free conditions and stability and reusability of the catalyst.     

Designing of a magnetically separable Fe3O4@dopa@ML nano-catalyst for multiple organic transformations (epoxidation,reduction, and coupling) in aqueous medium

A copper(II) macrocyclic Schiff base complex (ML) was synthesized by condensation between 2,2-dimethylpropane-1,3-diammine and 2,6-diformyl-4-butylphenol with the aim to modify the surface of widely used magnetically separable nanocatalyst Fe₃O₄@dopa. ML was characterized by physicochemical techniques and single crystal X-ray diffraction. The newly synthesized heterogeneous catalyst Fe₃O₄@dopa@ML was characterized by SEM, TEM, PXRD, EDX, TGA, etc. ML showed stability in aqueous medium and utilizing this unique property, the heterogeneous catalyst Fe₃O₄@dopa@ML was used for catalyzing epoxidation, nitroarene reduction and C–C coupling (Henry reaction) in aqueous medium. The separation method of the prepared nano-catalyst is very easy and can be done with an external magnetic field. The experimental findings suggest that Fe₃O₄@dopa@ML is a versatile “green catalyst.”     

Assembly immobilized palladium(0) on carboxymethylcellulose/Fe3O4 hybrid: An efficient tailor‐made magnetically catalyst for the Suzuki–Miyaura couplings

The Pd nanoparticles (Pd NPs) embedded on magnetically retrievable carboxymethylcellulose/Fe₃O₄ (Pd⁰@CMC/Fe₃O₄) organic/inorganic hybrid were prepared via the conventional simple process. The presence of the hydroxyl and carboxyl groups within the framework of the magnetic hybrid enables the facile preparation and stabilization of Pd NPs in this organic/inorganic hybrid. This hybrid catalyst was very effective in the Suzuki – Miyaura reaction of a variety of aryl halides with arylboronic acid to afford excellent product yields. The catalyst showed good stability and could be easily recovered with an external magnetic field and reused for several times without a significant loss in its catalytic activity. Furthermore, the Pd⁰@CMC/Fe₃O₄ hybrid catalyst was fully characterized by UV–Vis, FT–IR, XRD, SEM, EDX, TEM, XPS and TGA techniques. The hot filtration test suggests that a homogeneous mechanism is operative in Suzuki – Miyaura reaction.     

Copper-based Schiff Base Complex Immobilized on Core-shell Fe3O4@SiO2 as a magnetically recyclable and highly efficient nanocatalyst for green synthesis of 2-amino-4H-chromene derivatives

Fe₃O₄-supported copper (II) Schiff-Base complex has been synthesized through post-modification with 1,3-phenylenediamine followed by further post-modification with salicylaldehyde and coordination with Cu(II) ion. The resulted Fe₃O₄@SiO₂-imine/phenoxy-Cu(II) magnetic nanoparticles (MNPs) were characterized by various techniques including SEM, TEM, XRD, XPS, EDX, VSM, FT-IR, and ICP. The catalytic activity as a magnetically recyclable heterogeneous catalyst for one-pot, three-component synthesis of 2-amino-4H-chromene derivatives was examined. The catalyst is efficient in the reaction and can be recovered by magnetic separation and recycled several times without significant loss in the catalytic activity.     

Manganese(III) Salen Complex Immobilized on Fe3O4 Magnetic Nanoparticles: The Efficient,Green and Reusable Nanocatalyst

A new Fe₃O₄ magnetic nanoparticles supported manganese salen complex was successfully prepared by attaching manganese acetates to a novel N,N′‐bis(salicylidine)ethylenediamine ligand functionalized Fe₃O₄. The as‐prepared catalyst was characterized by TGA, XRD, FTIR, VSM, and TEM. It was found to be an efficient catalyst for the synthesis of benzopyranopyrimidines in aqueous medium. High catalytic activity and ease of recovery from the reaction mixture using external magnet, and several reuse times without significant losses in performance are additional eco‐friendly attributes of this catalytic system.     

Mn(III) complex supported on Fe3O4 nanoparticles: magnetically separable nanocatalyst for selective oxidation of thiols to disulfides

A manganese(III) complex, [Mn(phox)₂(CH₃OH)₂]ClO₄ (phox?=?2-(2′-hydroxyphenyl)oxazoline), was immobilized on silica-coated magnetic Fe₃O₄ nanoparticles through the amino propyl linkage using a grafting process in dichloromethane. The resulting Fe₃O₄@SiO₂–NH₂@Mn(III) nanoparticles are used as efficient and recyclable catalysts for selective oxidation of thiols to disulfides using urea-hydrogen peroxide as the oxidant. The nanocatalyst was recycled several times. Leaching and recycling experiments revealed that the nanocatalyst can be recovered, recycled, and reused more than five times, without the loss of catalytic activity and magnetic properties. The recycling of the nanocatalyst in six consecutive runs afforded a total turnover number of more than 10,000. The heterogeneous Fe₃O₄@SiO₂–NH₂@Mn(III) nanoparticle shows more selectivity for the formation of disulfides in comparison with the homogeneous manganese complex.     

Ni(II)‐Adenine complex coated Fe3O4 nanoparticles as high reusable nanocatalyst for the synthesis of polyhydroquinoline derivatives and oxidation reactions

In the present study, Fe₃O₄ nanoparticles were prepared via simple and versatile procedure. Then, a novel and green catalyst was synthesized by the immobilization of Ni on Fe₃O₄ nanoparticles coated with adenine. The activity of this nanostructure compound was examined for the oxidation of sulfides, oxidative coupling of thiols and synthesis of polyhydroquinolines. The prepared catalyst was characterized by Fourier transform infrared spectroscopy (FT‐IR), scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDS), inductively coupled plasma optical emission spectroscopy (ICP‐OES), X‐ray Diffraction (XRD), thermal gravimetric analysis (TGA), and vibrating sample magnetometer (VSM) measurements. This organometallic catalyst was recovered by the assistance of an external magnetic field from the reaction mixture and reused for seven continuous cycles without noticeable change in its catalytic activity.     

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.     

Synthesis and characterization of a new nanomagnetic coordination composite from Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> and Cu(II) complex: as an efficient catalyst in oxidation of benzyl alcohol

New nanomagnetic coordination compound, Cu(salal)@DA@ Fe₃O₄, was synthesized by bonding between the Cu(II) complex and Fe₃O₄ nanoparticles. The Cu complex has two aldehyde groups. The surface of Fe₃O₄ nanoparticles was modified by the dopamine molecules and the amine group of dopamine is free. Therefore, the Cu complex is covalently anchored to Fe₃O₄ nanoparticle by the formation of imine bonds between the aldehyde and amine groups. On the other hand, a Cu-Schiff base complex is immobilized on nano-Fe₃O₄ by dopamine as a bridge. Consequently, the homogeneous Cu complex is easily converted to the heterogeneous-magnetic compound in this project. The Cu complex, Fe₃O₄ and new nanocomposite were characterized by general techniques such as FTIR, TGA, XRD, FESEM, MAP and EDS. The average crystallite size of Fe₃O₄ and Cu(salal)@DA@ Fe₃O₄ were calculated by Scherrer’s formula and they are 18.52 and 24.69 nm, respectively. These results indicated the average crystallite size of Fe₃O₄ nanomaterials is slightly increased by surface modification by Cu complex. The FESEM images show a tiny spherical mushroom morphology for both nanocompounds, and the EDS analysis confirms the presence of Fe, Cu, C and O in the nanomagnetic coordination composite. The catalytic properties of these compounds were studied and compared to oxidation of benzyl alcohol by 30% H₂O₂ at room temperature. The results show that the catalytic properties Cu complex and Fe₃O₄ were enhanced by cooperation of both compounds in a nanocoordination composite.     

Cu(II)–Schiff base complex‐functionalized magnetic Fe3O4 nanoparticles: a heterogeneous catalyst for various oxidation reactions

Cu(II)–Schiff base complex‐functionalized magnetic Fe₃O₄ nanoparticles were prepared and characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy techniques. This compound acts as a highly active and selective catalyst for the oxidation of sulfides and thiols. These reactions can be carried out in ethanol or solvent‐free conditions in the presence of hydrogen peroxide with complete selectivity and very high conversion under mild reaction conditions. The designed catalytic system prevents effectively the over‐oxidation of sulfides to sulfones. Separation and recycling can also be easily done using a simple magnetic separation process. Copyright © 2015 John Wiley & Sons, Ltd.     

Highly efficient oxidative cleavage of alkenes and cyanosilylation of aldehydes catalysed by magnetically recoverable MIL‐101

The catalytic activity of magnetically recoverable MIL‐101 was investigated in the oxidation of alkenes to carboxylic acids and cyanosilylation of aldehydes. MIL‐101 was treated with Fe₃O₄ and the prepared catalyst was characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, N₂ adsorption measurements, field emission scanning electron microscopy, energy‐dispersive X‐ray spectroscopy and inductively coupled plasma analysis. The catalytic active sites in this heterogeneous catalyst are Cr³⁺ nodes of the MIL‐101 framework. This heterogeneous catalyst has the advantages of excellent yields, short reaction times and reusability several times without significant decrease in its initial activity and stability in both oxidation and cyanosilylation reactions. Its magnetic property allows its easy separation using an external magnetic field.