New metal complexes supported on Fe3O4 magnetic nanoparticles as recoverable catalysts for selective oxidation of sulfides to sulfoxides

Fe₃O₄ nanoparticles were coated with aminopropyltriethoxysilane and subsequently reacted with isatin to obtain imine‐bonded Fe₃O₄ nanoparticles. The addition of ZrOCl₂?8H₂O or CuCl₂ led to the formation of complexes of Zr(IV)/isatin@Fe₃O₄ or Cu (II)/isatin@Fe₃O₄ as new magnetically separable catalysts. The synthesized catalysts were characterized using various techniques. These catalysts are shown to be efficient for chemo‐selective oxidation of sulfides to sulfoxides using hydrogen peroxide as oxidative agent. This system has many advantages, such as excellent level of reusability of magnetic catalysts, high yields, simplicity of separation of catalysts using an external magnet, environmental benignity and ease of handling. Copyright © 2016 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.     

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.     

Fe3O4 nanoparticles/ethyl acetoacetate system for the efficient catalytic oxidation of aldehydes to carboxylic acids

A new methodology for the oxidation of aldehydes promoted by commercially available Fe₃O₄ nanoparticles (Fe₃O₄ NPs) activated by ethyl acetoacetate was developed. The use of ethyl acetoacetate as additive was crucial to achieve high reactivities. All reactions were realized under solvent free conditions, using air or tBuOOH as oxidants. Finally, the separation and reuse of the magnetically recoverable nanoparticles make this methodology very practical, simple and economical.     

Applications of iron and nickel immobilized on hydroxyapatite‐core‐shell γ‐Fe2O3 as a nanomagnetic catalyst for the chemoselective oxidation of sulfides to sulfoxides under solvent‐free conditions

In the present study, Fe²⁺ and Ni²⁺ immobilized on hydroxyapatite‐core‐shell γ‐Fe₂O₃ (γ‐Fe₂O₃@HAp‐Fe²⁺ and γ‐Fe₂O₃@HAp‐Ni²⁺) with a high surface area has been synthesized and characterized by Fourier transform infrared (FTIR), X‐ray diffraction (XRD), vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), and scanning electron microscope (SEM) techniques. Then, γ‐Fe₂O₃@HAp‐Fe²⁺ and γ‐Fe₂O₃@HAp‐Ni²⁺ were used as a new and magnetically recoverable nano catalyst for the selective oxidation of sulfides to sulfoxides with 33% aqueous H₂O₂ (0.5 mL) as an oxidant at room temperature in good to excellent yields and short reaction time. Nontoxicity of reagent, mild reaction condition, inexpensive and high catalytic activity, simple experimental procedure, short period of conversion and excellent yields, and ease of recovery from the reaction mixture using an external magnet are the advantages of the present method.     

Immobilized manganese porphyrin on functionalized magnetic nanoparticles via axial ligation: efficient and recyclable nanocatalyst for oxidation reactions

Magnetic nanoparticles (MNPs), Fe₃O₄@SiO₂, have been prepared and functionalized by 3-(chloropropyl)trimethoxysilane and then by imidazole to synthesize Fe₃O₄@SiO₂-Im. The functionalized Fe₃O₄ nanoparticles were used as a support to anchor manganese porphyrin via axial ligation. The prepared catalyst was characterized by elemental analysis, FT-IR spectroscopy, X-ray powder diffraction, UV–vis spectroscopy, and scanning electron microscopy. Application of immobilized manganese porphyrin as a heterogeneous catalyst in oxidation of alkenes and sulfides was explored. To find suitable reaction conditions, effect of different parameters such as solvent and temperature on immobilization process and also various reaction parameters (oxidant, solvent, and time) on oxidation reactions has been investigated. The results showed that the immobilized Mn-porphyrin on functionalized MNPs is an efficient and reusable catalyst for oxidation of substrates.     

Fe3O4@dopa (dopa = dopamine hydrochloride) functionalized Mn(III) Schiff base complex: A promising magnetically separable heterogeneous catalyst for oxidative transformations

A chiral Schiff base complex has been prepared by treating (R)-1,2-diaminopropane with 3,5-dichlorosalicylaldehyde in ethanol, followed by addition of manganese chloride hexahydrate to generate a homogeneous catalyst, [MnL(Cl)(H₂O)] (HMN). Crystal structure of the complex reveals its mononuclear nature. Circular dichroism (CD) studies indicate that the ligand and its corresponding complex contain an asymmetric center. The catalytic activity of HMN toward epoxidation of alkenes, oxidation of alcohols and oxidation of alkanes has been investigated in the presence of iodosylbenzenediacetate (PhI(OAc)₂), in acetonitrile. In the present work we found yields to be much higher compared to our previous approaches. For further adaptation, we attached our efficient homogeneous catalyst with surface modified magnetic nanoparticles (Fe₃O₄@dopa) and thereby obtained a new magnetically separable nanocatalyst Fe₃O₄@dopa@MnLCl (FDM). This catalyst has been characterized and its oxidation ability assessed in similar conditions as those used for the homogeneous catalyst. Enantiomeric excess in epoxide yield reveals retention of chirality of the active site of Fe₃O₄@dopa@MnLCl. The catalyst can be recovered by magnetic separation and recycled several times without significant loss of catalytic activity.     

Surface-enhanced Raman scattering from magneto-metal nanoparticle assemblies

Binary nanoparticles composed of a superparamagnetic Fe₃O₄ core and an Au nanoshell (Fe₃O₄@Au) were prepared via a simple co-precipitation method followed by seed-mediated growth process. The nanoparticles exhibited functions of both fast magnetic response and local surface plasmon resonance. The Fe₃O₄@Au nanoparticles were used as probes for surface-enhanced Raman scattering (SERS) using p-thiocresol (p-TC) as reporter molecule. With the ability of analyte capture and concentration magnetically, the Fe₃O₄@Au nanoparticles showed significant SERS properties with excellent reproducibility. Under non-optimized conditions, detection limit as low as 4.55 pM of analyte can be reached using Fe₃O₄@Au nanoparticle assemblies, which excel remarkably the cases with traditional Au nanoprobes.     

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.     

Magnetically Encoded Luminescent Composite Nanoparticles through Layer‐by‐Layer Self‐Assembly

Sensitive and rapid detection of multiple analytes and the collection of components from complex samples are important in fields ranging from bioassays/chemical assays, clinical diagnosis, to environmental monitoring. A convenient strategy for creating magnetically encoded luminescent CdTe@SiO₂@n Fe₃O₄ composite nanoparticles, by using a layer‐by‐layer self‐assembly approach based on electrostatic interactions, is described. Silica‐coated CdTe quantum dots (CdTe@SiO₂) serve as core templates for the deposition of alternating layers of Fe₃O₄ magnetic nanoparticles and poly(dimethyldiallyl ammonium chloride), to construct CdTe@SiO₂@n Fe₃O₄ (n=1, 2, 3, …?) composite nanoparticles with a defined number (n) of Fe₃O₄ layers. Composite nanoparticles were characterized by zeta‐potential analysis, fluorescence spectroscopy, vibrating sample magnetometry, and transmission electron microscopy, which showed that the CdTe@SiO₂@n Fe₃O₄ composite nanoparticles exhibited excellent luminescence properties coupled with well‐defined magnetic responses. To demonstrate the utility of these magnetically encoded nanoparticles for near‐simultaneous detection and separation of multiple components from complex samples, three different fluorescently labeled IgG proteins, as model targets, were identified and collected from a mixture by using the CdTe@SiO₂@n Fe₃O₄ nanoparticles.     

Synthesis of Chromene Derivatives via Three‐Component Reaction of 4‐hydroxycumarin Catalyzed by Magnetic Fe3O4 Nanoparticles in Water

An easy and effective procedure for one‐pot three components coupling of 4‐hydroxycumarin, isothiocyanates, and isocyanides in water by employing magnetically recoverable Fe₃O₄ nanoparticles is described. Variety of chromene were produced a derivatives in high yields by using of this procedure. The catalyst can be recovered and recycled without a considerable decrease in the catalytic activity.     

Enhanced reactivity in a heterogeneous oxido-peroxido molybdenum(VI) complex of salicylidene 2-picoloyl hydrazone in catalytic epoxidation of olefins

A molybdenum(VI) oxido-diperoxido complex of salicylidene 2-picoloyl hydrazine (sal-phz) was synthesized and successfully grafted onto chloro-functionalised Fe₃O₄ nanoparticles. The resulting heterogeneous and magnetically recoverable nanoscale catalyst MoO₃(sal-phz)/Fe₃O₄ was characterized by physicochemical and spectroscopic techniques. The activity of this heterogeneous catalyst for the oxidation of olefins to corresponding epoxides was efficiently increased by increasing the reaction temperature up to 95 °C. The nanocatalyst proved to be efficient for the selective epoxidation of a variety of alkenes using t-BuOOH with high conversion and selectivity. Leaching and recycling tests showed that the nanocatalyst can be reused at least six times without significant decrease in efficiency.     

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.     

Palladium nanoparticle‐decorated magnetic pomegranate peel‐derived porous carbon nanocomposite as an excellent catalyst for Suzuki–Miyaura and Sonogashira cross‐coupling reactions

Porous carbon (PC) material was prepared from the carbonization of pomegranate peel waste. Subsequently, magnetically separable Fe₃O₄@PC was synthesized from Fe₃O₄ nanoparticles decorated on PC by the co‐precipitation method of iron ions. Finally, Fe₃O₄@PC was successfully decorated with palladium nanoparticles in a simple route by reducing H₂PdCl₄ in the presence of sodium dodecylsulfate, which was used as both surfactant and reducing agent. Additionally, the effect of temperature on the carbonization process was studied. The Pd/Fe₃O₄@PC nanocomposite was used as an efficient and heterogeneous catalyst for Suzuki–Miyaura and Sonogashira cross‐coupling reactions in an environmentally friendly medium.     

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.     

Magnetically recyclable Schiff-based palladium nanocatalyst [Fe3O4@SiNSB-Pd] and its catalytic applications in Heck reaction

A magnetically separable palladium nanocatalyst has been synthesized through the immobilization of palladium onto 3-aminopropylphenanthroline Schiff based functionalized silica coated superparamagnetic Fe₃O₄ nanoparticles. The nanocatalyst (Fe₃O₄@SiNSB-Pd) was fully characterized using several spectroscopic techniques, such as FT-IR, HR-SEM, TEM, XRD, ICP, and XPS. The microscopic image of Fe₃O₄ showed spherical shape morphology and had an average size of 150 nm. The Pd-nanoparticles exhibited an average size 3.5 ± 0.6 nm. The successful functionalization of Fe₃O₄@SiNSB-Pd was identified by FT-IR spectroscopy and the appearance of palladium species in Fe₃O₄@SiNSB-Pd was confirmed by XRD analysis. While XPS has been utilized for the determination of the chemical oxidation state of palladium species in Fe₃O₄@SiNSB-Pd. Several activated and deactivated arene halides and olefines were employed for Mizoroki-Heck cross-coupling reactions in the presence of Fe₃O₄@SiNSB-Pd, each of which produced the respective cross-coupling products with excellent yields. The Fe₃O₄@SiNSB-Pd shows good reactivity and reusability for up to seven consecutive cycles.     

Fe3O4@S‐ABENZ@VO: Magnetically separable nanocatalyst for the efficient,selective and mild oxidation of sulfides and oxidative coupling of thiols

Oxovanadium(IV) immobilized on Fe₃O₄@S‐ABEN is reported as a highly efficient nanocatalyst for the oxidation of sulfides and oxidative coupling of thiols (using H₂O₂ as green oxidant), the products of which are obtained in high to excellent yields. The products can be separated by a simple extraction with organic solvent and the catalyst is highly efficient, especially in terms of selectivity of desired product. The catalytic system can be recycled and reused without significant loss of catalytic activity.     

An efficient ‘on-water’ synthesis of 1,4-dihydropyridines using Fe3O4@SiO2 nanoparticles as a reusable catalyst

An ‘on-water’, efficient, high yielding, expeditious method has been developed for the synthesis of 1,4-dihydropyridine (1,4-DHP) derivatives via an one-pot multi-component condensation of dimedone or 4-hydroxycoumarine, aldehydes, and ammonium acetate using Fe₃O₄@SiO₂ nanoparticles as a recyclable heterogeneous catalyst. This method takes advantage of the fact that water, a green solvent is used in combination with Fe₃O₄@SiO₂ nanoparticles as catalyst which can be easily recovered magnetically and reused for further runs.     

Magnetically recoverable lanthanum hydroxide as an efficient catalyst for Aerobic Oxidative Conversions of primary alcohols to the nitriles

Herein we report a novel magnetically recoverable lanthanum hydroxide nanoparticles for oxidative synthesis of nitriles directly from corresponding alcohols with ammonia as nitrogen source. The procedure for the preparation and characterization of La(OH)₃/Fe₃O₄ magnetic nanoparticles were investigated and the scope and generality of the method was explored for a series of structurally diverse primary alcohols with electron‐donating and electron‐withdrawing groups. The best result was observed when 5 mol% of La with respect to the benzyl alcohol was used at reflux condition under O₂ atmosphere. The La(OH)₃/Fe₃O₄ magnetic nanoparticles could be easily isolated from the reaction mixture with an external magnet and reused at least 5 times without significant loss in activity.     

Threonine stabilizer‐controlled well‐dispersed small palladium nanoparticles on modified magnetic nanocatalyst for Heck cross‐coupling process in water

We report the synthesis of magnetically separable Fe₃O₄@Silica‐Threonine‐Pd⁰ magnetic nanoparticles with a core–shell structure. After synthesis of Fe₃O₄@Silica, threonine as an efficient stabilizer/ligand was bonded to the surface of Fe₃O₄@Silica. Then, palladium nanoparticles were generated on the threonine‐modified catalyst. The threonine stabilizer helps to generate palladium nanoparticles of small size (less than 4 nm) with high dispersity and uniformity. Magnetically separable Fe₃O₄@Silica‐Threonine‐Pd⁰ nanocatalyst was fully characterized using various techniques. This nanocatalyst efficiently catalysed the Heck cross‐coupling reaction of a variety of substrates in water medium as a green, safe and inexpensive solvent at 80°C. The Fe₃O₄@Silica‐Threonine‐Pd⁰ catalyst was used for at least eight successful consecutive runs with palladium leaching of only 0.05%.