Palladium immobilized on amidoxime‐functionalized magnetic Fe3O4 nanoparticles: a highly stable and efficient magnetically recoverable nanocatalyst for sonogashira coupling reaction

We describe the synthesis of a novel Fe₃O₄/amidoxime (AO)/Pd nanocatalyst by grafting of AO groups on Fe₃O₄ nanoparticles and subsequent deposition of Pd nanoparticles. Prior to grafting of AO, the 2‐cyanoethyl‐functionalized Fe₃O₄ nanoparticles prepared through combining 2‐cyanoethyltriethoxysilane and Fe₃O₄ were treated with hydroxylamine. The AO‐grafted Fe₃O₄ nanoparticles were then used as a platform for the deposition of Pd nanoparticles. The catalyst was characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, scanning and transmission electron microscopies, vibrating sample magnetometry, wavelength‐ and energy‐dispersive X‐ray spectroscopies and inductively coupled plasma analysis. Fe₃O₄/AO/Pd is novel phosphine‐free recyclable heterogeneous catalyst for Sonogashira reactions. Interestingly, the novel catalyst could be recovered in a facile manner from the reaction mixture by applying an external magnet device and recycled seven times without any significant loss in activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Pd–Schiff base complex supported on Fe3O4 magnetic nanoparticles: A new and highly efficient reusable catalyst for C–C bond formation in water

A protocol is introduced for the preparation of a new cage‐like Pd–Schiff base organometallic complex supported on Fe₃O₄ nanoparticles (Fe₃O₄@Schiff‐base‐Pd). The structure of the nanomagnetic catalyst was comprehensively characterized using Fourier transform infrared (FT‐IR) spectroscopy, X‐ray diffraction (XRD), energy‐dispersive X‐ray spectroscopy, Brunauer–Emmett–Teller measurements, scanning electron microscopy (SEM), transmission electron microscopy, X‐ray mapping, thermogravimetric analysis, vibrating sample magnetometry and inductively coupled plasma atomic emission spectroscopy. In the second stage, the catalytic activity of this catalyst was studied in the Suzuki and Heck cross‐coupling reactions in water as a green solvent. In this sense, simple preparation of the catalyst from commercially available materials, high catalytic activity, simple operation, short reaction times, high yields and use of green solvent are some advantages of this protocol. Finally, the nanocatalyst was easily recovered, using an external magnet, and reused several times without significant loss of its catalytic efficiency. In addition, the stability of the catalyst after recycling was confirmed using SEM, XRD and FT‐IR techniques.     

Palladium nanoparticles supported on modified hollow Fe3O4@TiO2: Preparation,characterization, and catalytic activity in Suzuki cross‐coupling reactions

Hollow Fe₃O₄@TiO₂‐NH₂/Pd as a light‐weight, magnetically heterogeneous catalyst was successfully prepared, and characterized by using different techniques including X‐ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR), field‐emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy (EDX), vibrating sample magnetometer (VSM) measurements, and thermogravimetric analysis (TGA). Then this heterogeneous catalyst was tested in the Suzuki cross‐coupling reaction, and the results confirmed the success of this method. The catalyst could be separated easily using an external magnet and reused at least in five runs successfully without any appreciable loss in its catalytic 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.     

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.     

Suzuki and Heck cross‐coupling reactions using ferromagnetic nanoparticle‐supported palladium complex as an efficient and recyclable heterogeneous nanocatalyst in sodium dodecylsulfate micelles

A novel heterogeneous Pd catalyst was synthesized by anchoring Pd(II) onto 4′‐(4‐hydroxyphenyl)‐2,2′:6′,2″‐terpyridine‐coated Fe₃O₄ (FMNPs@TPy‐Pd). This catalyst has been demonstrated for the first time as a recoverable and reusable heterogeneous nanocatalyst in Suzuki and Heck cross‐coupling reactions. The catalyst is very easy to handle and is environmentally safe and economical. FMNPs@TPy‐Pd was characterized using transmission and scanning electron microscopies, X‐ray diffraction, and Fourier transform infrared and energy‐dispersive X‐ray spectroscopies.     

Magnetic nanoporous MCM‐41 supported ionic liquid/palladium complex: An efficient nanocatalyst with high recoverability

In this study, a novel magnetic mesoporous MCM‐41 silica supported ionic liquid/palladium complex (Fe₃O₄@MCM@IL/Pd) with core‐structure was prepared and characterized and its catalytic performance was developed under green conditions. The Fe₃O₄@MCM@IL/Pd was prepared via a post grafting method and was characterized using Fourier transform infrared spectroscopy, thermal gravimetric analysis, wide‐ and low‐angle powder X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, vibration sample magnetometer and energy‐dispersive X‐ray analyses. This was applied as an efficient and recoverable nanocatalyst for the one‐pot synthesis of pyrano[2,3‐d]pyrimidine derivatives under ultrasonic conditions. The catalyst was magnetically recovered and reused for 12 consecutive cycles without significant loss of its activity and selectivity.     

Preparation and characterization of palladium immobilized on silica‐coated Fe3O4 and its catalytic performance for Suzuki reaction under microwave irradiation

Supported palladium catalyst (Pd/Fe₃O₄@SiO₂) was easily prepared by supporting PdCl₂ on silica‐coated magnetic nanoparticles Fe₃O₄ in ethylene glycol. The as‐prepared sample was characterized by infrared spectroscopy (IR), X‐ray diffraction (XRD) and X‐ray photoelectron spectrometer (XPS). The formation of active specie Pd(0) was confirmed by XRD and XPS, and the Pd loading for the fresh and recovered catalyst was determined by atomic absorption spectroscopy (AAS). Pd/Fe₃O₄@SiO₂ was employed for the synthesis of biphenyl derivatives via Suzuki reaction. In terms of the yield of biphenyl, the supported catalyst displayed nearly equal catalytic performance to that of homologous PdCl₂ under microwave irradiation for 30 min but higher than that obtained by traditional heating method for 12 h. The catalytic performance of Pd/Fe₃O₄@SiO₂ for Suzuki reactions involving various aryl halides and arylboronic acids were also examined. Impressive yield of biphenyl at 68.2% was obtained even in the presence of unreactive aryl chlorides. Pd/Fe₃O₄@SiO₂ was recovered by a permanent magnet and directly reused in the next run, and no obvious deactivation was observed for up to 6 times. Copyright © 2016 John Wiley & Sons, Ltd.     

A new nano‐Fe3O4‐supported organocatalyst based on 3,4‐dihydroxypyridine: an efficient heterogeneous nanocatalyst for one‐pot synthesis of pyrazolo[3,4‐b]pyridines and pyrano[2,3‐d]pyrimidines

A simple and practical strategy for the synthesis of a novel nano‐Fe₃O₄‐supported organocatalyst system based on 3,4‐dihydroxypyridine (Fe₃O₄/Py) has been developed. The prepared catalyst was characterized using Fourier transform infrared spectroscopy, transmission and scanning electron microscopies, X‐ray diffraction, vibrating sample magnetometry and energy‐dispersive X‐ray analysis. Accordingly, the Fe₃O₄/Py nanoparticles show a superparamagnetic property with a saturation magnetization of 61 emu g^?1, indicating potential application in magnetic separation technology. Our experimental results reveal that the pyridine‐functionalized Fe₃O₄ nanoparticles are an efficient base catalyst for the domino condensation of various aromatic aldehydes, Meldrum's acid and 5‐methylpyrazol‐3‐amine under very mild reaction condition and in the presence of ethanol solvent. Moreover, the synthesized catalyst was used for one‐pot, three‐component condensation of aromatic aldehydes with barbituric acid and malononitrile to produce 7‐amino‐2,4‐dioxo‐5‐phenyl‐2,3,4,5‐tetrahydro‐1H‐pyrano[2,3‐d]pyrimidine‐6‐carbonitriles. All reactions are completed in short times and all products are obtained in good to excellent yields. Also, notably, the catalyst was reused five times without significant degradation in catalytic activity and performance. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and characterization of a novel magnetic nano‐palladium Schiff base complex: application in cross‐coupling reactions

A novel and task‐specific nano‐magnetic Schiff base ligand with phosphate spacer using 2‐aminoethyl dihydrogen phosphate instead of usual coating agents, i.e. tetraethoxysilane and 3‐aminopropyltriethoxysilane, for coating of nano‐magnetic Fe₃O₄ is introduced. The nano‐magnetic Schiff base ligand with phosphate spacer as a novel catalyst was synthesized and fully characterized using infrared spectroscopy, X‐ray diffraction, scanning and transmission electron microscopies, thermogravimetry, derivative thermogravimetry, vibrating sample magnetometry, atomic force microscopy, X‐ray photoelectron spectroscopy and energy‐dispersive X‐ray spectroscopy. The resulting task‐specific nano‐magnetic Schiff base ligand with phosphate spacer was successfully employed as a magnetite Pd nanoparticle‐supported catalyst for Sonogashira and Mizoroki–Heck C–C coupling reactions. To the best of our knowledge, this is the first report of the synthesis and applications of magnetic nanoparticles of Fe₃O₄@O₂PO₂(CH₂)₂NH₂ as a suitable spacer for the preparation of a designable Schiff base ligand and its corresponding Pd complex. So the present work can open up a new and promising insight in the course of rational design, synthesis and applications of various task‐specific magnetic nanoparticle complexes. Copyright © 2016 John Wiley & Sons, Ltd.     

Betti base‐modified magnetic nanoparticles as a novel basic nanocatalyst in Knoevenagel condensation and its related palladium nanocatalyst in Suzuki coupling reactions

Betti base‐modified Fe₃O₄ nanoparticles have been successfully designed and synthesized for the first time through the condensation of Fe₃O₄ magnetic nanoparticles coated by (3‐aminopropyl)triethoxysilane with β‐naphthol and benzaldehyde. Their application as a novel magnetic nanocatalyst in the Knoevenagel condensation and also application to immobilization of palladium nanoparticles for Suzuki coupling reactions have been investigated which opens a new field for application of Betti base derivatives in organic transformations. The synthesized inorganic–organic hybrid nanocatalyst has been fully been characterized using Fourier transform infrared, X‐ray diffraction, vibrating sample magnetometry, transmission and scanning electron microscopies, energy‐dispersive X‐ray, wavelength‐dispersive X‐ray and X‐ray photoelectron spectroscopies and inductively coupled plasma techniques. The catalyst was easily separated with the assistance of an external magnet from the reaction mixture and reused for several consecutive runs with no significant loss of its catalytic efficiency. Copyright © 2016 John Wiley & Sons, Ltd.     

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.     

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.     

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.     

Highly stable magnetically separable copper nanocatalyst as an efficient catalyst for C(sp2)–C(sp) and C(sp2)–C(sp2) cross‐coupling reactions

A copper catalyst has been explored as an efficient and recyclable catalyst to effect Sonogashira and Suzuki cross‐coupling reactions. After modification of 2‐(((piperazin‐1‐ylmethyl)imino)methyl)phenol (PP) on the surface of amorphous silica‐coated iron oxide (Fe₃O₄@SiO₂@Cl) magnetic core–shell nanocomposite, copper(II) chloride was employed to synthesize the Fe₃O₄@SiO₂@PP‐Cu catalyst, affording a copper loading of 1.52 mmol g⁻¹. High yield, low reaction times, non‐toxicity and recyclability of the catalyst are the main merits of this protocol. The catalyst was characterized using Fourier transform infrared, X‐ray photoelectron, energy‐dispersive X‐ray and inductively coupled plasma optical emission spectroscopies, X‐ray diffraction, scanning and transmission electron microscopies, and vibrating sample magnetometry.     

Magnetic Fe3O4 nanoparticles supported imine/Thiophene‐nickel (II) complex: A new and highly active heterogeneous catalyst for the synthesis of polyhydroquinolines and 2, 3‐dihydroquinazoline‐4(1H)‐ones

A new magnetically separable nickel catalyst (Ni(NO₃)_2?Imine/Thiophene‐Fe₃O₄@SiO₂) was readily prepared and structurally characterized by Fourier transform infrared spectroscopy (FT‐IR), Scanning electron microscopy (SEM), Energy‐dispersive X‐ray spectroscopy (EDX), Vibrating sample magnetometer (VSM), X‐Ray diffraction (XRD) and Atomic absorption spectroscopy (AAS). The Ni(NO₃)_2?Imine/Thiophene‐Fe₃O₄@SiO₂ exhibited efficient catalytic activity in the synthesis of 2,3‐dihydroquinazoline‐4(1H)‐ones and polyhydroquinolines. Catalysis research under water and solvent‐free conditions makes also this synthetic protocol ideal and fascinating from the environmental point of view. The catalyst can be magnetically recovered after the reaction and can be reused for many times without appreciable decrease in activity.     

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.     

Fe3O4‐supported Schiff‐base copper (II) complex: A valuable heterogeneous nanocatalyst for one‐pot synthesis of new pyrano[2,3‐b]pyridine‐3‐carboxamide derivatives

A novel Cu (II) Schiff‐base complex immobilized on core‐shell magnetic Fe₃O₄ nanoparticles (Fe₃O₄@SPNC) was successfully designed and synthesized. The structural features of these nanoparticles were studied and confirmed by using various techniques including FT‐IR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy (EDS), vibrating sample magnetometer (VSM), X‐Ray diffraction (XRD), wavelength dispersive X‐ray spectroscopy (WDX), and inductively coupled plasma (ICP). These newly synthesized nanoparticles have been used as efficient heterogeneous catalytic system for one‐pot multicomponent synthesis of new pyrano[2,3‐b]pyridine‐3‐carboxamide derivatives. Notably, the catalyst could be easily separated from the reaction mixture by using an external magnet and reused for several successive reaction runs with no significant loss of activity or copper leaching. The present protocol benefits from a hitherto unreported MNPs‐immobilized Cu (II) Schiff‐base complex as an efficient nanocatalyst for the synthesis of newly reported derivatives of pyrano[2,3‐b]pyridine‐3‐carboxamide from one‐pot multicomponent reactions.     

Preparation and characterization of hexamethylenetetramine‐functionalized magnetic nanoparticles and their application as novel catalyst for the synthesis of pyranopyrazole derivatives

A new magnetic catalyst was prepared through the reaction of silanol groups, on the surface of silica‐coated Fe₃O₄ magnetic nanoparticles, with (3‐chloropropyl)triethoxysilane followed by hexamethylenetetramine and chlorosulfonic acid. The obtained magnetic catalyst was characterized using thermogravimetric analysis, vibrating sample magnetometry, scanning electron microscopy and energy‐dispersive X‐ray analysis. Its catalytic activity was investigated in the synthesis of pyranopyrazole compounds, and the results were excellent regarding high yield of the products and short reaction time.     

Synthesis of a novel and reusable biological urea based acidic nanomagnetic catalyst: Application for the synthesis of 2‐amino‐3‐cyano pyridines via cooperative vinylogous anomeric based oxidation

In the current study, a novel and reusable biological urea based nano magnetic catalyst namely Fe₃O₄@SiO₂@(CH₂)₃‐urea‐benzimidazole sulfonic acid was designed and synthesized. The structure of the titled catalyst was fully characterized using several skills including Fourier transform infrared (FT‐IR) spectroscopy, energy dispersive X‐ray (EDX) analysis, X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermo gravimetric analysis/differential thermal analysis (TG/DTG) and vibrating sample magnetometer (VSM). Then, the catalytic performance of Fe₃O₄@SiO₂@(CH₂)₃‐urea‐benzimidazole sulfonic acid was successfully inspected towards the multicomponent synthesis of 2‐amino‐3‐cyano pyridine derivatives through a vinylogous anomeric based oxidation pathway.