Dendrimer‐encapsulated Cu(Π) nanoparticles immobilized on superparamagnetic Fe3O4@SiO2 nanoparticles as a novel recyclable catalyst for N‐arylation of nitrogen heterocycles and green synthesis of 5‐substituted 1H‐tetrazoles

In this study, dendrimer‐encapsulated Cu(Π) nanoparticles immobilized on superparamagnetic Fe₃O₄@SiO₂ nanoparticles were prepared via a multistep‐synthesis. Then, the synthesized composite was fully characterized by various techniques such as fourier transform infrared (FT‐IR) spectroscopy, X‐ray diffraction (XRD), dynamic light scattering (DLS), UV‐vis spectroscopy, energy dispersive X‐ray analysis (EDX), thermogravimetric analysis (TGA) and vibration sample magnetometer (VSM). From the information gained by FE‐SEM and TEM studies it can be inferred that the particles are mostly spherical in shape and have an average size of 50 nm. Also, the amount of Cu is determined to be 0.51 mmol/g in the catalyst by inductively coupled plasma (ICP) analyzer. This magnetic nano‐compound has been successfully applied as a highly efficient, magnetically recoverable and stable catalyst for N‐arylation of nitrogen heterocycles with aryl halides (I, Br) and arylboronic acids without using external ligands or additives. The catalyst was also employed in a one‐pot, three‐component reaction for the efficient and green synthesis of 5‐substituted 1H‐tetrazoles using various aldehydes, hydroxylamine hydrochloride and sodium azide in water. The magnetic catalyst can be easily separated by an external magnet bar and is recycled seven times without significant loss of its activity.     

Green chemistry multicomponent protocol for formylation and Knoevenagel condensation for synthesis of (Z)-5-arylaminomethylene pyrimidine 2, 4, 6-trione derivatives in water

A green, efficient, and novel one-pot multicomponent protocol was developed to achieve stereoselective (Z)-5-(arylpropenylidine)-2,4,6-pyrimidinetrione derivatives using a three-component reaction involving appropriate aromatic amines, formic acid, and barbituric acid using water as green solvent by conventional thermal heating process. In this way, N-formylation of various amines takes place. The resulted different formamides undergo Knoevenagel condensation with active methylene group containing compound, that is, barbituric acid. The newly synthesized compounds were characterized by spectral analysis (Fourier Transform Infrared [FT-IR], 1H nuclear magnetic resonance [NMR], 13C NMR, Heteronuclear Multiple-Bond Correlation [HMBC], Mass, UV spectroscopy) and elemental analysis. The multicomponent reactions (MCRs) showed good stereoselectivity.     

Bis(4‐pyridylamino)triazine‐stabilized magnetite nanoparticles: preparation,characterization and application as a retrievable catalyst for the green synthesis of 4H‐pyran, 4H‐thiopyran and 1,4‐dihydropyridine derivatives

Synthesis of bis(4‐pyridylamino)triazine stabilized on silica‐coated nano‐Fe₃O₄ particles, and their feasibility as a reusable heterogeneous basic catalyst are reported. The catalytic performance of this novel material was studied for the green synthesis of highly functionalized 4H ‐pyran, 4H ‐thiopyran and 1,4‐dihydropyridine derivatives via one‐pot multicomponent reactions. Eco‐friendly method, high yield and purity of desired products, short reaction time along with ease of workup procedure outline the advantages of these new methodologies over earlier ones. Surface and magnetic properties of the core–shell hybrid nanoparticles were characterized via transmission and scanning electron microscopies, X‐ray diffraction, energy‐dispersive X‐ray and Fourier transform infrared spectroscopies and vibrating sample magnetometry. Copyright © 2016 John Wiley & Sons, Ltd.     

Green synthesis of supported palladium nanoparticles employing pine needles as reducing agent and carrier: New reusable heterogeneous catalyst in the Suzuki coupling reaction

A green method for the synthesis of supported Pd nanoparticles (NPs) using pine needle extract as the reducing agent and the extracted residue of pine needle (RPN) as the carrier is described. The Pd/RPN nanocomposites were characterized using Fourier transform infrared, UV–visible, inductively coupled plasma atomic emission and X‐ray photoelectron spectroscopies, transmission electron microscopy and X‐ray diffraction. The spherical Pd NPs had a mean particle size of 3.25 nm and were evenly distributed on the RPN surface. More importantly, the Pd/RPN nanocomposite, as a heterogeneous catalyst, presented superior catalytic activity for the Suzuki coupling reaction. The yield of the reaction of 4‐bromotoluene with phenylboronic acid catalyzed by Pd_0.03/RPN reached 98% with low Pd loading (0.1 mmol%) at room temperature for 30 min. In addition, the catalyst could be easily separated by centrifugation and reused at least six times without significant loss of activity.     

Cyclodextrin‐supported palladium complex: A highly active and recoverable catalyst for Suzuki–Miyaura cross‐coupling reaction in aqueous medium

A water‐soluble, cyclodextrin‐supported palladium complex (DACH‐Pd‐β‐CD) catalytic system was designed and synthesized, which can efficiently catalyze Suzuki–Miyaura cross‐coupling reactions between aryl halides and arylboronic acid in water under mild conditions. The catalyst was successfully characterized using the methods of transmission electron microscopy, energy‐dispersive X‐ray spectrometry, X‐ray diffraction, thermogravimetric analysis, and Fourier transform infrared and NMR spectroscopies. Furthermore, the catalyst can be easily separated from the reaction mixture and still maintain high catalytic activity after ten cycles. No leaching of palladium into the reaction solution occurred. The advantages of green solvent (water), short reaction times (2–6 h), low catalyst loading (0.001 mol%), excellent yields (up to 99%) and reusability of the catalyst mean it will have potential applications in green chemical synthesis.     

Greener approach for synthesis of monodispersed palladium nanoparticles using aqueous extract of green tea and their catalytic activity for the Suzuki–Miyaura coupling reaction and the reduction of nitroarenes

A facile and green route for the synthesis of palladium nanoparticles (NPs) was developed utilizing non‐toxic and renewable natural green tea extract as the reducing, stabilizing and capping agent. The as‐prepared Pd‐NPs@G.Tea extract was characterized using UV–visible spectroscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, field‐emission scanning electron microscopy, transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. The Pd‐NPs@G.Tea extract could be used as an efficient and heterogeneous catalyst for Suzuki coupling reactions between phenylboronic acid and a range of aryl halides containing iodo, bromo and chloro moieties, and also for the reduction of nitroarenes using sodium borohydride in an environmentally friendly medium. Excellent yields of products were obtained with a wide range of substrates and the catalyst was recycled multiple times without any significant loss of its catalytic activity.     

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.     

Preparation and characterization of copper chloride supported on citric acid‐modified magnetite nanoparticles (Cu2+‐CA@Fe3O4) and evaluation of its catalytic activity in the reduction of nitroarene compounds

A new, powerful and recyclable copper catalyst were prepared by heterogenization of copper chloride using of Fe₃O₄ nano particles modified with citric acid as a linker. This system can catalyze reduction of nitroaren compound to aniline derivatives in the presence of Sodium borohydride as a reduction agent in moderate to good yields. In addition, easy separation and recoverable with an external permanent magnet is the dominant properties of this catalyst (Cu²⁺‐CA@Fe₃O₄).     

Microwave‐Assisted One‐Pot Preparation of Tetrahydro‐β‐carboline Hydrochlorides under Solvent‐Free Conditions

An efficient and environmentally friendly synthesis of tetrahydro‐β‐carboline hydrochlorides via Pictet–Spengler reaction was described. Tryptamine hydrochlorides were used as the reactant and no additional acid catalyst was needed. This reaction was completed within 2.5–9 min in good yield.     

An Efficient Four‐component Synthesis of Spiro[indoline‐pyrazolo[4′,3′:5,6]pyrido[2,3‐d]pyrimidine]triones

A four‐component reaction in the presence of Alum [KAl(SO₄)₂·12H₂O] as an inexpensive and reusable catalyst using the ionic liquid as an effective green reaction media is reported.