Synthesis of N-aryl imidazoles catalyzed by copper nanoparticles on nanosized silica-coated maghemite

A magnetically recoverable catalyst consisting of copper nanoparticles (CuNPs) on nanosized silica-coated maghemite is presented. The catalyst has been prepared under mild conditions by mixing the magnetic support with a freshly prepared suspension of CuNPs obtained by fast reduction of anhydrous CuCl₂ with lithium sand and a catalytic amount of DTBB (4,4′-di-tert-butylbiphenyl) as electron carrier. This copper-based catalyst has shown to be very efficient in the N-(hetero)arylation of imidazole using (hetero)aryl bromides and iodides as arylating agents under ligand-free conditions. The catalyst is easily recovered by means of an external magnet and can be reutilized in three N-arylation cycles without apparent loss of catalytic activity.     

Magnetically recoverable γ-Fe2O3 nanoparticles as a highly active catalyst for Friedel–Crafts benzoylation reaction under ultrasound irradiation

A simple, facile and efficient method has been developed for the Friedel–Crafts benzoylation of arenes using magnetic γ-Fe₂O₃ nanoparticles under solvent-free sonication. The γ-Fe₂O₃ nanoparticles were used as an efficient and magnetically recoverable catalyst for the synthesis of aromatic ketones in good to excellent yields at room temperature under solvent-free. The reaction occurred with high regioselectivity under mild condition. The magnetic γ-Fe₂O₃ nanoparticles are economically synthesized in large-scale, easily separated from the reaction mixture by an external magnet and able to be reused several times without significant loss of the catalytic performance, which make them easy application to industrial processes.     

Magnetically modified nanogold-biosilica composite as an effective catalyst for CO oxidation

The temperature-dependent biosynthesis of gold nanoparticles (AuNP) using diatom cells of Diadesmis gallica was successfully performed. The resulting biosynthesis product was a bionanocomposite containing AuNP (app. 20 nm) subsequently anchored on the silica surface of diatomaceous frustules. As-prepared nanogold-biosilica composite was tested as catalyst in the oxidation of carbon monoxide using gas chromatograph with thermal conductivity detector. For catalytic activity enhancement, bionanocomposite was magnetically modified by ferrofluid using two different methods, i.e., with and without the use of methanol. The oxidation of CO at 300 °C was 58–60% in the presence of nanogold-biosilica composites. CO conversion at 300 °C was only 15% over magnetically responsive sample modified in the presence of methanol. On the other hand, complete CO conversion was reached over direct (without methanol) magnetically modified nanogold-biosilica composite at 330 °C (GHSV = 60 l g⁻¹ h⁻¹). Our results show, that the type of magnetic modification can influence the catalytic activity of bionanocomposite. The best catalytic effect in CO conversion established direct magnetically modified nanogold-biosilica composite.     

Magnetic carbon nanotube as a highly stable support for the heterogenization of InCl3 and its application in the synthesis of isochromeno[4,3-c]pyrazole-5(1H)-one derivatives

In the present study, a novel magnetically retrievable catalytic system involving indium nanoparticles on magnetic carbon nanotube (Fe₃O₄-CNT-In) was synthesized and characterized using various techniques, such as Fourier transform-infrared, thermogravimetric analysis, energy-dispersive X-ray analysis, vibrating-sample magnetometry1, X-ray diffraction, field emission-scanning electron microscopy and inductively coupled plasma-optical emission spectrometry. The catalytic activity of the synthesized nanocatalyst was evaluated in green synthesis of isochromeno[4,3-c]pyrazole-5(1H)-one derivatives from the reaction of ninhydrin and arylhydrazones under solvent-free conditions. The catalyst was magnetically separated from the reaction mixture using an external magnet and recovered for five cycles without an appreciable decrease in its catalytic efficiency. Performing the reactions in environmentally friendly and affordable conditions, the low catalyst percentage, high yield of products, short reaction times, large substrate scope and easy work-up are the merits of this protocol. Furthermore, four of the synthesized isochromeno[4,3-c]pyrazole-5(1H)-one derivatives are also new.     

N‐(3‐silyl propyl) diethylene triamine N,N',N'‐tri‐sulfonic acid immobilized on Fe3‐xTixO4 magnetic nanoparticles: A new recyclable heterogeneous nanocatalyst for the synthesis of hexahydroquinolines

In the present study, for the first time N‐(3‐silyl propyl) diethylene triamine N,N',N''‐tri‐sulfonic acid (SPDETATSA) was grafted on magnetic Fe_3‐xTi_xO₄ nanoparticles. The structure of the resulted nanoparticles was characterized based on Fourier‐transform infrared (FT‐IR), energy‐dispersive X‐ray spectroscopy (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), and vibrating sample magnetometer (VSM) analyses. The results confirmed the successful immobilization of sulfamic acid groups onto the magnetic support. These nanoparticles exhibited high catalytic activity as novel magnetically recyclable acid nanocatalyst in the synthesis of a diverse range of hexahydroquinolines through one‐pot tandem reactions in excellent yields. Also, this nanocatalyst performed satisfactory catalytic maintenance of activity for the synthesis of the reaction products after 4 rounds of recycling with no considerable loss of activity.     

CuFe2O4 nanoparticles: a magnetically recoverable and reusable catalyst for the synthesis of 5-substituted 1H-tetrazoles

An efficient and economical protocol for the synthesis of 5-substituted 1H-tetrazoles from various nitriles and sodium azide is described using magnetically recoverable and reusable CuFe₂O₄ nanoparticles. A wide variety of aryl nitriles underwent [2+3] cycloaddition under mild reaction conditions to afford tetrazoles in good to excellent yields. The catalyst was magnetically separated and reused five times without significant loss of catalytic activity.     

Magnetically separable palladium–graphene nanocomposite as heterogeneous catalyst for the synthesis of 2-alkylquinolines via one pot reaction of anilines with alkenyl ethers

The present Letter describes the use of magnetically separable palladium–graphene nanocomposite, a complete magnetically separable catalyst for the synthesis of 2-alkyl quinolines via reaction of anilines with alkenyl ethers. Because of the uniform decoration of the Pd nanoparticles on support, the catalyst exhibited higher catalytic efficiency and it remains unaltered even after six repeated cycles.     

Synthesis and characterization of bromine source supported on magnetic Fe3O4 nanoparticles: A new,versatile and efficient magnetically separable catalyst for organic synthesis

Tribenzylammonium tribromide supported onto magnetic nanoparticles (Br₃‐TBA‐Fe₃O₄) as a bromine source was successfully synthesized and characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy and vibrating sample magnetometry. The synthesized catalyst is shown to be a versatile and highly efficient heterogeneous catalyst for the Knoevenagel condensation and synthesis of 2,3‐dihydroquinazolin‐4(1H )‐one and polyhydroquinoline derivatives. To the best of the authors' knowledge, this is the first report of the use of a bromine source immobilized on Fe₃O₄ nanoparticles as a magnetically separable catalyst for these reactions. The nanosolid catalyst can be magnetically recovered and reused readily several times without significant loss in catalytic efficiency.     

Silica iminopyridine-functionalized nanomaghemite enhances the oxygenation activity and durability of simple Co(II) salophen complex

A novel magnetically recoverable catalyst was produced by coordinative attachment of Co(II) salophen complex to silica iminopyridine (SIPy)-functionalized-γ-Fe₂O₃ magnetic nanoparticles (SMNP@SIPy/Co(II) salophen). The vibration spectra and compositional data provided sufficient evidences for the structural integrity of as-prepared organic–inorganic nanohybrid. The magnetic nanocatalyst proved to be an efficient and selective heterogeneous catalyst for oxidation of different benzylic alcohols and featured higher catalytic activity and stability than that of homogenous counterpart. A TOF of 151 h⁻¹ and TON of more than 322 were obtained for oxidation of 4-cholrobenzyl alcohol in this catalytic system. The supported catalyst could easily be recovered from the reaction mixture by an external magnetic field and reused for subsequent experiments with consistent catalytic activity.     

Sulfamic acid heterogenized on functionalized magnetic Fe3O4 nanoparticles with diaminoglyoxime as a green,efficient and reusable catalyst for one‐pot synthesis of substituted pyrroles in aqueous phase

Surface functionalization of magnetic nanoparticles is an elegant way to bridge the gap between heterogeneous and homogeneous catalysis. We have conveniently loaded sulfonic acid groups on amino‐functionalized Fe₃O₄ nanoparticles affording sulfamic acid‐functionalized magnetic Fe₃O₄ nanoparticles (MNPs/DAG‐SO₃H) as an active and stable magnetically separable acidic nanocatalyst, which was characterized using X‐ray diffraction, Fourier transform infrared and energy‐dispersive X‐ray spectroscopies, scanning and transmission electron microscopies, vibrating sample magnetometry and elemental analysis. The catalytic activity of MNPs/DAG‐SO₃H was probed through one‐pot synthesis of N‐substituted pyrroles from γ‐diketones and primary amines in aqueous phase at room temperature. The heterogeneous catalyst could be recovered easily by applying an external magnet device and reused many times without significant loss of its catalytic activity. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and characterization of sulfamic acid supported on Fe3O4 nanoparticles: A green,versatile and magnetically separable acidic catalyst for oxidation reactions and Knoevenagel condensation

Sulfamic acid immobilized on diethylenetriamine functionalized Fe₃O₄ nanoparticles (SA‐DETA‐Fe₃O₄) was successfully prepared and characterized by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR), vibrating sample magnetometer (VSM), thermo gravimetric analysis (TGA), X‐Ray diffraction (XRD) and scanning electron microscopy (SEM). The sulfamic acid was found as a magnetically separable and highly active catalyst for the oxidative coupling thiols, oxidation of sulfides. Furthermore, the SA‐DETA‐Fe₃O₄ showed the high catalytic activity in Knoevenagel condensation of aromatic aldehydes with active methylene compounds (malononitrile and ethyl cynoacetate). The nanosolid catalyst could be easily recovered by a simple magnetic separation and reused for many cycles without deterioration in catalytic activity.     

Brønsted acidic magnetic nano-Fe3O4-adorned calix[n]arene sulfonic acids: synthesis and application in the nucleophilic substitution of alcohols

Three magnetically recoverable Brønsted acidic calix[n]arene derivatives were successfully constructed by immobilizing calix[n]arene sulfonic acids onto silica-coated magnetic nanoparticles, a process, which allows calix[n]arene derivatives to acquire magnetic properties. All of the magnetically recoverable Brønsted acidic calix[n]arenes efficiently catalyze the coupling of electron-rich arenes with some alcohols in water. After separation and recovery from the reaction mixture by a simple magnet, these Brønsted acidic calix[n]arenes can be recycled many times without losing their catalytic activity.     

Immobilized palladium nanoparticles on MNPs@A‐N‐AEB as an efficient catalyst for C‐O bond formation in water as a green Solvent

Palladium nanoparticles immobilized on the magnetic nanoparticles@2‐amino‐N‐(2‐aminoethyl) benzamide (MNPs@A‐N‐AEB.Pd⁰) have been presented as an efficient, and reusable magnetically heterogeneous catalyst for the C‐O coupling reaction, namely Ullmann condensation reactions in an aqueous medium. This heterogeneous catalyst shows superior reactivity for the C‐O arylation of different aryl halide (chloride, bromide, and iodide) with phenol derivatives to afford the desired products in good to excellent yields within short reaction time. Moreover, the catalyst can be easily recovered and reused for seven runs without loss of catalytic activity. The catalyst was characterized by several techniques, such as FT‐IR, SEM, TEM, EDS, XRD, TGA and ICP‐OES.     

Sulfamic acid immobilized on amino‐functionalized magnetic nanoparticles: A new and active magnetically recoverable catalyst for the synthesis of N‐heterocyclic compounds

Sulfamic acid immobilized on amino‐functionalized magnetic nanoparticles (MNPs/DETA‐SA) was successfully fabricated and characterized using various techniques. Diameters of approximately 15 nm for the MNPs/DETA‐SA were observed from scanning electron microscopy images. The as‐fabricated nanocomposite was applied as an efficient and magnetically reusable catalyst for the synthesis of 2,3‐dihydroquinazoline‐4(1H)‐one and polyhydroquinoline derivatives. All products were obtained in good to excellent yields. Recovery tests confirm that the catalyst can be readily recovered using an external magnet and reused many times without significant loss of its catalytic activity.     

Copper(I) oxide nanoparticles supported on magnetic casein as a bio‐supported and magnetically recoverable catalyst for aqueous click chemistry synthesis of 1,4‐disubstituted 1,2,3‐triazoles

Copper(I) oxide nanoparticles supported on magnetic casein (Cu₂O/Casein@Fe₃O₄NPs) has been synthesized as a bio‐supported catalyst and was characterized using powder X‐ray diffraction, transmission electron microscopy, energy dispersive X‐ray and Fourier transform infrared spectroscopies, thermogravimetric analysis and inductively coupled plasma optical emission spectrometry. The catalytic activity of the synthesized catalyst was investigated in one‐pot three‐component reactions of alkyl halides, sodium azide and alkynes to prepare 1,4‐disubstituted 1,2,3‐triazoles with high yields in water. The reaction work‐up is simple and the catalyst can be magnetically separated from the reaction medium and reused in subsequent reactions.     

Pd on magnetic hybrid of halloysite and POSS-containing copolymer: An efficient catalyst for dye reduction

A novel catalytic nanocomposite, MNPs/Hal-POSS-HEMA-Pd, composed of halloysite nanoclay and polyhedral oligomeric silsesquioxane is reported. To synthesize the catalyst, magnetic halloysite was vinyl functionalized and then polymerized with 2-hydroxyethyl methacrylate and methacrylate polyhedral oligomeric silsesquioxane. Afterwards, the latter was palladated to furnish a heterogeneous catalyst with use for catalyzing the reductive degradation of organic dyes, Rhodamine B, and methyl orange with NaBH₄. The kinetic and thermodynamic parameters of both reactions were estimated. The results asserted that low content of the catalyst could catalyze the dye reduction reactions to furnish hydrogenated product in quantitative conversion in a very short reaction times (1 min). It is assumed that both halloysite and polyhedral oligomeric silsesquioxane can contribute to the anchoring of Pd nanoparticles. On the other hand, the polymeric network around halloysite can furnish a microenvironment for bringing dyes in the vicinity of active sites. Moreover, unique tubular morphology of halloysite can effectively improve dye adsorption and consequently enhance dye reduction. Additionally, the study of the recyclability of the catalyst approved that it could be magnetically recovered and reused for ten successive reaction runs with trivial leach of Pd (2 wt.%) and decrement of the catalytic activity.     

Oxidation of ethylbenzene to styrene oxide in the presence of cellulose‐supported Pd magnetic nanoparticles

Palladium and Fe₃O₄ nanoparticles were deposited on N‐(2‐aminoethyl)acetamide‐functionalized cellulose for use in a catalytic reaction. The catalyst was characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction, energy‐dispersive X‐ray analysis and transmission electron microscopy, and applied in the oxidation reaction of ethylbenzene at 100 °C using H₂O₂. Styrene oxide was obtained as the sole product of the oxidation reaction during 24 h. This reaction has some advantages such as one‐pot transformation of ethylbenzene to styrene oxide, high yield, excellent selectivity and magnetically recoverable catalyst. Also, the recovered catalyst could be used in the oxidation reaction four times without decrease in yield. Copyright © 2016 John Wiley & Sons, Ltd.     

Cyclopropanation of diazoesters with styrene derivatives catalyzed by magnetically recoverable copper-plated iron nanoparticles

Simple bare copper-plated iron nanoparticles catalyzed the cyclopropanation of diazoesters with styrene derivatives. The reaction proceeded smoothly and provided the desired products in moderate to good yields, with selectivity for the trans isomer in neat conditions. The reaction scope was explored and di or tri-substituted cyclopropanes were synthesized. The catalysts could be magnetically separated and reusable up to five times. It was also characterized by TEM, XPS, and ICP-MS. A gram-scale reaction was performed with a yield of 72%.     

Synthesis and characterization of bromine source immobilized on diethylenetriamine‐functionalized magnetic nanoparticles: A novel,versatile and highly efficient reusable catalyst for organic synthesis

Bromine source immobilized on magnetic nanoparticles functionalized with diethylenetriamine was successfully synthesized and characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, vibrating sample magnetometry, thermogravimetric analysis and X‐ray diffraction. The catalytic activity in the synthesis of 2,3‐dihydroquinazoline‐4(1H )‐one and polyhydroquinoline derivatives and in Knoevenagel condensation was studied. The bromine catalyst can be magnetically recovered and reused several times without significant loss of its catalytic activity. All products were obtained in high to excellent yields.     

Synthesis of hierarchical Polystyrene/Polyaniline@Au nanostructures of different surface states and studies of their catalytic properties

We synthesized hierarchical Polystyrene/Polyaniline@Au(PS/PANI@Au) catalysts through a seeded swelling polymerization and in-situ reduction procedure. PS/PANI@Au catalysts possess a core of PS as seed and template, a PANI shell with fibers and uniform gold nanoparticles on the surface. The configuration changes of the PANI chains resulting from the doping/ dedoping procedure led to various loading amounts of Au nanoparticles. Reduction of 4-nitrophenol was chosen as the probe reaction to evaluate the catalytic activity of supported Au nanocatalysts. The catalytic results indicated that dedoping treatment of the PS/PANI supports provides stronger coordinative ability to metal nanoparticles as well as more –N= groups, which results in a better catalytic performance towards the reduction of 4-nitrophenol.