Copper immobilized onto polymer‐coated magnetic nanoparticles as recoverable catalyst for ‘click’ reaction

Copper supported on polymer‐coated magnetic nanoparticles was designed and synthesized as a separable heterogeneous catalyst. The catalyst was fully characterized using several techniques such as Fourier transform infrared and energy‐dispersive X‐ray spectroscopies, scanning and transmission electron microscopies, X‐ray diffraction, vibrating sample magnetometry, thermogravimetric analysis and inductively coupled plasma atomic emission spectrometry. All results showed that copper was successfully supported on the polymer‐coated magnetic nanoparticles. Also, results showed that the synthesized material can be used as an efficient catalyst for the preparation of a series of 1,4‐disubstituted 1,2,3‐triazoles from corresponding halides, alkynes and sodium azide. The catalyst can be easily isolated from the reaction solution by applying an external magnet and reused for nine runs without any significant loss of catalytic activity.     

Selective aqueous oxidation of alcohols catalyzed by copper (II) phthalocyanine nanoparticles

A new catalyst based on metallophthalocyanine nanoparticles has been synthesized and characterized by scanning electron microscopy (SEM). The aqueous oxidation of alcohols to the corresponding carbonyl compounds (aldehydes and ketones) has been studied using tetra-n-butyl-ammonium-peroxo-monosulfate (n-Bu₄NHSO₅) as an oxidant and a catalytic system consisting of copper (II) phthalocyanine nanoparticles in water. The highly selective oxidation gave excellent yields of related aldehydes or ketones without remarkable over-oxidation of the carboxylic acids. Organic co-solvents, surfactants, and co-catalysts were not used in this catalytic strategy. This strategy was green and time effective. The oxidant's by-product (TBAHSO₄) and catalyst can be efficiently recovered and reused several times without any significant change of catalytic activity.     

Palladium oxide nanoparticles supported on graphene oxide: A convenient heterogeneous catalyst for reduction of various carbonyl compounds using triethylsilane

Palladium oxide nanoparticles supported on graphene oxide ‐ triethylsilane was found to be an effective reductive system for a broad range of reduction processes, including the reduction of various carbonyl compounds such as aromatic aldehydes to their corresponding alcohols or methyl arene compounds, aromatic ketones to their respective alcohols or saturated compounds, aromatic acyl chlorides to their reduced compounds. The desired products were obtained in good to excellent yields under mild conditions. The heterogeneous environmentally friendly catalyst can be easily separated from the reaction mixture through a simple filtration, facilitating purification of the prepared compounds.     

Sulfonic acid supported on magnetic nanoparticle as an eco‐friendly,durable and robust catalyst for the synthesis of β‐amino carbonyl compounds through solvent free Mannich reaction

A simple, efficient and environmentally benign solid acid catalyst was prepared by anchoring a propyl sulfonic acid on the surface of silica‐coated magnetic nanoparticles by low cost precursors. The catalyst has been then engaged in the efficient β‐amino carbonyl compounds production via three component Mannich reaction under solvent free reaction condition at room temperature. After the completing the reaction, the catalyst was readily separated by external magnet and reused for 10 successive rounds of reaction, without any significant loss in catalytic efficiency. The solid acidic system presented reusable strategy for the efficient synthesis of β‐amino carbonyl compounds, simplicity in operation, and green aspects by avoiding toxic conventional catalysts under solvent‐free condition.     

Green bio‐based synthesis of Fe2O3@SiO2‐IL/Ag hollow spheres and their catalytic utility for ultrasonic‐assisted synthesis of propargylamines and benzo[b]furans

A novel magnetic hybrid system containing nano‐magnetic Fe₂O₃ hollow spheres, silica shell, [pmim]Cl ionic liquid and silver nanoparticles was synthesized and characterized. The silver nanoparticles were prepared via biosynthesis using Achillea millefolium flower as reducing and stabilizing agent. The hybrid system was successfully used as an efficient and reusable catalyst for promoting green ultrasonic‐assisted A³ and KA² coupling reactions as well as benzo[b]furan synthesis. It was found that decoration of the magnetic core with non‐magnetic moieties decreased the maximum saturation magnetization. However, the catalyst was still superparamagnetic and could be simply separated from the reaction mixture using an external magnet. The heterogeneous nature of the catalyst was also confirmed by studying its reusability and stability and the leaching of silver. Use of aqueous media, high yields, short reaction times, broad substrate tolerance and low required amount of catalyst are the merits of this protocol.     

Synthesis and characterization of a magnetically recoverable molybdenum(VI) nanocatalyst for eco-friendly oxidation of alcohols

A catalyst based on immobilization of a molybdenum(VI) Schiff base complex on γ-Fe₂O₃ magnetic nanoparticles has been synthesized and characterized. This catalyst was employed for the selective oxidation of alcohols to the corresponding carbonyl compounds in EtOH/H₂O₂. The catalyst can be easily separated from the reaction mixture by decantation using an external magnet and reused efficiently in five subsequent reaction cycles without any significant decrease in activity or selectivity.     

Oxidative esterification of methylarenes and 1,3‐dicarbonyls catalysed by copper chloride immobilized on magnetic nanoparticles

Superparamagnetic CuCl nanoparticles were prepared and identified as an effective heterogeneous catalyst for the tandem transformation of methylarenes and 1,3‐dicarbonyl compounds into the corresponding enole esters by the use of tert ‐butyl hydroperoxide as an external oxidant. The catalyst can be removed from the reaction medium simply by use of an external magnet. As a consequence, various derivatives of enol esters were synthesized in moderate to good yields.     

Catalytic reduction of 4‐nitrophenol using silver nanoparticles‐engineered poly(N‐isopropylacrylamide‐co‐acrylamide) hybrid microgels

Nearly monodisperse poly(N ‐isopropylacrylamide‐co ‐acrylamide) [P(NIPAM‐co‐AAm)] microgels were synthesized using precipitation polymerization in aqueous medium. These microgels were used as microreactors to fabricate silver nanoparticles by chemical reduction of silver ions inside the polymer network. The pure and hybrid microgels were characterized using Fourier transform infrared and UV–visible spectroscopies, dynamic light scattering, X‐ray diffraction, thermogravimetric analysis, differential scanning calorimetry and transmission electron microscopy. Results revealed that spherical silver nanoparticles having diameter of 10–20 nm were successfully fabricated in the poly(N ‐isopropylacrylamide‐co ‐acrylamide) microgels with hydrodynamic diameter of 250 ± 50 nm. The uniformly loaded silver nanoparticles were found to be stable for long time due to donor–acceptor interaction between amide groups of polymer network and silver nanoparticles. Catalytic activity of the hybrid system was tested by choosing the catalytic reduction of 4‐nitrophenol as a model reaction under various conditions of catalyst dose and concentration of NaBH₄ at room temperature in aqueous medium to explore the catalytic process. The progress of the reaction was monitored using UV–visible spectrophotometry. The pseudo first‐order kinetic model was employed to evaluate the apparent rate constant of the reaction. It was found that the apparent rate constant increased with increasing catalyst dose due to an increase of surface area as a result of an increase in the number of nanoparticles.     

Immobilization of copper ions onto α‐amidotriazole‐functionalized magnetic nanoparticles and their application in the synthesis of triazole derivatives in water

A new heterogeneous copper catalyst was synthesized by immobilization of copper ions onto magnetic nanoparticles with a new ligand based on triazole. The catalyst was characterized using scanning and transmission electron microscopies, atomic absorption and Fourier transform infrared spectroscopies, and thermogravimetric, elemental and energy‐dispersive X‐ray analyses. The results confirmed that a good level of organic groups was immobilized on the magnetic nanoparticles. Huisgen cycloaddition reaction was chosen as a model reaction for the investigation of catalyst activity under green conditions. Phenylacetylene and benzyl bromide derivatives were used for the synthesis of triazoles. The reaction proceeded with good to excellent yields for various alkynes and alkyl halides. To investigate catalyst activity for inactive alkynes, aliphatic alkynes were used in the model reaction. The corresponding triazoles were obtained in good to excellent yields and a high regioselectivity for products was obtained. The catalyst was easily separated using an external magnetic field and subsequently reused in ten reaction cycles without any loss of catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

Cu nanoparticles immobilized on modified magnetic zeolite for the synthesis of 1,2,3‐triazoles under ultrasonic conditions

Magnetically recoverable copper nanoparticle‐loaded natural zeolite (CuNPs/MZN) as an efficient catalyst was synthesized. The Fe₃O₄ magnetic nanoparticles were immobilized into the pores of natural clinoptilolite zeolite, which were modified with epichlorohydrine and ethylenediamine species and then CuNPs were decorated on the surface of functionalized zeolite (CuNPs/MZN). The catalysts were successfully characterized by Fourier transform‐infrared, CHN, thermogravimetric analysis, inductively coupled plasma, X‐ray diffraction, scanning electron microscopy and transmission electron microscopy techniques. The 1,2,3‐triazoles were readily synthesized through using the catalyst in high yields and short reaction times under ultrasonic conditions via CuAAC reactions of aryl azides and terminal alkynes. The CuNPs/MZN was easily separated from the reaction mixture by an external magnet and reused several times successfully. The catalyst could be used for the synthesis of various organic compounds.     

4‐OH‐TEMPO/TCQ/TBN/HCl: A Metal‐Free Catalytic System for Aerobic Oxidation of Alcohols under Mild Conditions

A green and economical catalyst system, 4‐OH‐TEMPO/TCQ/TBN/HCl, for the aerobic oxidation of a broad range of primary and secondary alcohols to the corresponding carbonyl compounds has been developed. These reactions proceed without transition‐metals under mild conditions with excellent yields.     

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.     

A manganese Schiff base complex immobilized on copper–ferrite magnetic nanoparticles as an efficient and recyclable nanocatalyst for selective oxidation of alcohols

A magnetically recoverable nanocatalyst was synthesized by covalent binding of a Schiff base ligand, namely N,N′-bis(Salicylidene)-1,3-diaminopropane-2-ol (H₂salpn), onto the surface of silica-coated magnetic CuFe₂O₄ nanoparticles, followed by complexation with MnCl₂. The resulting core–shell nanoparticles were characterized by spectroscopic and microscopic methods, including FTIR, XRD, VSM, TGA elemental analysis, TEM, and SEM. The Mn content was determined by ICP analysis. The nanoparticles were investigated as a catalyst for the selective oxidation of alcohols to the corresponding carbonyl compounds with tertiary-butyl hydrogen peroxide. The catalyst can be magnetically separated for reuse, with no noticeable loss of activity in subsequent reaction cycles. FTIR, VSM, and leaching experiments after three successive cycles confirmed that the catalyst was strongly anchored to the magnetic nanoparticles. A suitable mechanism for the reaction is proposed.     

Highly dispersed palladium nanoparticles on mesocellular foam: an efficient and recyclable heterogeneous catalyst for alcohol oxidation

Palladium nanoparticles immobilized on amino-functionalized mesocellular foam constitute an efficient catalyst for the aerobic oxidation of primary and secondary alcohols to their corresponding carbonyl compounds in high to excellent yields. An exceptionally high TON of 365?000 was reached for the oxidation of 1-phenylethanol under solvent-free reaction conditions. The catalyst can be recycled many times with retained activity as shown by the identical rate curves of the first and fifth runs.     

Chemo‐selective reduction of nitro and nitrile compounds using Ni nanoparticles immobilized on hyperbranched polymer‐functionalized magnetic nanoparticles

The nitro and nitrile groups in aromatic and aliphatic compounds containing various reducible substituents such as carboxylic acid, ketone, aldehyde and halogen are selectively reduced to the corresponding amines in water as a green solvent with excellent yields by employing NaBH₄ in the presence of Fe₃O₄@PAMAM/Ni(0)‐b‐PEG nanocatalyst. The morphology and structural features of the catalyst were characterized using various microscopic and spectroscopic techniques. The designed catalyst system because of it being covered with hydrophilic polymers is soluble in a wide range of solvents (e.g. water and ethanol) and suitable for immobilizing and stabilizing Ni nanoparticles in aqueous mediums. In addition, the catalyst can be easily recovered from a reaction mixture by applying an external magnetic field and can be reused up to six runs without significant loss of activity.     

Preparation of Fe3O4@5,10‐dihydropyrido[2,3‐b]quinoxaline‐7,8‐diol copper complex: A capable nanocatalyst for the green synthesis of 1‐substituted 1H‐tetrazoles

Fe₃O₄ magnetic nanoparticles functionalized with 5,10‐dihydropyrido[2,3‐b]quinoxaline‐7,8‐diol were synthesized as was their complex with copper as a novel nanomagnetic iron oxide catalyst via a simple and green method, and characterized using various techniques. The capability of the catalyst was evaluated in the one‐pot three‐component synthesis of different tetrazoles, which showed very good results. Mild reaction conditions, good reusability and simple magnetic work‐up make this methodology interesting for the efficient synthesis of tetrazoles.     

Iron oxide nanoparticles coated with green tea extract as a novel magnetite reductant and stabilizer sorbent for silver ions: Synthetic application of Fe3O4@green tea/Ag nanoparticles as magnetically separable and reusable nanocatalyst for reduction of 4‐nitrophenol

Green tea extract having many phenolic hydroxyl and carbonyl functional groups in its molecular framework can be used in the modification of Fe₃O₄ nanoparticles. Moreover, the feasibility of complexation of polyphenols with silver ions in aqueous solution can improve the surface properties and capacity of the Fe₃O₄@green tea extract nanoparticles (Fe₃O₄@GTE NPs) for sorption and reduction of silver ions. Therefore, the novel Fe₃O₄@GTE NPs nano‐sorbent has potential ability as both reducing and stabilizing agent for immobilization of silver nanoparticles to make a novel magnetic silver nanocatalyst (Fe₃O₄@GTE/Ag NPs). Inductively coupled plasma analysis, transmission and scanning electron microscopies, energy‐dispersive X‐ray and Fourier transform infrared spectroscopies, and vibrating sample magnetometry were used to characterize the catalyst. Fe₃O₄@GTE/Ag NPs shows high catalytic activity as a recyclable nanocatalyst for the reduction of 4‐nitrophenol at room temperature.     

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.     

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.     

Gold nanoparticles anchored onto the magnetic poly(ionic‐liquid) polymer as robust and recoverable catalyst for reduction of Nitroarenes

Gold nanoparticles supported on poly ionic‐liquid magnetic nanoparticles (MNP@PIL@Au) were synthesized by reduction of HAuCl4 with sodium borohydride. The synthesized catalyst was characterized using by AAS, TEM, FT‐IR, EDS, TGA and XRD techniques. The performance of the synthesized catalyst was investigated in the reduction of nitroarenes with NaBH₄. The reaction was carried out for various nitroarenes in water and mild conditions with high yields. The catalyst selectivity for the reduction of nitro group in the presences of other functional groups such as halides and alkynes was fairly well. The recycling of the catalyst was done 8 times without any significant loss of its catalytic activity.