Multilayer‐Functionalized Reduced Graphene Oxide Decorated with Gold Nanoparticles as a Designed Nanonanocatalyst for the Selective Oxidation of Cyclohexene by Molecular Oxygen in a Solvent‐Free System

The aerobic oxidation of cyclohexene is of great significance from the viewpoints of both fundamental and industry studies as it can transfer the petrochemical feedstock into valuable chemicals. In this research, gold nanoparticles were synthesized on the multi‐layer functionalized reduced graphene oxide . The surface of reduced graphene oxide (rGO) was modified with hydrophobic and hydrophilic layers to create the rGO with scattered hydrophilic positions. The gold nanoparticles were synthesized and immobilized simultaneously in small hydrophilic micro reactors in a mild condition. Characterization of synthesized nanocatalyst was confirmed with different techniques such as TEM, XRD, FT‐IR, and SEM. TEM images of synthesized catalyst show the gold nanoparticles have diameters less than 5 nm. Designed nanonanocatalyst was investigated for the selective liquid phase oxidation of cyclohexene with molecular oxygen in solvent free condition which after optimized conditions a maximum of 88% conversion and 91% selectivity was obtained.     

Monodisperse CuPt alloy nanoparticles assembled on reduced graphene oxide as catalysts in the transfer hydrogenation of various functional organic groups

We present herein a new nanocatalyst, namely binary CuPt alloy nanoparticles (NPs) supported on reduced graphene oxide (CuPt‐rGO), as a highly active heterogeneous catalyst for the transfer hydrogenation (TH) protocol that is demonstrated to be applicable over the reduction of various unsaturated organic compounds (olefins, aldehydes/ketones and nitroarenes) in aqueous solutions at room temperature. CuPt alloy NPs were synthesized by the co‐reduction of metal (II) acetylacetonates by borane‐tert‐butylamine (BTB) complex in hot oleylamine (OAm) solution and then assembled on reduced graphene oxide (rGO) via ultrasonic‐assisted liquid phase self‐assembly method. The structure of yielded CuPt NPs and CuPt‐rGO nanocatalyst were characterized by TEM, XRD and ICP‐MS. The activity of Cu₇Pt₃‐rGO nanocatalysts were then tested for the THs that were conducted in a commercially available high‐pressure tube using water as sole solvent and ammonia borane as a hydrogen donor at room temperature. The presented catalytic TH protocol was successfully applied over nitroarenes, olefines and aldehydes/ketones, and all the tested compounds were converted to corresponding reduction products with the yields reaching up to 99% under ambient conditions. Moreover, the Cu₇Pt₃‐rGO nanocatalyst was also reusable in the TH by providing 99% yield after five consecutive runs in TH of nitrobenzene as an example.     

Fe3O4‐Methylene diphenyl diisocyanate‐guanidine (Fe3O4–4,4′‐MDI‐Gn): A novel superparamagnetic powerful basic and recyclable nanocatalyst as an efficient heterogeneous catalyst for the Knoevenagel condensation and tandem Knoevenagel‐Michael‐cyclocondensation reactions

In this paper, guanidine groups (Gn) supported on modified magnetic nanoparticles (Fe₃O₄–4,4′‐MDI) were synthesized for the first time. The catalyst synthesized was characterized by various techniques such as SEM (Scanning Electron Microscopy), TEM (Transmission electron microscopy), XRD ( X‐ray Diffraction ), TGA (Thermogravimetric ananlysis), EDS ( Energy‐dispersive X‐ray spectroscopy ) and VSM (vibrating sample magnetometer). The catalyst activity of modified MNPs–MDI‐Gn, as powerful basic nanocatalyst, was probed through the Knoevenagel and Tandem Knoevenagel–Michael‐cyclocondensation reactions. Conversion was high under optimal conditions, and reaction time was remarkably shortened. This nanocatalyst could simply be separated and recovered from the reaction mixture by simple magnetic decantation and reused many times without significant loss of its catalytic activity. Also, the nanocatalyst could be recycled for at least seven (Knoevenagel condensation) and six (Knoevenagel and Tandem Knoevenagel–Michael‐cyclocondensation) additional cycles after they were separated by magnetic decantation and, washed with ethanol, air‐dried, and immediately reused.     

Liquid phase selective hydrogenation of phenol to cyclohexanone over Ru/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocatalyst under mild conditions

Highly monodispersed ruthenium nanoparticles were prepared via wet impregnation technique using RuCl₃ · nH₂O as a precursor. Ru nanoparticles were supported on Al₂O₃ to synthesize Ru nanocatalyst. The nanocatalyst was characterized by various techniques like XRD, SEM, TEM and BET analysis. The catalyst was used for hydrogenation of phenol under mild condition. The activity of the catalyst was checked by varying different parameters such as reaction temperature, time, H₂ partial pressure, metal loading and catalyst amount. The catalyst was recovered from product and reused up to four times without significant loss in its catalytic activity. After a reaction time of 1 h, Ru/Al₂O₃ nanocatalyst showed high reactivity (82% conversion) and selectivity to cyclohexanone (67%) at 80°C and 20 bar hydrogen pressure.     

Preparation and characterization of ruthenium/carbon aerogel nanocomposites via a supercritical fluid route

Carbon-aerogel-supported ruthenium nanoparticles were synthesized by impregnating carbon aerogels with Ru(acac)3 or Ru(cod)(tmhd)2 from supercritical carbon dioxide (scCO2) solutions, followed by thermal reduction of these precursors. Two different carbon aerogels with pore diameters of 4 and 21 nm were synthesized. The kinetics and the thermodynamics of impregnation of carbon aerogels with the ruthenium coordination complexes were studied. The approach-to-equilibrium data indicated very fast adsorption, and the adsorption isotherms were found to follow the Langmuir model. The impregnated carbon aerogel complexes were reduced thermally at different temperatures between 300 and 1000 degrees C in the presence of nitrogen. The resulting nanocomposites were characterized using transmission electron microscopy (TEM) and hydrogen chemisorption. TEM micrographs showed that the ruthenium nanoparticles were dispersed homogeneously throughout the porous carbon aerogel matrix, and the average sizes obtained under different conditions ranged from 1.7 to 3.8 nm. Once complete decomposition of the precursor had been achieved, the mean size of the ruthenium particles increased with increasing reduction temperature.     

In situ formed catalytically active ruthenium nanocatalyst in room temperature dehydrogenation/dehydrocoupling of ammonia-borane from Ru(cod)(cot) precatalyst

The development of simply prepared and effective catalytic materials for dehydrocoupling/dehydrogenation of ammonia-borane (AB; NH(3)BH(3)) under mild conditions remains a challenge in the field of hydrogen economy and material science. Reported herein is the discovery of in situ generated ruthenium nanocatalyst as a new catalytic system for this important reaction. They are formed in situ during the dehydrogenation of AB in THF at 25 °C in the absence of any stabilizing agent starting with homogeneous Ru(cod)(cot) precatalyst (cod = 1,5-η(2)-cyclooctadiene; cot = 1,3,5-η(3)-cyclooctatriene). The preliminary characterization of the reaction solutions and the products was done by using ICP-OES, ATR-IR, TEM, XPS, ZC-TEM, GC, EA, and (11)B, (15)N, and (1)H NMR, which reveal that ruthenium nanocatalyst is generated in situ during the dehydrogenation of AB from homogeneous Ru(cod)(cot) precatalyst and B-N polymers formed at the initial stage of the catalytic reaction take part in the stabilization of this ruthenium nanocatalyst. Moreover, following the recently updated approach (Bayram, E.; et al. J. Am. Chem. Soc.2011, 133, 18889) by performing Hg(0), CS(2) poisoning experiments, nanofiltration, time-dependent TEM analyses, and kinetic investigation of active catalyst formation to distinguish single metal or in the present case subnanometer Ru(n) cluster-based catalysis from polymetallic Ru(0)(n) nanoparticle catalysis reveals that in situ formed Ru(n) clusters (not Ru(0)(n) nanoparticles) are kinetically dominant catalytically active species in our catalytic system. The resulting ruthenium catalyst provides 120 total turnovers over 5 h with an initial turnover frequency (TOF) value of 35 h(-1) at room temperature with the generation of more than 1.0 equiv H(2) at the complete conversion of AB to polyaminoborane (PAB; [NH(2)BH(2)](n)) and polyborazylene (PB; [NHBH](n)) units.     

Ruthenium Nanoparticles on Nano‐Level‐Controlled Carbon Supports as Highly Effective Catalysts for Arene Hydrogenation

The reaction of three types of carbon nanofibers (CNFs; platelet: CNF‐P, tubular: CNF‐T, herringbone: CNF‐H) with [Ru₃(CO)₁₂] in toluene heated at reflux provided the corresponding CNF‐supported ruthenium nanoparticles, Ru/CNFs (Ru content=1.1–3.8 wt %). TEM studies of these Ru/CNFs revealed that size‐controlled Ru nanoparticles (2–4 nm) exist on the CNFs, and that their location was dependent on the surface nanostructures of the CNFs: on the edge of the graphite layers (CNF‐P), in the tubes and on the surface (CNF‐T), and between the layers and on the edge (CNF‐H). Among these Ru/CNFs, Ru/CNF‐P showed excellent catalytic activity towards hydrogenation of toluene with high reproducibility; the reaction proceeded without leaching of the Ru species, and the catalyst was reusable. The total turnover number of the five recycling experiments for toluene hydrogenation reached over 180 000 (mol toluene) (mol Ru)^?1. Ru/CNF‐P was also effective for the hydrogenation of functionalized benzene derivatives and pyridine. Hydrogenolysis of benzylic C? O and C? N bonds has not yet been observed. Use of poly(ethylene glycol)s (PEGs) as a solvent made possible the biphasic catalytic hydrogenation of toluene. After the reaction, the methylcyclohexane formed was separated by decantation without contamination of the ruthenium species and PEG. The insoluble PEG phase containing all of the Ru/CNF was recoverable and reusable as the catalyst without loss of activity.     

N-Heterocyclic Carbene (NHC)-Stabilized Ru0 Nanoparticles: In Situ Generation of an Efficient Transfer Hydrogenation Catalyst

Tethered and untethered ruthenium half-sandwich complexes were synthesized and characterized spectroscopically. X-ray crystallographic analysis of three untethered and two tethered Ru N-heterocyclic carbene (NHC) complexes were also carried out. These RuNHC complexes catalyze transfer hydrogenation of aromatic ketones in 2-propanol under reflux, optimally in the presence of (25 mol %) KOH. Under these conditions, the formation of 2–3 nm-sized Ru⁰ nanoparticles was detected by TEM measurements. A solid-state NMR investigation of the nanoparticles suggested that the NHC ligands were bound to the surface of the Ru nanoparticles (NPs). This base-promoted route to NHC-stabilized ruthenium nanoparticles directly from arene-tethered ruthenium–NHC complexes and from untethered ruthenium–NHC complexes is more convenient than previously known routes to NHC-stabilized Ru nanocatalysts. Similar catalytically active RuNPs were also generated from the reaction of a mixture of [RuCl₂(p-cymene)]₂ and the NHC precursor with KOH in isopropanol under reflux. The transfer hydrogenation catalyzed by these NHC-stabilized RuNPs possess a high turnover number. The catalytic efficiency was significantly reduced if nanoparticles were exposed to air or allowed to aggregate and precipitate by cooling the reaction mixtures during the reaction.     

Solid‐State Electrochemistry and Electrochemiluminescence of Porous Thin Film of [(2,2′‐Bipyridyl)(4‐(2‐pyrrol‐1‐ylethyl)‐4′‐methyl‐2,2′‐bipyridyl)2]ruthenium(II) Monomer Precipitation

A novel fluorescent porous thin film based on the precipitation of the [(2,2′‐bipyridyl)(4‐(2‐pyrrol‐1‐ylethyl)‐4′‐methyl‐2,2′‐bipyridyl)₂]ruthenium(II) (BF₄)₂ complex (pyr‐Ru) was fabricated by easily spreading 2 µL of pyr‐Ru (1 mM in acetonitrile solution) onto the surface of a platinum electrode and drying it in ambient conditions. The morphology of the resulting pyr‐Ru thin film was characterized by scanning electron microscopy (SEM) and fluorescence microscopy. The coating exhibits fluorescent properties of the ruthenium complex and a porous structure with pore diameters of micrometers. The solid‐state electrochemistry and electrochemiluminescence behaviors of the porous pyr‐Ru thin film were investigated in aqueous solution by cyclic voltammetry and step potential.     

Synthesis and characterization of 4‐AMTT‐Pd(II) complex over Fe3O4@SiO2 as supported nanocatalyst for Suzuki‐Miyaura and Mizoroki‐heck cross‐coupling reactions in water

Immobilization of Pd(II) nanoparticles on silica‐coated modified magnetite particles has been readily achieved via a surface modification of Fe₃O₄ particles with 4‐amino‐5‐methyl‐4‐H‐1,2,4‐triazole‐3‐thiol (4‐AMTT) as a ligand. This magnetite nanocatalyst was characterized by various analyses such as FT‐IR, SEM/EDX, ICP‐AES, VSM, TEM, XRD, XPS and TGA. This nanocatalyst showed admirable catalytic activity for Suzuki‐Miyaura and Mizoroki‐Heck cross‐coupling reactions under mild conditions in water, and could be simply separated by an outer magnet and reused for several times.     

One‐pot multicomponent synthesis of novel 2‐(piperazin‐1‐yl) quinoxaline and benzimidazole derivatives,using a novel sulfamic acid functionalized Fe3O4 MNPs as highly effective nanocatalyst

The immobilization of sulfonic acid on the surface of Fe₃O₄ magnetic nanoparticles (MNPs) as a novel acid nanocatalyst has been successfully reported. The morphological features, thermal stability, magnetic properties, and other physicochemical properties of the prepared superparamagnetic core–shell (Fe₃O₄@PFBA–Metformin@SO₃H) were thoroughly characterized using Fourier transform infrared (FTIR), X‐ray diffraction (XRD), energy‐dispersive X‐ray spectroscopy (EDS), field‐emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), thermogravimetric analysis–differential thermal analysis (TGA‐DTA), atomic force microscopy (AFM), dynamic light scattering (DLS), Brunauer–Emmett–Teller (BET), and vibrating sample magnetometer (VSM) techniques. It was applied as an efficient and reusable catalyst for the synthesis of 2‐(piperazin‐1‐yl) quinoxaline and benzimidazole derivatives via a one‐pot multiple‐component cascade reaction under green conditions. The results displayed the excellent catalytic activity of Fe₃O₄@PFBA–metformin@SO₃H as an organic–inorganic hybrid nanocatalyst in condensation and multicomponent Mannich‐type reactions. The easy separation, simple workup, excellent stability, and reusability of the nanocatalyst and quantitative yields of products and short reaction time are some outstanding advantages of this protocol.     

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.     

Small Pd nanoparticles supported in large pores of mesocellular foam: an excellent catalyst for racemization of amines

Highly dispersed palladium nanoparticles (1–2 nm) supported in large‐pore mesocellular foam (MCF; 29 nm) were synthesized. The Pd‐nanocatalyst/MCF system was characterized by transmission electron microscopy (TEM), powder X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS). The performance of the Pd nanocatalyst obtained was examined for amine racemization. The Pd nanocatalyst showed higher activity and selectivity toward racemization of (S)‐1‐phenylethyl amine than any other amine racemization catalyst reported so far and it could be reused several times. Our data from TEM and XRD suggest a restructuring of the Pd nanocatalyst from amorphous to crystalline and an increase in Pd nanocatalyst size during the racemization reaction. This led to an unexpected increase of activity after the first use. The Pd nanocatalyst obtained can be integrated with other resolving processes of racemic organic compounds to increase the yield of chiral organic products.     

Enhanced visible‐light‐driven photocatalytic activity of F doped reduced graphene oxide ‐ Bi2WO6 photocatalyst

The reduced graphene oxide‐Bi₂WO₆ (rGO‐BWO) photocatalysts with the different R_F/O values (molar ratio of the F molar mass and the O's molar mass of Bi₂WO₆) had been successfully synthesized via one‐step hydrothermal method. The F‐doped rGO‐BWO samples were characterized by X‐ray diffraction patterns (XRD), field‐emission scanning electron microscopy (FE‐ESEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller surface area (BET), X‐ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectra (DRS). The results indicate that F^? ions had been successfully doped into rGO‐BWO samples. With the increasing of the R_F/O values from 0 to 2%, the evident change of the morphology and the absorption edges of F‐doped rGO‐BWO samples and the photocatalytic activities had been enhanced. Moreover, the photocatalytic activity of F‐doped rGO‐BWO with R_F/O = 0.05 were better than rGO‐BWO and the other F‐doped rGO‐BWO under 500 W Xe lamp light irradiation. The enhanced photocatalytic activity can be attributed to the morphology of the intact microsphere that signify the bigger specific surface area for providing more possible reaction sites for the adsorption–desorption equilibrium of photocatalytic reaction, the introduction of F^? ions that may cause the enhancement of surface acidity and creation of oxygen vacancies under visible light irradiation, the narrower band gap which means needing less energy for the electron hole pair transition.     

Amphiphilic dendritic copolymers of tert‐butyl‐glycidylether and glycidol as a nanocontainer for an anticancer ruthenium complex

Dendritic copolymers comprising a hydrophobic core and hydrophilic shell with nearly equal numbers of hydroxyl groups in the shell and different densities in the core were prepared by a multi‐step process based on anionic ring‐opening polymerization. The diversity in the core density was obtained by using copolymer stars with poly(tert‐butyl‐glycidylether)‐block‐polyglycidol arms with nearly equal length of hydrophobic blocks and numbers of hydroxyl groups of polyglycidol but different numbers of arms as macroinitiators. The ability of the dendritic copolymers to serve as a nanocontainer for a ruthenium complex Ru(NH₃)₃Cl₃ with anticancer properties was studied. The possibility of improving the water solubility of this poorly soluble drug by loading it onto dendritic copolymers was investigated. The hydroxyl groups of the dendritic copolymers were used for complexation of the ruthenium compound to the shell. The loading efficiency was analyzed by UV–vis spectroscopy. The dendritic nanoparticles in their hydrated state were visualized using cryo‐TEM. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3488–3497     

N‐(3‐silyl propyl) diethylene triamine N,N',N'‐tri‐sulfonic acid immobilized on Fe3‐xTixO4 magnetic nanoparticles: A new recyclable heterogeneous nanocatalyst for the synthesis of hexahydroquinolines

In the present study, for the first time N‐(3‐silyl propyl) diethylene triamine N,N',N''‐tri‐sulfonic acid (SPDETATSA) was grafted on magnetic Fe_3‐xTi_xO₄ nanoparticles. The structure of the resulted nanoparticles was characterized based on Fourier‐transform infrared (FT‐IR), energy‐dispersive X‐ray spectroscopy (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), and vibrating sample magnetometer (VSM) analyses. The results confirmed the successful immobilization of sulfamic acid groups onto the magnetic support. These nanoparticles exhibited high catalytic activity as novel magnetically recyclable acid nanocatalyst in the synthesis of a diverse range of hexahydroquinolines through one‐pot tandem reactions in excellent yields. Also, this nanocatalyst performed satisfactory catalytic maintenance of activity for the synthesis of the reaction products after 4 rounds of recycling with no considerable loss of activity.     

A Fast‐Initiating Ionically Tagged Ruthenium Complex: A Robust Supported Pre‐catalyst for Batch‐Process and Continuous‐Flow Olefin Metathesis

In this study, a new pyridinium‐tagged Ru complex was designed and anchored onto sulfonated silica, thereby forming a robust and highly active supported olefin‐metathesis pre‐catalyst for applications under batch and continuous‐flow conditions. The involvement of an oxazine–benzylidene ligand allowed the reactivity of the formed Ru pre‐catalyst to be efficiently controlled through both steric and electronic activation. The oxazine scaffold facilitated the introduction of the pyridinium tag, thereby affording the corresponding cationic pre‐catalyst in good yield. Excellent activities in ring‐closing (RCM), cross (CM), and enyne metathesis were observed with only 0.5 mol % loading of the pre‐catalyst. When this powerful pre‐catalyst was immobilized onto a silica‐based cationic‐exchange resin, a versatile catalytically active material for batch reactions was generated that also served as fixed‐bed material for flow reactors. This system could be reused at 1 mol % loading to afford metathesis products in high purity with very low ruthenium contamination under batch conditions (below 5 ppm). Scavenging procedures for both batch and flow processes were conducted, which led to a lowering of the ruthenium content to as little as one tenth of the original values.     

Palladium nanoparticles‐decorated triethanolammonium chloride ionic liquid‐modified TiO2 nanoparticles (TiO2/IL‐Pd): A highly active and recoverable catalyst for Suzuki–Miyaura cross‐coupling reaction in aqueous medium

In this work, an easily obtained procedure was successfully implemented to prepare novel palladium nanoparticles decorated on triethanolammonium chloride ionic liquid‐functionalized TiO₂ nanoparticles [TiO₂/IL‐Pd]. Different methods were carried out for characterizations of the synthesized nanocatalyst (HR‐TEM, XPS, XRD, FE‐SEM, EDX, FT‐IR and ICP). TiO₂/IL‐Pd indicated good catalytic activity for the Suzuki–Miyaura cross‐coupling reaction of arylboronic acid with different aryl halides in aqueous media at ambient temperature. The recycled catalyst was investigated with ICP to amount of Pd leaching after 6 times that had diminished slightly, Thus, was confirmed that the nanocatalyst has a good sustainability for C–C Suzuki–Miyaura coupling reaction. The catalyst can be conveniently separated by filtration of the reaction mixture and reused for 6 times without significant loss of its activity. It supplies an environmentally benign alternative path to the existing protocols for the Suzuki–Miyaura reaction.     

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.     

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.