Picolinimidoamide-Cu(II) complex anchored on Fe3O4@SiO2 core–shell magnetic nanoparticles: an efficient reusable catalyst for click reaction

A Cu(II) complex supported on Fe₃O₄@SiO₂ core–shell magnetic nanoparticles (MNPs) was prepared and characterized by FT-IR, XRD, SEM, EDX, TEM, VSM, TGA, and AAS analysis. The load of Cu on picolinimidoamide ligand anchored on Fe₃O₄@SiO₂ core–shell MNPs was determined as 1.22, 1.54, and 1.70 wt% using AAS, EDX and TGA analyses, respectively. Synthesized Cu(II) complex on Fe₃O₄@SiO₂ MNPs efficiently catalyzed a click reaction between alkyl halides, alkynes, and sodium azide to synthesize corresponding triazoles in high to excellent yields. The catalyst was recovered using an external magnetic field, and recycled for subsequent reactions without substantial loss of efficiency.     

Green,cost‐effective and efficient procedure for Heck and Sonogashira coupling reactions using palladium nanoparticles supported on functionalized Fe3O4@SiO2 by polyvinyl alcohol as a highly active,durable and reusable catalyst

A novel heterogenized organometallic catalyst was synthesized by coordinating palladium with polyvinyl alcohol‐functionalized Fe₃O₄@SiO₂ nanospheres. This novel catalyst was characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, transmission electron microscope, field emission scanning electron microscope, dynamic light scattering, UV–vis spectroscopy, X‐ray photoelectron spectroscopy, energy dispersive X‐ray analysis, thermogravimetric analysis and inductively coupled plasma analysis. The prepared palladium nanoparticles supported on polyvinyl alcohol functionalized Fe₃O₄@SiO₂ nanoparticles were successfully applied as a magnetically recyclable catalyst in Heck and Sonogashira coupling reactions in water. They showed remarkable activity toward aryl halides (I, Br, Cl) using very low palladium loading in excellent yields and demonstrated high TONs (mmol of product per mmol of catalyst). Also, the catalyst could be magnetically separated and reused seven times without any appreciable loss of catalytic activity.     

Synthesis,characterization and application of sulfonic acid supported on ferrite–silica superparamagnetic nanoparticles

In this study, the synthesis of sulfonic acid supported on ferrite–silica superparamagnetic nanoparticles (Fe₃O₄@SiO₂@SO₃H) as a nanocatalyst with large density of acidic groups is suggested. This nanocatalyst was prepared in three steps: preparation of colloidal iron oxide magnetic nanoparticles (Fe₃O₄ MNPs), coating of silica on Fe₃O₄ MNPs (Fe₃O₄@SiO₂) and incorporation of sulfonic acid as a functional group on the surface of Fe₃O₄@SiO₂ nanoparticles (Fe₃O₄@SiO₂@SO₃H). The properties of the prepared magnetic nanoparticles were characterized using transmission electron microscopy, infrared spectroscopy, vibrating sample magnetometry, X‐ray diffraction and thermogravimetric analysis. Finally, the applicability of the synthesized magnetic nanoparticles was tested as a heterogeneous solid acid nanocatalyst for one‐pot synthesis of diindolyloxindole derivatives in aqueous medium. Oxindole derivatives were produced by the coupling of indole and isatin compounds with good to high yields (60–98%). Copyright © 2016 John Wiley & Sons, Ltd.     

Preparation of novel palladium nanoparticles supported on magnetic iron oxide and their catalytic application in the synthesis of 2‐imino‐3‐phenyl‐2,3‐dihydrobenzo[d]oxazol‐5‐ols

Novel Pd nanoparticles were prepared in five successive stages: 1) preparation of the Fe₃O₄ magnetic nanoparticles (Fe₃O₄ MNPs), 2) coating of Fe₃O₄ MNPs with SiO₂ (Fe₃O₄@SiO₂), 3) functionalization of Fe₃O₄@SiO₂ with 3‐chloropropyltrimethoxy‐ silane (CPTMS) ligand (Fe₃O₄@SiO₂@CPTMS), 4) further functionalization with 3,5‐diamino‐1,2,4‐triazole (DAT) ligand (Fe₃O₄@SiO₂@CPTMS @DAT), and 5) the complexation of Fe₃O₄@SiO₂@CPTMS@DAT with PdCl₂ (Fe₃O₄@SiO₂@CPTMS@ DAT@Pd). Then, the obtained Pd nano‐catalyst characterized by different methods such as the elemental analysis (CHN), FT‐IR, XRD, EDX, SEM, TEM, TG‐DTA and VSM. Finally, the Pd catalyst was applied for the synthesis of various 2‐imino‐3‐phenyl‐2,3‐dihydrobenzo[d]oxazol‐5‐ols.     

Uniformly dispersed copper nanoparticles onto the modified magnetically recoverable nanocatalyst for aqueous synthesis of primary amides

Magnetically recoverable and environmentally friendly Cu‐based heterogeneous catalyst has been synthesized for the one‐pot conversion of aldehydes to their corresponding primary amides. The Fe₃O₄@SiO₂ nanocomposites were prepared by synthesis of Fe₃O₄ magnetic nanoparticles (MNPs) which was then coated with a silica shell via Stöber method. Bi‐functional cysteine amino acid was covalently bonded onto the siliceous shell of nanocatalyst. The Cu^II ions were then loaded onto the modified surface of nanocatalyst. Finally, uniformly dispersed copper nanoparticles were achieved by reduction of Cu^II ions with NaBH₄. Amidation reaction of aryl halides with electron‐withdrawing or electron‐donating groups and hydroxylamine hydrochloride catalyzed with Fe₃O₄@SiO₂@Cysteine‐copper (FSC‐Cu) MNPs in aqueous condition gave an excellent yield of products. The FSC‐Cu MNPs could be easily isolated from the reaction mixture with an external magnet and reused at least 8 times without significant loss in activity.     

Application of modified magnetic nanoparticles with amine groups as an efficient solid sorbent for simultaneous removal of 2,4-Dichlorophenoxyacetic acid and 2-methyl-4-chlorophenoxyacetic acid from aqueous solution: optimization and modeling

In the present work, functionalized magnetic nano-adsorbent with amine groups (Fe₃O₄@SiO₂@NH₂) was prepared for the simultaneous removal of 2,4-Dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA) from aqueous solution. Characterization such as Fourier transform infrared spectroscopy, vibrating sample magnetometry, and scanning electron microscope confirmed that the magnetic nanoparticles structure of Fe₃O₄@SiO₂ nano-adsorbent was successfully functionalized by amine groups. The impact of some influencing parameters such as contact time, pH, adsorbent dosage, 2,4-D and MCPA initials concentration and solution temperature were studied. The equilibrium data were analyzed by Langmuir and Freundlich adsorption isotherms and also two models kinetically of pseudo-first-order and pseudo-second-order. Findings of the present study showed that the synthesized amino-functionalized MNPs will be helpful in use as an effective recyclable adsorbent for the removal of phenoxy acid herbicides from aqueous solution due to its advantages such as facile and rapid separation of target molecules from solution.     

Butane‐1‐sulfonic acid immobilized on magnetic Fe3O4@SiO2 nanoparticles: A novel and heterogeneous catalyst for the one‐pot synthesis of barbituric acid and pyrano[2,3‐d] pyrimidine derivatives in aqueous media

Butane‐1‐sulfonic acid immobilized on magnetic Fe₃O₄@SiO₂ nanoparticles (Fe₃O₄@SiO₂‐Sultone) was easily prepared via direct ring opening of 1,4‐butanesultone with nanomagnetic Fe₃O₄@SiO₂. The prepared reagent was characterized and used for the efficient promotion of the synthesis of barbituric acid and pyrano[2,3‐d] pyrimidine derivatives. All reactions were performed under mild and completely heterogeneous reaction conditions affording products in good to high yields. The catalyst is easily isolated from the reaction mixture by magnetic decantation and can be reused at least eight times without significant loss in activity.     

Gallic acid grafted to amine‐functionalized magnetic nanoparticles as a proficient catalyst for environmentally friendly synthesis of α‐aminonitriles

An effective approach of one‐pot catalytic Strecker reaction between aromatic aldehydes, aniline or toluidine and trimethylsilyl cyanide in the presence of amine‐functionalized Fe₃O₄@SiO₂ nanoparticles grafted with gallic acid (GA) as a powerful catalyst was developed. The fabricated reusable catalyst demonstrated high efficiency in the synthesis of α‐aminonitriles along with facile work‐up procedure. Fe₃O₄@SiO₂‐NH₂‐GA was characterized by Fourier transform‐infrared spectroscopy, scanning electron microscopy image, vibrating‐sample magnetometer curve, energy‐dispersive X‐ray analysis and thermogravimetric analysis.     

MgBr2 supported on Fe3O4@SiO2 ~ urea nanoparticle: An efficient catalyst for ortho‐formylation of phenols and oxidation of benzylic alcohols

Urea was successfully immobilized on the surface of chloropropyl‐modified Fe₃O₄@SiO₂ core–shell magnetic nanoparticles, then supported by MgBr₂ and acts as a unique catalyst for oxidation of benzylic alcohols to aldehydes and ketones, and ortho‐formylation of phenols to salicylaldehydes. The prepared catalyst was characterized by FT‐IR, transmission electron microscopy, scanning electron microscopy, X‐ray powder diffraction, dispersive X‐ray spectroscopy, CHN and TGA. It was found that Fe₃O₄@SiO₂ ~ urea/MgBr₂ showed higher catalytic activity than homogenous MgBr₂, and could be reused several times without significant loss of activity.     

Sulfonated magnetic nanocatalyst and application for synthesis of novel Spiro[acridine-9,5′-thiazole]-1,4′-dione derivatives

Sulfonated Sulfurol supported Fe₃O₄ (Fe₃O₄@SiO₂-Pr-Sulfurol-SO₃H) a new magnetic reusable nanocatalyst was prepared using chemical modification of magnetic nanoparticles (MNPs) surface with Sulfurol-SO₃H. The Sulfurol-SO₃H moieties on the surface of MNPs act as acidic catalytic sites for catalysis purposes. Fe₃O₄@SiO₂-Pr-Sulfurol-SO₃H was authenticated by usual analytical and spectroscopic techniques. The prepared Fe₃O₄@SiO₂-Pr-Sulfurol-SO₃H MNPs were applied to the preparation of novel Spiro[acridine-9,5′-thiazole]-1,4′-dione derivatives via the three-component condensation of isatins, dimedone and thioamides or thioureas.

     

Synthesis of a highly active amino‐functionalized Fe3O4@SiO2/APTS/Ru magnetic nanocomposite catalyst for hydrogenation reactions

An amino‐functionalized silica‐coated Fe₃O₄ nanocomposite (Fe₃O₄@SiO₂/APTS) was synthesized. The Fe₃O₄@SiO₂ microspheres possessed a well‐defined core–shell structure, uniform sizes and high magnetization. An immobilized ruthenium nanoparticle catalyst (Fe₃O₄@SiO₂/APTS/Ru) was obtained after coordination and reduction of Ru³⁺ on the Fe₃O₄@SiO₂/APTS nanocomposite. The Ru nanoparticles were not only ultra‐small with nearly monodisperse sizes but also had strong affinity with the surface of Fe₃O₄@SiO₂/APTS. The obtained catalyst exhibited excellent catalytic performance for the hydrogenation of a variety of aromatic nitro compounds, even at room temperature. Moreover, Fe₃O₄@SiO₂/APTS/Ru was easily recovered using a magnetic field and directly reused for at least five cycles without significant loss of its activity.     

N‐heterocyclic carbene–palladium(II) complex supported on magnetic mesoporous silica for Heck cross‐coupling reaction

Magnetic mesoporous silica was prepared via embedding magnetite nanoparticles between channels of mesoporous silica (SBA‐15). The prepared composite (Fe₃O₄@SiO₂‐SBA) was then reacted with 3‐chloropropyltriethoxysilane, sodium imidazolide and 2‐bromopyridine to give 3‐(pyridin‐2‐yl)‐1H‐imidazol‐3‐iumpropyl‐functionalized Fe₃O₄@SiO₂‐SBA as a supported pincer ligand for Pd(II). The functionalized magnetic mesoporous silica was further reacted with [PdCl₂(SMe₂)₂] to produce a supported N‐heterocyclic carbene–Pd(II) complex. The obtained catalyst was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, energy‐dispersive X‐ray analysis, vibrating sample magnetometry, Brunauer–Emmett–Teller surface area measurement and X‐ray diffraction. The amount of the loaded complex was 80.3 mg g^?1, as calculated through thermogravimetric analysis. The formation of the ordered mesoporous structure of SBA‐15 was confirmed using low‐angle X‐ray diffraction and transmission electron microscopy. Also, X‐ray photoelectron spectroscopy confirmed the presence of the Pd(II) complex on the magnetic support. The prepared magnetic catalyst was then effectively used in the coupling reaction of olefins with aryl halides, i.e. the Heck reaction, in the presence of a base. The reaction parameters, such as solvent, base, temperature, amount of catalyst and reactant ratio, were optimized by choosing the coupling reaction of 1‐bromonaphthalene and styrene as a model Heck reaction. N‐Methylpyrrolidone as solvent, 0.25 mol% catalyst, K₂CO₃ as base, reaction temperature of 120°C and ultrasonication of the catalyst for 10 min before use provided the best conditions for the Heck cross‐coupling reaction. The best results were observed for aryl bromides and iodides while aryl chlorides were found to be less reactive. The catalyst exhibited noticeable stability and reusability.     

聚乙烯基胺包裹Fe3O4@SiO2磁性微球用于Knoevenagel缩合（英文）简

Polyvinyl amine coated Fe₃O₄@SiO₂ composite microspheres with a core-shell structure were prepared and employed as a magnetic catalyst for Knoevenagel condensation under mild conditions. The catalyst can be readily recovered using a magnet and reused several times without loss in activity or selectivity. The performance of the magnetic base catalyst was compared with that of polyvinyl amine functionalized mesoporous SBA-15, which showed that the magnetic nanoparticles gave improved reaction rate and yield.     

Novel CuFe2O4@SiO2‐OP2O5H magnetic nanoparticles: Preparation,characterization and first catalytic application to the synthesis of 1,8‐dioxo‐octahydroxanthenes

New functionalized magnetic core–shell nanoparticles, CuFe₂O₄@SiO₂‐OP₂O₅H, were prepared by grafting of phosphorus pentoxide on CuFe₂O₄@SiO₂ nanoparticles and characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, energy‐dispersive X‐ray analysis, inductively coupled plasma optical emission spectrometry and vibrating sample magnetometry. The catalytic activity of CuFe₂O₄@SiO₂‐OP₂O₅H as a novel catalyst was evaluated in the synthesis of 1,8‐dioxo‐octahydroxanthenes under solvent‐free conditions. The results showed that the catalyst has high activity and the desired products are obtained in high yields within short reaction times. The catalyst is readily recovered using magnetic decantation and can be used at least four times without noticeable deterioration in catalytic activity.     

Diazabicyclo[2.2.2]octane stabilized on Fe3O4 as catalysts for synthesis of coumarin under solvent-free conditions

Fe₃O₄-diazabicyclo[2.2.2]octane (Fe₃O₄-DABCO) magnetic nanoparticles (MNPs) catalyst was readily prepared from inexpensive starting materials in aqueous media which catalyzed the synthesis of coumarin. FTIR spectroscopy, X-ray diffraction, transmission electron micrographs were employed to characterize the properties of the synthesized Fe₃O₄-DABCO MNPs. 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.     

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     

Functionalization of superparamagnetic Fe3O4@SiO2 nanoparticles with a Cu(II) binuclear Schiff base complex as an efficient and reusable nanomagnetic catalyst for N‐arylation of α‐amino acids and nitrogen‐containing heterocycles with aryl halides

Fe₃O₄@SiO₂ nanoparticles was functionalized with a binuclear Schiff base Cu(II)‐complex (Fe₃O₄@SiO₂/Schiff base‐Cu(II) NPs) and used as an effective magnetic hetereogeneous nanocatalyst for the N‐arylation of α‐amino acids and nitrogen‐containig heterocycles. The catalyst, Fe₃O₄@SiO₂/Schiff base‐Cu(II) NPs, was characterized by Fourier transform infrared (FTIR) and ultraviolet‐visible (UV‐vis) analyses step by step. Size, morphology, and size distribution of the nanocatalyst were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and dynamic light scatterings (DLS) analyses, respectively. The structure of Fe₃O₄ nanoparticles was checked by X‐ray diffraction (XRD) technique. Furthermore, the magnetic properties of the nanocatalyst were investigated by vibrating sample magnetometer (VSM) analysis. Loading content as well as leaching amounts of copper supported by the catalyst was measured by inductive coupled plasma (ICP) analysis. Also, thermal studies of the nanocatalyst was studied by thermal gravimetric analysis (TGA) instrument. X‐ray photoelectron spectroscopy (XPS) analysis of the catalyst revealed that the copper sites are in +2 oxidation state. The Fe₃O₄@SiO₂/Schiff base‐Cu(II) complex was found to be an effective catalyst for C–N cross‐coupling reactions, which high to excellent yields were achieved for α‐amino acids as well as N‐hetereocyclic compounds. Easy recoverability of the catalyst by an external magnet, reusability up to eight runs without significant loss of activity, and its well stability during the reaction are among the other highlights of this catalyst.     

An Fe3O4 nanoparticle-supported Mn (II)-azo Schiff complex acts as a heterogeneous catalyst in alcoholysis of epoxides

In this paper, an azo-containing Schiff base complex of manganese [Mn²⁺-azo ligand@APTES-SiO₂@Fe₃O₄] immobilized on chemically modified Fe₃O₄ nanoparticles has been used as a magnetically retrievable catalyst for the alcoholysis of different epoxides to their corresponding alkoxy alcohols with methanol, ethanol and n-propanol. The newly magnetic nanoparticles (MNPs) were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and vibrating sample magnetometry (VSM).     

Fe3O4@SiO2–ZrCl2‐MNPs: A novel magnetic catalyst for the clean and efficient cascade synthesis of 1‐(benzothiazolylamino)methyl‐2‐naphthol derivatives in the absence of solvent

A green, simple and eco‐friendly three‐component condensation for the synthesis of 1‐(benzothiazolylamino)methyl‐2‐naphthols using new magnetic nanoparticles formulated as Fe₃O₄@SiO₂–ZrCl₂‐MNPs is described. Considering the economic and environmental aspects, the method provides some advantages such as clean procedure, solvent‐free conditions, simple operation and work‐up, relatively short reaction times and high yields of the products. Moreover the introduced catalyst can be readily recovered up to 4 consecutive runs with consistent activity using an external magnet.     

Preparation of novel magnetic fluorescent microspheres from copperas and fluorescence enhancement with zinc ions

The aim of this study is to develop a new method for the preparation of Fe₃O₄@SiO₂–An NPs from copperas. The core–shell structures of the nanoparticles and chemical composition have been confirmed by TEM, XRD and FTIR techniques. Fluorescence Enhancement of Fe₃O₄@SiO₂–An NPs with zinc ions was investigated by fluorescence emission spectra. The results indicated that the Fe₃O₄ NPs with a high purity (Total Fe 72.16 %) were obtained from copperas by chemical co-precipitation method and have a uniform spherical morphology with an average diameter of about 10 nm. The Fe₃O₄ NPs coated with silica nanoparticles were prepared, and an attempt had been made that the Fe₃O₄@SiO₂ NPs were modified by 3-aminopropyltriethoxysilane and 9-anthranone successively. The recommended mole ratio of ethanol to water and the content of ammonia water added were 4:1 and 25 wt% respectively, which have an obviously effect on the combination of the final well-ordered MNPs with the amino functionalities and reactant components. The functionalized Fe₃O₄@SiO₂–An NPs have a fluorescence property and this fluorescence effect can be enhanced with the Zn²⁺ ions attachment. Meanwhile, the saturated magnetization of Fe₃O₄@SiO₂–An NPs was 37.8 emug^?1 at 25 °C and this fluorescent material exhibited excellent magnetic properties. A new way was therefore provided for the comprehensive utilization of the unmarketable copperas. Moreover, the functionalized Fe₃O₄@SiO₂–An NPs have a big potential in environmental decontamination, medical technology and biological science.