Fe3O4@SiO2@sulfated boric acid as superparamagnetic and recyclable nanocatalyst‐assisted,one‐pot,pseudo four‐component synthesis of 5‐amino‐2‐aryl‐3H‐chromeno[4,3,2‐de][1,6]naphthyridine‐4‐carbonitrile derivatives

The catalytic performance of the superparamagnetic nanocatalyst Fe₃O₄@SiO₂@Sulfated boric acid as a green, recyclable, and acidic solid catalyst in the synthesis of chromeno[4,3,2‐de][1,6]naphthyridine derivatives has been studied. Chromeno[4,3,2‐de][1,6]naphthyridine derivatives via a pseudo four‐component reaction from aromatic aldehydes (1 mmol), malononitrile (2 mmol), and 2′‐hydroxyacetophenone in the presence of Fe₃O₄@SiO₂@Sulfated boric acid (0.004 g) as a nanocatalyst in 3 mL of water as a green solvent at 80°C has been synthesized. The advantages of this method are higher product yields in shorter reaction times, easy recyclability and reusability of the catalyst, and easy work‐up procedures. The nanocatalyst was reused at least six times. The nanocatalyst retained its stability in the reaction, and after reusability, it was separated easily from the reaction by an external magnet.     

Fe3O4@SiO2@l‐arginine@Pd(0): a new magnetically retrievable heterogeneous nanocatalyst with high efficiency for C–C bond formation

The surface of Fe₃O₄@SiO₂ nanoparticles was modified using l ‐arginine as a green and available amino acid to trap palladium nanoparticles through a strong interaction between the metal nanoparticles and functional groups of the amino acid. The proposed green synthetic method takes advantage of nontoxic reagents through a simple procedure. Characterization of Fe₃O₄@SiO₂@l ‐arginine@Pd(0) was done using Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, X‐ray diffraction, vibrating sample magnetometry and inductively coupled plasma analysis. The catalytic activity of Fe₃O₄@SiO₂@l ‐arginine@Pd(0) as a new nanocatalyst was investigated in C – C coupling reactions. Waste‐free, use of green medium, efficient synthesis leading to high yield of products, eco‐friendly and economic catalyst, excellent reusability of the nanocatalyst and short reaction time are the main advantages of the method presented. Copyright © 2016 John Wiley & Sons, Ltd.     

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.     

Fe3O4@SiO2/Schiff base complex of metal ions as an efficient and recyclable nanocatalyst for the green synthesis of quinoxaline derivatives

Fe₃O₄@SiO₂/Schiff base complex of metal ions catalyzed the reaction between phenylene-1,2-diamines and 1,2-diketones to produce quinoxalines in aqueous media at room temperature. This eco-friendly method provides several advantages such as mild reaction conditions, good to excellent yields, simple work-up, and nanocatalyst stability. Also, nanocatalyst can be simply recovered by a magnetic field and reused for at least five successive reactions.     

Synthesis and characterization of a novel Fe3O4@SiO2/bipyridinium dichloride nanocomposite and its application as a magnetic and recyclable phase-transfer catalyst in the preparation of β-azidoalcohols, β-cyanohydrins,and β-acetoxy alcohols

β-Azidoalcohols, β-cyanohydrins, and β-acetoxy alcohols have been synthesized in the presence of a Fe₃O₄@SiO₂/bipyridinium nanocomposite (Fe₃O₄@SiO₂/BNC) as a novel magnetic and recyclable phase-transfer catalyst (PTC) in water. The catalyst was characterized with FT–IR, SEM, XRD, VSM, and TGA. This methodology offers several advantages, including easy work-up procedure, excellent regioselectivity, high yields, short reaction times, recyclable catalyst, easy separation of the catalyst through an external magnet and eco-friendly procedure.     

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.     

Synthesis of a new schiff base oxovanadium complex with melamine and 2‐hydroxynaphtaldehyde on modified magnetic nanoparticles as catalyst for allyl alcohols and olefins epoxidation

A new magnetically recoverable nanocatalyst designated as Fe₃O₄@SiO₂@PTMS@Mel‐Naph‐VOcomplex was synthesize by covalent binding of a Schiff base ligand derived from melamine and 2‐hydroxy1naphtaldehyde on the surface of silica coated iron oxide magnetic nanoparticles followed by complexation with VO (acac)₂. Characterization of the prepared nanocatalyst was accomplished with FT‐IR, XRD, SEM, HRTEM, VSM and atomic absorption techniques. It was found that the epoxidation of geraniol, trans‐2‐hexen‐1‐ol, 1‐octen‐3‐ol, norbornene, and cyclooctene is highly selective, affording quantitative yields of the corresponding epoxides with tert‐butyl hydroperoxide (TBHP) using Fe₃O₄@SiO₂@Mel‐Naph‐VOcomplex as catalyst. High reaction yields, short reaction times, simple experimental and work up procedure, catalyst stability and excellent reusability even after five‐cycles of usage in the case of geraniol are some advantages of this research.     

New magnetic supported hydrazone Schiff base dioxomolybdenum (VI) complex: An efficient nanocatalyst for epoxidation of cyclooctene and norbornene

A new dioxomolybdenum (VI) complex with tridentate hydrazone Schiff base ligand (H₂L) derived from 2‐hydroxy‐5‐nitrobenzaldehyde and benzhydrazide was synthesized and designated as [MoO₂L (DMF)]·2H₂O. The Fe₃O₄@SiO₂‐CPS‐L‐MoO₂ (EtOH) nanocatalyst was successfully prepared by grafting H₂L ligand on modified Fe₃O₄ nanoparticles followed by reacting with MoO₂ (acac)₂. The complex and nanocatalyst were characterized by various techniques such as elemental analysis, mass, FT‐IR, UV–Vis, ¹H NMR, ¹³C{¹H}‐NMR, TGA, XRD, XPS, TEM, SEM and VSM. The catalytic activity of [MoO₂L (DMF)]2H₂O and Fe₃O₄@SiO₂‐CPS‐L‐MoO₂ (EtOH) were evaluated for the oxidation of various alkenes (cyclooctene, norbornene, cyclohexene, styrene and α‐methyl styrene) in the presence of tert‐butylhydroperoxide as oxidant. The results revealed that the catalysts were especially efficient for oxidation of cyclooctene and norbornene with 100% selectivity towards corresponding epoxide product. Fe₃O₄@SiO₂‐CPS‐L‐MoO₂ (EtOH) showed higher catalytic activity, shorter reaction time and higher turnover number (TON) compared with homogeneous complex [MoO₂L (DMF)]·2H₂O. Moreover, simple magnetic recovery from the reaction mixture and reuse for several times with no significant loss in activity were other advantages of the nanocatalyst.     

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.     

Synthesis of benzo[b]xanthene-triones and tetrahydrochromeno[2,3-b]xanthene tetraones via three- or pseudo–five-component reactions using Fe3O4@SiO2/PEtOx as a novel,magnetically recyclable,and eco-friendly nanocatalyst

In this study, poly(2-ethyl-2-oxazoline) (PEtOx) immobilized on Fe₃O₄ nanoparticles (Fe₃O₄@SiO₂/PEtOx) has been constructed as a new, heterogeneous, efficient, and recyclable nanocatalyst. The prepared nanocatalyst was characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) analysis, and vibrating-sample magnetometer (VSM) techniques. Nanocatalyst was employed to synthesize benzo[b]xanthene-triones and tetrahydrochromeno[2,3-b]xanthene tetraones via one-pot three- or pseudo–five-component reaction between 2-hydroxy-1,4-naphthoquinone or 2,5-dihydroxy-1,4-benzoquinone, aldehyde, and dimedone or 1,3-cyclohexanedione under reflux condition in ethanol. The catalyst could be easily separated and recycled several times without considerable loss of activity. Clean methodology, easy work-up, mild reaction condition, short reaction time with good-to-excellent yields, and simple preparation of the catalyst are some advantages of the presented work.     

Copper–birhodanine complex immobilized on Fe3O4 nanoparticles: DFT studies and heterogeneous catalytic applications in the synthesis of propargylamines in aqueous medium

Heterogeneous magnetic nanocatalyst, Fe₃O₄@SiO₂–Ligand–Cu (II) MNPs, reveals high catalytic performance within the synthesis of propargylamines using the multicomponent coupling reaction of aldehydes, phenylacetylene and secondary amines in water as a solvent. The substantial feature of this organic–inorganic hybrid magnetic nanocatalyst is the capability of straightforward separation of the reaction mixture by an external magnet which was retrieved ten times without significant loss of catalytic activity. This methodology has other advantages such as subordination to the principles of green chemistry and avoiding the use of expensive and harmful organic solvents. To study the stability and actual structure of birhodanine derivative–copper (II) complex, DFT calculations were also performed.     

Hiyama cross‐coupling reaction using Pd(II) nanocatalyst immobilized on the surface of Fe3O4@SiO2

We report a simple process for the synthesis of Fe₃O₄@SiO₂/APTMS (APTMS = 3‐aminopropyltrimethoxysilane) core–shell nanocatalyst support. The new nanocatalyst was prepared by stabilization of Pd(cdha)₂ (cdha = bis(2‐chloro‐3,4‐dihydroxyacetophenone)) on the surface of the Fe₃O₄@SiO₂/APTMS support. The structure and composition of this catalyst were characterized using various techniques. An efficient method was developed for the synthesis of a wide variety of biaryl compounds via fluoride‐free Hiyama cross‐coupling reactions of aryl halides with arylsiloxane, with Fe₃O₄@SiO₂/APTMS/Pd(cdha)₂ as the catalyst under reaction conditions. This methodology can be performed at 100°C through a simple one‐pot operation using in situ generated palladium nanoparticles. High catalytic activity, quick separation of catalyst from products using an external magnetic field and use of water as green solvent are attributes of this protocol.     

Novel design of recyclable copper(II) complex supported on magnetic nanoparticles as active catalyst for Beckmann rearrangement in poly(ethylene glycol)

Copper complex‐functionalized magnetic core–shell nanoparticles (Fe₃O₄@SiO₂‐Lig‐Cu) were prepared and characterized using various techniques. The activity of the new catalyst was tested for the Beckmann rearrangement. The reaction conditions allow for the conversion of a wide variety of aldoximes, including aromatic and heterocyclic ones, to amides in good to excellent yields. High efficiency, mild reaction conditions, easy work‐up, use of poly(ethylene glycol) as a green medium and simple purification of products are important advantages of this system. Moreover, the eco‐friendly heterogeneous nanocatalyst could be easily recovered from the reaction mixture using an external magnet and reused several times.     

Encapsulation of palladium chloride using 2‐formylbenzoic acid supported by Fe3O4 nanoparticles modified with SiO2 and propylamine,its characterization and its application for Suzuki coupling reaction

A magnetically separable heterogeneous nanocatalyst, Fe₃O₄@SiO₂(CH₂)₃N―CH―Ar@Pd(0), was simply prepared and characterized using various techniques. The catalytic activity of this nanocatalyst was evaluated via the Suzuki–Miyaura cross‐coupling reaction of aryl halides with phenylboronic acid under various experimental conditions such as kind of base, solvent and temperature. This nanocatalyst is completely magnetically recoverable because of the superparamagnetic behaviour of Fe and can be reused with sustained selectivity and activity.     

Fe3O4@SiO2–NH2 core-shell nanocomposite as an efficient and green catalyst for the multi-component synthesis of highly substituted chromeno[2,3-b]pyridines in aqueous ethanol media

ABSTRACT

An efficient and green approach for synthesizing chromeno[2,3-b]pyridine derivatives through one-pot three-component reactions of salicylaldehydes, thiols, and malononitrile has been developed by Fe₃O₄@SiO₂–NH₂ nanocatalyst in aqueous ethanol media under re?ux conditions. The present procedure provides several advantages such as environmentally benign, straightforward, excellent yields, short reaction times, cost-effective, good recyclability, little catalyst loading, and facile catalyst separation for the preparation of chromeno[2,3-b]pyridines as important privileged medicinal scaffold. In addition, aminopropyl-coated Fe₃O₄@SiO₂ nanoparticles were fully characterized by scanning electron microscopy, X-ray diffraction, energy dispersive analysis of X-ray, vibrating sample magnetometer, and FT-IR analysis.     

Silver,iron, and nickel immobilized on hydroxyapatite‐core‐shell γ‐Fe2O3 MNPs catalyzed one‐pot five‐component reactions for the synthesis of tetrahydropyridines by tandem condensation of amines,aldehydes, and methyl acetoacetate

In this study, Ag, Ni²⁺, and Fe²⁺ immobilized on hydroxyapatite‐core‐shell γ‐Fe₂O₃ nanoparticles (γ‐Fe₂O₃@HAp‐Ag, γ‐Fe₂O₃@HAp‐Ni²⁺, and γ‐Fe₂O₃@HAp‐Fe²⁺) as a new and reusable Lewis acid magnetic nanocatalyst was successfully synthesized and reported for an atom economic, extremely facile, and environmentally benign procedure for the synthesis of highly functionalized tetrahydropyridines derivatives 4a‐t is described by one‐pot five‐component reaction of 2 equiv of aldehydes 1 , 2 equiv of amines 2 , and 1 equiv of methyl acetoacetate 3 in EtOH at room temperature in good to high yields and short reaction time. The presented methodology offers several advantages such as easy work‐up procedure, reusability of the magnetic nanocatalyst, operational simplicity, green synthesis avoiding toxic reagents and solvent, mild reaction conditions, and no tedious column chromatographic separation.     

Preparation of a trihydrazinotriazine-functionalized core-shell nanocatalyst as an extremely efficient catalyst for the synthesis of benzoxanthenes

In recent years, there is a high demand on utilizing heterogeneous nanocatalysts in organic synthetic routes because of their green approach, facile purification of the products, and reusability of the catalyst. Herein, we introduced trihydrazinotriazine (THDT)-coated Fe₃O₄@SiO₂ as a novel amino-functionalized magnetic nanocompostie. We fully characterized the nanocatalyst and proved the morphology and magnetic property of the nanoparticles by using essential analyses. The basic attribute of the amino-rich porous surface of the nanocomposite provides a desirable environment for enhancing various reaction conditions. To examine the applicability of the nanocatalyst in organic reactions, we synthesized several benzoxanthenes using Fe₃O₄@SiO₂-THDT nanocatalysts. The nanocomposite successfully improved the reaction conditions and provided the benzoxanthenes in an environmentally friendly procedure, which afforded product in excellent yields (80–96%) and reduced time. The nanomagnetic catalyst was easily recovered after each trial by using an external magnet. After six successive runs, the loss of catalytic activity of the nanocomposite was negligible. Finally, we propounded a plausible mechanism for the preparation of the benzoxanthenes derivatives using the THDT-functionalized core-shell magnetic nanocatalyst.     

Synthesis,characterization and application of Fe3O4@SiO2@CPTMO@DEA-SO3H nanoparticles supported on bentonite nanoclay as a magnetic catalyst for the synthesis of 1,4-dihydropyrano[2,3-c]pyrazoles

Fe₃O₄ nanoparticles were prepared and decorated on the surface of nanobentonite (NB), and subsequently modified by the organic and inorganic linkers and then sulfonic acid immobilization on the nanoparticles. The NB-Fe₃O₄@SiO₂@CPTMO@DEA-SO₃H catalyst was characterized via Fourier transform-infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, vibrating-sample magnetometer, X-ray diffraction patterns, Brunauer–Emmett–Teller and thermal gravimetric analysis. The new catalyst benefits from a simple preparation method, and environmentally friendly and high magnetic properties of the nanocatalyst, Accordingly, we used it for the synthesis of dihydropyrano[2,3c]pyrazole derivatives in water and ethanol mixture as a green solvent under reflux conditions. Use of mild conditions, easy catalyst separation, cost-effectiveness, short reaction time, reusability of the catalyst, excellent yield and easy work-up are the main advantages of the present method.     

Synthesis of Novel Triazole Incorporated Thiazolone Motifs Having Promising Antityrosinase Activity through Green Nanocatalyst CuI-Fe3O4@SiO2 (TMS-EDTA)

In the present work, novel 5-((1-benzyl-1,2,3-triazol-4-yl)methoxybenzylidene)-2-(arylamino)thiazol-4-one thiazolone incorporated triazole derivatives have been designed as tyrosinase inhibitors. The compounds were synthesized through click reaction in good yield. Moreover, the antityrosinas activity of the synthesized derivatives was evaluated. In the search for establishing a click copper-catalyzed azide/alkyne cycloaddition (CuAAC) reaction under strict conditions, in terms of a novel air-stable, a recyclable and efficient magnetic catalyst was planned for new triazole derivatives as a well-organized copper iodide supported on the functionalized Fe₃O₄@SiO₂ core-shell (CuI/Fe₃O₄@SiO₂(TMS-EDTA) nanoparticles). The engineered nanocatalyst synthesized for the first time and characterized by different methods, including FT-IR spectroscopy, XRD, FESEM, EDX, TEM, TGA, and BET analysis. The excellent catalytic performance in ethanol with high surface area (351.7 m²g⁻¹) and short reaction time for diverse functional groups (120–200 min), no use of toxic solvents, reusability of the catalyst, and using eco-friendly conditions are the advantageous of this work. Moreover,the nanocatalyst can be used at least five times without any significant decrease in the yield of the reaction. The thiazolidine-triazole derivatives 9a , 9c , 9e , and 9 g showed promising tyrosinase inhibitory activity with IC₅₀ values in the range of 5.90–9.81 μM. The compounds were found to be considerably more potent tyrosinase inhibitors than the reference inhibitor kojic acid (IC₅₀ = 18.36 μM).     

CoFe2O4@SiO2-NH2-CoII NPs catalyzed Hantzsch reaction as an efficient,reusable catalyst for the facile,green, one-pot synthesis of novel functionalized 1,4-dihydropyridine derivatives

A magnetically heterogeneous CoFe₂O₄@SiO₂-NH₂-Co^II nanoparticle was synthesized by the immobilization of Co (II) complex onto CoFe₂O₄@SiO₂ nanoparticles, and the heterogeneous magnetic nanocatalyst was characterized by XRD, TEM, TGA, EDX, and FT-IR techniques. Then, the green and reusable method was introduced for a multicomponent synthesis of 1,4-dihydropyridine derivatives via Hantszch reaction. The synthesis of 1,4-dihydropyridine derivatives was proceeded by the reaction of aldehyde, ethyl acetoacetate, and ammonium acetate in the presence of this magnetic nanocatalyst in EtOH/Water (1:1). Simple work-up, short reaction times, excellent yields (60–96%) as well as green solvent are some advantages of this novel approach, and the corresponding products were purified with no need for chromatographic separation.