Pd‐SBT@MCM‐41: As an efficient,stable and recyclable organometallic catalyst for C‐C coupling reactions and synthesis of 5‐substituted tetrazoles

A palladium S‐benzylisothiourea complex was anchored on functionalized MCM‐41 (Pd‐SBT@MCM‐41) and applied as efficient and reusable catalyst for the synthesis of 5‐substituted 1H –tetrazoles using [2 + 3] cycloaddition reaction of various organic nitriles with sodium azide (NaN₃) in poly(ethylene glycol) (PEG) as green solvent. Also this catalyst was applied as an versatile organometallic catalyst for Suzuki cross‐coupling reaction of aryl halides and phenylboronic acid (PhB(OH)₂) or sodium tetraphenyl borate (NaB(Ph)₄). This nanocatalyst was characterized by thermal gravimetric analysis (TGA), X‐ray Diffraction (XRD), scanning electron microscopy (SEM), inductively Coupled Plasma (ICP) and N₂ adsorption–desorption isotherms techniques. Recovery of the catalyst is easily achieved by centrifugation for several consecutive runs.     

One‐pot synthesis of 1‐ and 5‐substituted 1H‐tetrazoles using 1,4‐dihydroxyanthraquinone–copper(II) supported on superparamagnetic Fe3O4@SiO2 magnetic porous nanospheres as a recyclable catalyst

An effective one‐pot, convenient process for the synthesis of 1‐ and 5‐substituted 1H‐tetrazoles from nitriles and amines is described using1,4‐dihydroxyanthraquinone–copper(II) supported on Fe₃O₄@SiO₂ magnetic porous nanospheres as a novel recyclable catalyst. The application of this catalyst allows the synthesis of a variety of tetrazoles in good to excellent yields. The preparation of the magnetic nanocatalyst with core–shell structure is presented by using nano‐Fe₃O₄ as the core, tetraethoxysilane as the silica source and poly(vinyl alcohol) as the surfactant, and then Fe₃O₄@SiO₂ was coated with 1,4‐dihydroxyanthraquinone–copper(II) nanoparticles. The new catalyst was characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, dynamic light scattering, thermogravimetric analysis, vibration sample magnetometry, X‐ray photoelectron spectroscopy, nitrogen adsorption–desorption isotherm analysis and inductively coupled plasma analysis. This new procedure offers several advantages such as short reaction times, excellent yields, operational simplicity, practicability and applicability to various substrates and absence of any tedious workup or purification. In addition, the excellent catalytic performance, thermal stability and separation of the catalyst make it a good heterogeneous system and a useful alternative to other heterogeneous catalysts. Also, the catalyst could be magnetically separated and reused six times without significant loss of catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

HAp‐encapsulated γ‐Fe2O3‐supported dual acidic heterogeneous catalyst for highly efficient one‐pot synthesis of benzoxanthenones and 3‐pyranylindoles

A novel method is reported for the synthesis of benzoxanthenone and 3‐pyranylindole derivatives via one‐pot three‐component reactions using a newly synthesized HAp‐encapsulated γ‐Fe₂O₃‐supported dual acidic heterogeneous catalyst, as a reusable and highly efficient nanocatalyst. In this protocol the use of the nanocatalyst provided a green, useful and rapid method to generate products in short reaction times (4–20 min) and in excellent yields (87–96%). The paramagnetic nature of the catalyst provided a simple, trouble‐free and facile approach for the separation of the catalyst by applying an external magnet, and it could be used in eight cycles without significant loss in catalytic efficiency.     

Fe3O4@SiO2@sulfated boric acid as superparamagnetic and recyclable nanocatalyst‐assisted,one‐pot,pseudo four‐component synthesis of 5‐amino‐2‐aryl‐3H‐chromeno[4,3,2‐de][1,6]naphthyridine‐4‐carbonitrile derivatives

The catalytic performance of the superparamagnetic nanocatalyst Fe₃O₄@SiO₂@Sulfated boric acid as a green, recyclable, and acidic solid catalyst in the synthesis of chromeno[4,3,2‐de][1,6]naphthyridine derivatives has been studied. Chromeno[4,3,2‐de][1,6]naphthyridine derivatives via a pseudo four‐component reaction from aromatic aldehydes (1 mmol), malononitrile (2 mmol), and 2′‐hydroxyacetophenone in the presence of Fe₃O₄@SiO₂@Sulfated boric acid (0.004 g) as a nanocatalyst in 3 mL of water as a green solvent at 80°C has been synthesized. The advantages of this method are higher product yields in shorter reaction times, easy recyclability and reusability of the catalyst, and easy work‐up procedures. The nanocatalyst was reused at least six times. The nanocatalyst retained its stability in the reaction, and after reusability, it was separated easily from the reaction by an external magnet.     

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.     

Enantioselective synthesis of 3‐amino‐1‐aryl‐1H‐benzo[f]chromene‐2‐carbonitrile derivatives by Fe3O4@PS‐arginine as an efficient chiral magnetic nanocatalyst

A novel chiral magnetic nanocatalyst was prepared by the surface modification of Fe₃O₄ magnetic nanoparticles (MNPs) with a chloropropylsilane and further by arginine to form Fe₃O₄@propylsilan‐arginine (Fe₃O₄@PS‐Arg). After the structural confirmation of Fe₃O₄@PS‐Arg synthesized MNPs by Fourier transform‐infrared, X‐ray diffraction, field emission‐scanning electron microscopy, transmission electron microscopy, vibrating‐sample magnetometry and thermogravimetric analyses, their catalytic activity was evaluated for one‐pot enantioselective synthesis of 3‐amino‐1‐aryl‐1H‐benzo[f]chromene‐2‐carbonitrile derivatives. The results showed that in the presence of 0.07 g Fe₃O₄@PS‐Arg nanocatalyst and ethanol as solvent, the best reaction yield (96%) was obtained in the least time (5 min). Easy operation, reusability and stability, short reaction time, high reaction yields and good enantioselectivity are the major advantages of the newly synthesized nanocatalyst. Also, this study provides a novel strategy for further research and investigation on the synthesis of new reusable enantioselective catalysts and chiral compounds.     

(3‐Oxo‐[1,2,4]triazolidin‐1‐yl)bis (butane‐1‐sulfonic acid) functionalized magnetic γ‐Fe2O3 nanoparticles: A novel and heterogeneous nanocatalyst for one‐pot and efficient four‐component synthesis of novel spiro[indeno[1,2‐b]quinoxaline derivatives

The efficient synthesis of novel spiro[indeno[1,2‐b]quinoxaline derivatives via the four‐component condensation of amines, ninhydrin, isatoic anhydride, and о‐phenylenediamine derivatives catalyzed by ( 3‐oxo‐[1,2,4]triazolidin‐1‐yl)bis (butane‐1‐sulfonic acid) supported on γ‐Fe₂O₃ as novel heterogenous magnetic nanocatalyst was described. The novel nanocatalyst was characterized by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR), vibrating sample magnetometry (VSM), Field Emission Scanning Electron Microscopy (FE‐SEM), and thermal analysis (TGA‐DTG). The nanoparticles covered by (3‐oxo‐[1,2,4]triazolidin‐1‐yl)bis (butane‐1‐sulfonic acid) showed enhanced catalytic performance in the preparation of spiro[indeno[1,2‐b]quinoxaline derivatives in excellent yields. Moreover, this method showed several advantages such as mild conditions, high yields, easy work‐up, and being environmentally friendly. The catalyst can be easily separated from the reaction mixture by an external magnet, recycled, and reused several times without a noticeable decrease in catalytic activity.     

Isatin‐SO3H coated on amino propyl modified magnetic nanoparticles (Fe3O4@APTES@isatin‐SO3H) as a recyclable magnetic nanoparticle for the simple and rapid synthesis of pyrano[2,3‐d] pyrimidines derivatives

Isatin‐SO₃H coated on amino propyl modified magnetic nanoparticles (Fe₃O₄@APTES@isatin‐SO₃H) is found to be a novel, efficient, and reusable magnetic nanocatalyst, and characterized by FT‐IR, SEM, TEM, XRD, EDX, VSM, and TGA analysis. The magnetic nanocatalyst demonstrated outstanding performance in synthesis of pyrano[2,3‐d] pyrimidines derivatives via one‐pot three‐component reaction of various aromatic aldehydes 1, malononitrile 2, and barbituric acid 3 under reflux conditions in mixture of H₂O:EtOH (1:1) as solvent. Easy workup procedure, short reaction time, high yield, simple preparation and easy recovery of the catalyst, mild reaction conditions are some advantages of this work.     

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.     

Anchoring of Cu(II)–vanillin Schiff base complex on MCM‐41: A highly efficient and recyclable catalyst for synthesis of sulfides and 5‐substituted 1H–tetrazoles and oxidation of sulfides to sulfoxides

A copper(II)–vanillin complex was immobilized onto MCM‐41 nanostructure and was used as an inexpensive, non‐toxic and heterogeneous catalyst in the synthesis of symmetric aryl sulfides by the cross‐coupling of aromatic halides with S₈ as an effective sulfur source, in the oxidation of sulfides to sulfoxides using 30% H₂O₂ as a green oxidant and in the synthesis of 5‐substituted 1H –tetrazoles from a smooth (3 + 2) cycloaddition of organic nitriles with sodium azide (NaN₃). The products were obtained in good to excellent yields. This catalyst could be reused several times without loss of activity. Characterization of the catalyst was performed using Fourier transform infrared, energy‐dispersive X‐ray and atomic absorption spectroscopies, X‐ray diffraction, thermogravimetric analysis, and scanning and transmission electron microscopies.     

Equisetum arvense As an abundant source of silica nanoparticles. SiO2/H3PW12O40 nanohybrid material as an efficient and environmental benign catalyst in the synthesis of 2‐amino‐4H‐chromenes under solvent‐free conditions

Uniform SiO₂ nanoparticles were successfully prepared from Equisetum arvense obtained from the north‐east of Iran. Then, surface modification of the extracted nanoparticles was performed with a methanol solution of H₃PW₁₂O₄₀ via wet impregnation method. The prepared nanocatalyst was characterized by XRD, FESEM, ICP, UV–Vis, and FT‐IR spectroscopy. The supported heterogeneous nanocatalyst was successfully applied as a Lewis/Bronsted acid catalyst in the synthesis of a series of substituted 4H–chromenes via condensation of aromatic aldehydes, malononitrile, and 4‐hydroxycoumarin under solventless conditions with fine yields in appropriately short times.     

Catalytic Synthesis of 5‐Substituted Tetrazoles: Unexpected Reactions and Products

Tetrazoles are incredibly useful organic molecules with a wide range of applications from medicinal chemistry as carboxylic acid isosteres to high energy density materials in space research. In an effort to develop an easy protocol for the synthesis of tetrazoles from nitriles, we used nano‐Ag‐TiO₂ as an efficient heterogeneous catalyst for the reaction of various nitriles and sodium azide to afford 5‐substituted tetrazoles in excellent yields. By this method, a wide variety of aryl nitriles underwent [3 + 2] cycloaddition to afford tetrazoles in excellent yields. Further reaction of tetrazoles with ethylchloroacetate resulted in the formation of expected products, except for a bis‐tetrazole, which underwent ring opening and subsequent reaction to afford an unusual product. The bis‐tetrazole also formed an unusual polymeric sodium complex in aq. NaOH solution. X‐ray crystallography revealed a distorted octahedral geometry for the complex, which forms a three‐dimensional network of chains interlinked by bis‐tetrazole moieties through a network of H‐bonds.     

Anchoring Ni (II) on Fe3O4@tryptophan: A recyclable,green and extremely efficient magnetic nanocatalyst for one‐pot synthesis of 5‐substituted 1H‐tetrazoles and chemoselective oxidation of sulfides and thiols

A green, novel and extremely efficient nanocatalyst was successfully synthesized by the immobilization of Ni as a transition metal on Fe₃O₄ nanoparticles coated with tryptophan. This nanostructured material was characterized using Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, thermogravimetric analysis, inductively coupled plasma optical emission spectroscopy, vibrating sample magnetometry and X‐ray diffraction. The prepared nanocatalyst was applied for the oxidation of sulfides, oxidative coupling of thiols and synthesis of 5‐substituted 1H‐tetrazoles. The use of non‐toxic, green and inexpensive materials, easy separation of magnetic nanoparticles from a reaction mixture using a magnetic field, efficient and one‐pot synthesis, and high yields of products are the most important advantages of this nanocatalyst.     

Simple and efficient synthesis of 5‐substituted 1‐H‐tetrazoles using metal‐modified clay catalysts

The synthesis of 5‐substituted 1‐H‐tetrazoles based on reaction of a series of aromatic nitriles with sodium azide was investigated. The reaction was catalyzed by modified montmorillonite K‐10 including Cu²⁺, Fe³⁺, Ni²⁺, and Zn²⁺ metal ions. The best results obtained by Mont‐K10‐Cu catalyst. The catalysts were reused several times without loss of their activity. The present procedure offers advantages such as a shorter reaction time, simple workup, recovery, and reusability of the catalyst. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:168–173, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20672     

Supramolecular Fe3O4@PEG/−diaza crown ether@Ni: a novel magnetically reusable nano catalyst for the clean synthesis of 2‐aryl‐2,3‐dihydroquinazolin‐4(1H)‐ones

Ni@diaza crown ether complex supported on magnetic nanoparticle was provided by grafting technique. The catalytic activity of Fe₃O₄@diaza crown ether@Ni was explored through one‐pot synthesis of 2,3‐dihydroquinazolin‐4(1H)‐ones and it was used as an efficient and recoverably constant nanocatalyst. FT‐IR, SEM, TEM, XRD, BET, ICP, EDS, and TGA techniques were employed to specify the nanocatalyst. This heterogeneous catalyst demonstrated acceptable recyclability and could be used again several times with no considerable loss of its catalytic activity.     

Application of Pd‐2A3HP‐MCM‐41 to the Suzuki,Heck and Stille coupling reactions and synthesis of 5‐substituted 1H‐tetrazoles

An ecofriendly heterogeneous catalyst has been synthesized by anchoring palladium onto the surface of organically modified mesoporous silica. The prepared catalyst was characterized using X‐ray diffraction, Fourier transform infrared and energy‐dispersive X‐ray spectroscopies, transmission and scanning electron microscopies, inductively coupled plasma and thermogravimetric techniques. The catalyst shows high activity in the Suzuki, Heck and Stille cross‐coupling reactions and the synthesis of 5‐substituted 1H‐tetrazoles from sodium azide (NaN₃). These methods have the advantages of high yields, green reaction conditions, simple methodology and easy separation and workup. Copyright © 2016 John Wiley & Sons, Ltd.     

Biosynthesis of Pd/MnO2 nanocomposite using Solanum melongena plant extract and its application for the one‐pot synthesis of 5‐substituted 1H‐tetrazoles from aryl halides

In this work, for the first time, Solanum melongena plant extract was used for the green synthesis of Pd/MnO₂ nanocomposite via reduction osf Pd(II) ions to Pd(0) and their immobilization on the surface of manganese dioxide (MnO₂) nanoparticles (NPs) as an effective support. The synthesized nanocomposite were characterized by various analytical techniques such as Fourier transform infrared (FT‐IR), X‐ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X‐ray spectroscopy (EDS) and UV–Vis spectroscopy. The catalytic activity of Pd/MnO₂ nanocomposite was used as a heterogeneous catalyst for the one‐pot synthesis of 5‐substituted 1H‐tetrazoles from aryl halides containing various electron‐donating or electron‐withdrawing groups in the presence of K ₄ [Fe (CN) ₆ ] as non‐toxic cyanide source and sodium azide. The products were obtained in good yields via a simple methodology and easy work‐up. The nanocatalyst can be recycled and reused several times with no remarkable loss of activity.     

Expeditious synthesis of diverse spiro fused quinoxaline derivatives using magnetically separable core–shell CoFe2O4@SiO2‐SO3H nanocatalyst under ultrasonication

A magnetically separable core–shell CoFe₂O₄@SiO₂‐SO₃H nanocatalyst has been successfully exploited as a heterogeneous acid catalyst in the synthesis of diversely substituted biologically important spiro fused pyrrolo/indolo[1,2‐a]quinoxaline derivatives through the condensation of N‐(2‐aminophenyl)pyrroles/indoles and various cyclic conjugated 1,2‐diones in ethanol under ultrasonic irradiation. Room temperature synthesis, short reaction time, wide substrate scope, good to excellent yield of products and use of a magnetically separable and recyclable nanocatalyst make this method attractive and practicable.     

Phosphotungstic acid grafted zeolite imidazolate framework as an effective heterogeneous nanocatalyst for the one‐pot solvent‐free synthesis of 3,4‐dihydropyrimidinones

Phosphotungstic acid (H₃PW₁₂O₄₀, PTA) supported on ZIF‐9(NH₂) was synthesized for the first time and performed as an effective and environmental friendly catalyst in the one‐pot three component Biginelli condensation of different substituted benzaldehydes with ethyl acetoacetate and urea to afford the corresponding 3,4‐dihydropyrimidin‐2‐(1H)‐ones under solvent‐free conditions. ZIF‐9(NH₂) and the prepared nanocatalyst PTA@ZIF‐9(NH₂) were characterized by XRD, FESEM, TEM, EDX, BET, AAS, TGA, UV–Vis, and FT‐IR. After reaction, the nanocatalyst can be easily separated from the reaction mixture by centrifuge and the recovered catalyst can be reused for at least five times with a 14% reduction in yield after the fifth run. This study showed that ZIF‐9(NH₂) can be utilized as a promising support for PTA and developed a highly active, stable and reusable heterogeneous catalyst under easy reaction condition in the multi‐component organic synthesis.     

Engineering a Cu‐MOF Nano‐Catalyst by using Post‐Synthetic Modification for the Preparation of 5‐Substituted 1H‐Tetrazoles

A new nano scale Cu‐MOF has been obtained via post‐synthetic metalation by immersing a Zn‐MOF as a template in DMF solutions of copper(II) salts. The Cu‐MOF serves as recyclable nano‐catalyst for the preparation of 5‐substituted 1H‐tetrazoles via [3 + 2] cycloaddition reaction of various nitriles and sodium azide in a green medium (PEG). The post‐synthetic metalated MOF were characterized by FT‐IR spectroscopy, powder X‐ray diffraction (PXRD), atomic absorption spectroscopy (AAS), and energy dispersive X‐ray spectroscopy (EDX) techniques. The morphology and size of the nano‐catalyst were determined by field emission scanning electron microscopy (FE‐SEM).