Cu(II) Schiff base complex supported on Fe3O4 nanoparticles as an efficient nanocatalyst for the selective aerobic oxidation of alcohols

Herein, we have prepared a new Cu(II) Schiff base complex supported onto the surface of modified Fe₃O₄ nanoparticles as highly stable, heterogeneous and magnetically recyclable nanocatalyst for the selective aerobic oxidation of different alcohols. The structure, morphology, chemical composition and magnetic property of the nanocatalyst and its precursors were characterized using FT‐IR, TGA, AAS, ICP‐AES, XRD, SEM, EDS, VSM and N₂ adsorption–desorption analyses. Characterization results exhibited the uniform spherical morphology for nanocatalyst and its precursors. A promising eco‐friendly method with short reaction time and high conversion and selectivity for oxidation of various primary and secondary alcohols under O₂ atmosphere condition was achieved. The synthesized nanocatalyst could be recovered easily by applying an external magnetic field and reused for least eight subsequent reaction cycles with only negligible deterioration in catalytic performance.     

Anchoring of Cu (II)-Schiff base complex on magnetic mesoporous silica nanoparticles: catalytic efficacy in one-pot synthesis of 5-substituted-1H-tetrazoles,antibacterial activity evaluation and immobilization of α-amylase

Magnetic mesoporous silica nanocomposite, Fe₃O₄@MCM-41, was prepared and functionalized with N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPS). Then Schiff base grafted nanoparticles were synthesized by the condensation of 5,5'-methylene bis (salicylaldehyde) and then benzhydrazide with Fe₃O₄@MCM-41-AEAPS. Finally, by adding Cu (CH₃COOH)₂.H₂O, the magnetic nanoparticles (MNPs) functionalized with Cu (II) Schiff base complex were synthesized. The new organic–inorganic hybrid nanocomposite was characterized by FT-IR, PXRD, AAS, BET, TGA, VSM, FE-SEM, HRTEM and EDX techniques. Then, the performance of this copper based magnetic nanocatalyst was investigated for the synthesis of 5-substituted 1H-tetrazole derivatives using one pot three-component reactions of various aldehydes, hydroxyl amine hydrochloride and sodium azide. The catalyst can be easily isolated from the reaction mixture by applying an external magnet and reused for at least 5 times without significant loss in catalytic activity. Also, the antibacterial activity of the streptomycin loaded magnetic nanoparticles against Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria in the presence and absence of a magnetic field were studied. Results revealed that when these materials exposed to the magnetic field, bacteriostatic activity of nanocomposites was increased. Furthermore, the enzyme immobilization ability of the synthesized compounds was investigated and the results showed that these nanoparticles efficiently immobilized amylase enzyme.     

Schiff base complex of Mo supported on iron oxide magnetic nanoparticles (Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>) as recoverable nanocatalyst for the selective oxidation of sulfides

In this work, a new tridentate Schiff base dioxo-molybdenum(VI) complex immobilized on silica-coated magnetic nanoparticles (MoO₂5CML–Fe₃O₄@SiO₂) has been synthesized and characterized using different techniques such as FTIR, TGA, AAS, ICP–AES, XRD, VSM, EDX and SEM analyses. The catalytic activity of synthesized complex was examined in the oxidation of various sulfides in the presence of H₂O₂ as cheap, green and eco-friendly oxidant. This catalytic system provides high conversion and selectivity toward either sulfoxides or sulfones under different conditions. Also, the nanocatalyst could be easily separated and regenerated from reaction media by external magnet and could be reused for ten times without significant loss of the activity and selectivity.     

Cu (II)‐β‐cyclodextrin complex stabilized on magnetic nanoparticles: A retrievable hybrid promoter for green synthesis of spiropyrans

The magnetic core of manganese ferrite (MnFe₂O₄) nanoparticles has a significant stability in comparison with ferrite (Fe₃O₄) nanoparticles. The unique supramolecular properties of β‐cyclodextrin (β‐CD), such as hydrophobic cavity, hydrophilic exterior and ‐OH functional groups, make it a good candidate for functionalization and catalytic application. So, a surface‐modified magnetic solid support with the Cu (II)‐β‐CD complex was prepared. The structure of nanoparticles was characterized by Fourier transform‐infrared spectroscopy, X‐ray powder diffraction, thermogravimetric analysis, vibrating‐sample magnetometry, inductively coupled plasma‐optical emission spectrometry and scanning electron microscope analyses. The catalytic activity of these nanoparticles was investigated in the synthesis of spiropyrans and high yields of desired products obtained under green media. Some advantages of this novel catalyst for this reaction are high yields, short reaction times, green solvent and conditions, easy workup procedure, negligible copper leaching, reusability without a significant diminish in catalytic efficiency, and simple separation of nanocatalyst by using an external magnet alongside the environmental compatibility and sustainability.     

An easy synthesis of nanostructured magnetite-loaded functionalized carbon spheres and cobalt ferrite

An easy method in a solvothermal system has been developed to synthesize nanostructured magnetite (Fe₃O₄)-loaded functionalized carbon spheres (CSs) and cobalt ferrite (CoFe₂O₄). Surface-tunable CSs loaded with iron oxide (Fe₃O₄) nanoparticles were prepared using an acetylferrocene Schiff base (OPF), whereas spinel cobalt ferrite (CoFe₂O₄) was synthesized via metal complexes of a ferrocenyl Schiff base with phenol moiety (Co-OPF). The formed composite powder was investigated using X-ray powder diffraction, Raman spectrometry, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and vibrating sample magnetometry. It was found that most of the iron oxide nanoparticles were evenly distributed upon the surface of the CSs. Furthermore, the surface of the iron oxide-loaded CSs has large numbers of functional groups. Good saturation magnetization was achieved for the formed magnetic nanoparticles.     

Synthesis,characterization, and catalytic activity of supported molybdenum Schiff base complex as a magnetically recoverable nanocatalyst in epoxidation reaction

A heterogeneous nanocatalyst was prepared via covalent anchoring of dioxomolybdenum(VI) Schiff base complex on core–shell structured Fe₃O₄@SiO₂. The properties and the nature of the surface-fixed complex have been identified by a series of characterization techniques such as SEM, EDX, XRD, TGA, FT-IR, and VSM. The synthesized hybrid material was an efficient nanocatalyst for selective oxidation of olefins to corresponding epoxides with t-BuOOH in high yields and selectivity. The catalyst could be conveniently recovered by applying an external magnetic field and reused several times without significant loss of efficiency.     

Schiff base complex of palladium immobilized on magnetic nanoparticles: an efficient and recyclable nanocatalyst for CC coupling reactions

A Schiff base complex of palladium anchored on Fe₃O₄ magnetic nanoparticles as an efficient and magnetically reusable nanocatalyst is reported for C? C bond formation through Heck and Suzuki reactions. The catalyst was easily recovered and reused several times without significant loss of its catalytic efficiency or palladium leaching. The magnetic nanocatalyst was characterized using Fourier transform infrared and inductively coupled plasma atomic emission spectroscopies, thermogravimetric analysis, vibrating sample magnetometry, and transmission and scanning electron microscopies. Copyright © 2016 John Wiley & Sons, Ltd.     

Copper Schiff base complex immobilized on magnetic graphene oxide: Efficient heterogeneous nanocatalyst for treating environmental pollutants and synthesis of chromenes

Herein, a new Cu(II) Schiff base complex was immobilized onto the magnetic graphene oxide surface through a stepwise procedure. The as-synthesized nanostructure (GO/Fe₃O₄/CuL) was characterized by various techniques including Fourier transform infrared (FT-IR), Raman spectroscopies, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), energy-dispersive X-ray (EDX) and inductively coupled plasma (ICP) spectroscopies, N₂ adsorption–desorption analysis, vibrating sample magnetometry (VSM), and X-ray diffraction (XRD). The catalytic activity of the synthesized nanocatalyst was examined in 4-nitrophenol (4-NP), Congo red (CR), and methylene blue (MB) reduction using NaBH₄ in an aqueous solution at room temperature. The reaction progress was monitored by UV–Vis spectroscopy. Also, the synthesized nanostructure was evaluated as an efficient catalyst for the synthesis of 2-amino-4H-benzopyrans via three-component reactions of 1-naphthol, malononitrile, and various aldehydes in ethanol/water at 50°C. The use of green solvents, the short reaction time, the high product yield, and easy separation from the reaction environment are the main benefits of this catalytic system. By covalent grafting of the complex on the graphene oxide surface, its catalytic performance significantly increased compared with graphene oxide; this is probably related to the chemical change of the graphene oxide surface. The results show the high chemical stability and the improved reusability of the synthesized nanocatalyst (six times) without significant loss in the catalytic activity of GO/Fe₃O₄/CuL nanocomposite.     

Palladium nanoparticles immobilized on Schiff base‐functionalized mesoporous silica as a highly efficient and magnetically recoverable nanocatalyst for Heck coupling reaction

A new magnetically recoverable nanocatalyst was prepared by functionalization of mesoporous silica (SBA‐15) with a Schiff base ligand, and then immobilization of palladium nanoparticles on it using a simple procedure. This heterogeneous catalyst was fully characterized using appropriate analyses and its catalytic efficiency was investigated in Heck reaction using iodo‐, bromo‐ and chlorobenzene derivatives and styrene, with the aim of synthesizing stilbene derivatives, a class of compounds with a variety of pharmacological properties. Some of the characteristics of this nanocatalyst include good dispersion of palladium nanoparticles on the SBA‐15 support, easy separation, catalyses the production of stilbene derivatives in a short time with excellent yields even for bromo‐ and chlorobenzene, and preservation of its catalytic activity after eight reaction cycles.     

Heterogenization of a molybdenum Schiff base complex as a magnetic nanocatalyst: An eco-friendly,efficient, selective and recyclable nanocatalyst for the oxidation of alkenes

A Schiff base ligand derived from 5-bromo-2-hydroxybenzaldehyde and 2,2′-dimethylpropylenediamine (H₂L) and its corresponding dioxomolybdenum(VI) complex (Mo(O)₂L) has been synthesized and characterized by spectroscopic methods. The adsorption of Mo(O)₂L on the surface of silica-coated magnetite nanoparticles via hydrogen bonding led to the formation of (α-Fe₂O₃)–MCM-41–Mo(O)₂L as a heterogeneous catalyst. FT-IR and atomic absorption spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize and investigate the new nanocatalyst. A practical catalytic method for the efficient and highly selective oxidation of a wide range of olefins with hydrogen peroxide and tert-butyl hydroperoxide in ethanol over the prepared molybdenum nanocatalyst was investigated. Under reflux conditions, the oxidation of cyclooctene with tert-butyl hydroperoxide or hydrogen peroxide led to the formation of epoxide as the sole product. The catalyst was reused at least six times without a significant decrease in catalytic activity or selectivity, and without detectable leaching of the catalyst.     

The solvent‐free synthesis of polysubstituted pyrroles by a reusable copper Schiff base complex immobilized on silica coated Fe3O4, and DNA binding study of one resulting derivative as a potential anticancer drug

We demonstrate herein the synthesis of a new copper Schiff base complex immobilized on silica‐coated Fe₃O₄ nanoparticles. The structure and composition of this magnetic nanocatalyst were analyzed using Fourier transform infrared (FT‐IR), X‐ray powder diffraction (XRD), vibrating sample magnetometry (VSM), scanning electron microscopy (SEM), energy dispersive X‐ray (EDX) and inductively coupled plasma atomic emission spectroscopy (ICP‐AES). This nanocomposite was found to be an efficient nanocatalyst for the synthesis of polysubstituted pyrrole derivatives and the products were isolated with high turnover number (TON) and high to excellent yields. Among the new synthesized polysubstituted pyrrole derivatives, we explored the first computational and experimental binding study of methyl 1‐benzyl‐4‐(furan‐2‐yl)‐2‐methyl‐1H‐pyrrole‐3‐carboxylate (SP‐10) with calf thymus deoxyribonucleic acid (ct‐DNA), suggesting their application as potential anticancer activity. In addition, the binding modes of SP‐10 with DNA and human serum albumin (HSA) were verified by molecular docking technique.     

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.     

Covalent supporting of novel dioxo‐molybdenum tetradentate pyrrole‐imine complex on Fe3O4 as high‐efficiency nanocatalyst for selective epoxidation of olefins

A novel Mo(VI) tetradentate Schiff base complex based on two pyrrole‐imine donors was anchored covalently on Fe₃O₄ nanoparticles and characterized using physicochemical techniques. The catalytic epoxidation process was optimized in terms of the effects of solvent, reaction temperature, kind of oxidant and amount of oxidant and catalyst. Then the novel heterogeneous nanocatalyst was used for the efficient and selective catalytic epoxidation of internal alkenes (cyclohexene, cyclooctene, α‐pinene, indene and trans ‐1,2‐diphenylethene) and terminal alkenes (n ‐heptene, n ‐octene, n ‐dodecene and styrene) using tert ‐butyl hydroperoxide (70% in water) as oxidant in 1,2‐dichloroethane as solvent. The prepared nanocatalyst is very effective for the selective epoxidation of cis ‐cyclooctene with 100% conversion, 100% selectivity and turnover frequency of 1098 h⁻¹ in just 30 min. The magnetic nanocatalyst was easily recovered using an external magnetic field and was used subsequently at least six times without significant decrease in conversion.     

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 choline chloride–urea deep eutectic solvent‐modified magnetic nanoparticles for synthesis of various 2‐amino‐4H‐pyran derivatives in water solution

A novel hybrid magnetic nanocatalyst was synthesized by covalent coating of Fe₃O₄ magnetic nanoparticles with choline chloride–urea deep eutectic solvent using 3‐iodopropyltrimethoxysilane as a linker. The structure of this new catalyst was fully characterized via elemental analysis, transmission and scanning electron microscopies, X‐ray diffraction and Fourier transform infrared spectroscopy. It was employed in the synthesis of various 2‐amino‐4H ‐pyran derivatives in water solution via an easy and green procedure. The desired products were obtained in high yields via a three‐component reaction between aromatic aldehyde, enolizable carbonyl and malononitrile at room temperature. The employed nanocatalyst was easily recovered using a magnetic field and reused four times (in subsequent runs) with less than 8% decrease in its catalytic activity.     

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.     

Synthesis and application of novel 1,2,3‐triazolylferrocene‐containing ionic liquid supported on Fe3O4 nanocatalyst in the synthesis of new pyran‐substituted Betti bases

A novel magnetic ferrocene‐labelled ionic liquid based on triazolium, [Fe₃O₄@SiO₂@Triazol‐Fc][HCO₃], has been synthesized and has been successfully introduced as a recyclable heterogeneous nanocatalyst. The catalytic activity of the novel magnetic nanoparticles was evaluated in the one‐pot three‐component synthesis of a wide variety of Betti bases. A simple, facile and highly efficient green method has been developed for the synthesis of kojic acid‐containing Betti base derivatives at room temperature. Additionally, this new protocol has notable advantages such as short reaction times, green reaction conditions, high yields and simple workup and purification steps. Also, the novel nanocatalyst could be easily recovered using an external magnetic field and reused for six consecutive reaction cycles without significant loss of activity. The newly synthesized nanocatalyst was characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, energy‐dispersive X‐ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy and Brunauer–Emmett–Teller measurements.     

A molybdenum(VI) Schiff base complex immobilized on functionalized Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles as a recoverable nanocatalyst for synthesis of 2-amino-4<Emphasis Type="Italic">H</Emphasis>-benzo[<Emphasis Type="Italic">h</Emphasis>]chromenes

A dioxomolybdenum(VI) complex of a Schiff base, immobilized on the surface of modified Fe₃O₄ with a silica coating, has been synthesized and characterized by spectroscopic and microscopic techniques including FTIR, TGA, ICP, SEM, EDX, VSM, and XRD analyses. The catalytic performance of this material has been evaluated for the preparation of 2-amino-4H-benzo[h]chromenes via the one-pot, three-component reaction of aldehydes, malononitrile, and 1-naphthol under solvent-free conditions. The benefits of this protocol are short reaction time, simple workup procedure, and high yields of products. Also, the synthesized nanocatalyst could be separated easily from the reaction mixture using an external magnet and reused for four consecutive times with only minor degradation of its catalytic performance.     

Synthesis and characterization of Fe3O4@SiO2–polymer-imid–Pd magnetic porous nanospheres and their application as a novel recyclable catalyst for Sonogashira–Hagihara coupling reactions

We demonstrate herein the modification of magnetic nanoparticles and their use as a magnetic nanocatalyst in direct coupling reactions of aryl halides with terminal alkynes. Magnetite particles were prepared by simple co-precipitation method in aqueous medium, and then Fe₃O₄@ SiO₂ nanosphere was synthesized by using nano-Fe₃O₄ as the core, TEOS as the silica source and PVA as the surfactant. Fe₃O₄@SiO₂ was coated with polymeric N-heterocyclic carbene/Pd. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, field emission scanning electron microscopy, dynamic light scattering, thermogravimetric analysis, vibration sample magnetometer and N₂ adsorption–desorption isotherm analysis. Poly (N-vinyl imidazole) functionalized Fe₃O₄@SiO₂ nanoparticle was found to be an efficient nanocatalyst in Sonogashira–Hagihara cross-coupling reactions. The nanocatalyst can be easily recovered by a magnetic field and reused for six runs without appreciable loss of its catalytic activity.