Tungstate supported mesoporous silica SBA‐15 with imidazolium framework as a hybrid nanocatalyst for selective oxidation of sulfides in the presence of hydrogen peroxide

In this work, a new heterogeneous catalyst (SBA‐15/Im/WO₄^2?) was prepared, and then its performance in the oxidation of organic sulfides was studied (using 30% H₂O₂ as green oxidant under neutral reaction conditions). This organic–inorganic hybrid mesoporous material was characterized by various techniques, such as FT‐IR, inductively coupled plasma, X‐ray powder diffraction, high‐resolution‐transmission electron microscopy, N₂ adsorption–desorption and thermogravimetric analysis. The catalyst was also applied to the selective oxidation of various sulfides. The hybrid catalyst was easily recovered, and was very stable and retained good activity for at least five successive runs without any additional activation. Moreover, there was no remarkable decrease in the activity and selectivity of the catalyst. The products could be easily isolated by just removing the solvent after filtering the catalyst. The yields of the catalytic productions through this catalyst were in the range from 75% to 97%.     

Oxidation reactions catalysed by molybdenum(VI) complexes grafted on UiO‐66 metal–organic framework as an elegant nanoreactor

A heterogeneous catalyst was synthesized by immobilizing Mo(CO)₃ in a UiO‐66 metal–organic framework. The benzene ring of the organic linker in UiO‐66 was modified via liquid‐phase deposition of molybdenum hexacarbonyl, Mo(CO)₆, as starting precursor to form the (arene)Mo(CO)₃ species inside the framework. The structure of this catalyst was characterized using X‐ray diffraction, and chemical integrity was confirmed using Fourier transform infrared and diffuse reflectance UV–visible spectroscopic methods. The metal content was analysed with inductively coupled plasma. Field emission scanning electron microscopy was used to measure particle size and N₂ adsorption measurements to characterize the specific surface area. This catalytic system was efficiently applied for epoxidation of alkenes and oxidation of sulfides. The Mo‐containing metal–organic framework was reused several times without any appreciable loss of its efficiency.     

Fe3O4@S‐ABENZ@VO: Magnetically separable nanocatalyst for the efficient,selective and mild oxidation of sulfides and oxidative coupling of thiols

Oxovanadium(IV) immobilized on Fe₃O₄@S‐ABEN is reported as a highly efficient nanocatalyst for the oxidation of sulfides and oxidative coupling of thiols (using H₂O₂ as green oxidant), the products of which are obtained in high to excellent yields. The products can be separated by a simple extraction with organic solvent and the catalyst is highly efficient, especially in terms of selectivity of desired product. The catalytic system can be recycled and reused without significant loss of catalytic activity.     

Efficient and recyclable novel Ni‐based metal–organic framework nanostructure as catalyst for the cascade reaction of alcohol oxidation–Knoevenagel condensation

A novel Ni‐based metal–organic framework (Ni‐MOF) with a Schiff base ligand as an organic linker, Ni₃(bdda)₂(OAc)₂?6H₂O (H₂bdda = 4,4′‐[benzene‐1,4‐diylbis(methylylidenenitrilo)]dibenzoic acid), was synthesized and characterized using powder X‐ray powder diffraction, thermogravimetric analysis, Brunauer–Emmett–Teller measurements, inductively coupled plasma atomic emission spectroscopy, transmission electron microscopy, elemental analysis and Fourier transform infrared spectroscopy. The synthesized Ni‐MOF exhibited a high catalytic activity in benzyl alcohol oxidation using tert‐butyl hydroperoxide under solvent‐free conditions. Also, the efficiency of the catalyst was investigated in the cascade reaction of oxidation–Knoevanagel condensation under mild conditions. The Ni‐MOF catalyst could be recovered and reused four times without significant reduction in its catalytic 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.     

Scaled‐up,selective and green synthesis of sulfoxides under mild conditions using (CeIII‐MoVI)Ox/aniline hybrid rods as an efficient catalyst

A novel hybrid material, (Ce^III‐Mo^VI)O_x/aniline, with rod‐like morphology is synthesized through a wet chemical method using Mo₃O₁₀(C₆H₅NH₃)₂.2H₂O nanowires as precursor. The synthesized materials are characterized by XRD, XPS, SEM, TEM, FTIR, Raman, UV–Vis, TGA, and elemental analysis. Also, their catalytic activities as a hybrid catalyst are tested in the selective oxidation of sulfides using hydrogen peroxide as a green oxidant. The proposed novel hybrid catalyst shows an excellent performance under green conditions at mild temperature. Furthermore, the scalability of the oxidation reaction is shown by making multi‐gram quantities at optimized conditions.     

CoFe2O4@SiO2‐CPTES‐Guanidine‐Cu(II): A novel and reusable nanocatalyst for the synthesis of 2,3‐dihydroquinazolin‐4(1H)‐ones and polyhydroquinolines and oxidation of sulfides

CoFe₂O₄@SiO₂‐CPTES‐Guanidine‐Cu(II) magnetic nanoparticles were synthesized and used as a new, inexpensive and efficient heterogeneous catalyst for the synthesis of polyhydroquinolines and 2,3‐dihydroquinazoline‐4(1H)‐ones and for the oxidation of sulfides. The structure of this nanocatalyst was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, vibrating sample magnetometry, thermogravimetric analysis, X‐ray diffraction and inductively coupled plasma optical emission spectrometry. Simple preparation, high catalytic activity, simple operation, high yields, use of green solvents, easy magnetic separation and reusability of the catalyst are some of the advantages of this protocol.     

Iron oxide on carbon‐based supports as efficient catalysts for organic compounds oxidation

For the first time, iron oxide on carbon aerogel, amine functionalized carbon nanotube, black carbon and carboxylic acid functionalized carbon nanotube in the presence of H₂O₂ was reported as an efficient and stable catalyst for the selective oxidation of sulfides and alcohols. The catalysts were characterized by scanning electron microscopy, energy‐dispersive spectroscopy, transmission electron microscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction, Fourier transform infrared spectroscopy and atomic absorption spectroscopy. In the next step, catalytic reactivity toward sulfide to sulfoxide and alcohol to aldehyde/ketone oxidation in the presence of H₂O₂ was studied and discussed.     

Nanoscaled Copper Metal–Organic Framework (MOF) Based on Carboxylate Ligands as an Efficient Heterogeneous Catalyst for Aerobic Epoxidation of Olefins and Oxidation of Benzylic and Allylic Alcohols

Aerobic epoxidation of olefins at a mild reaction temperature has been carried out by using nanomorphology of [Cu₃(BTC)₂] (BTC=1,3,5‐benzenetricarboxylate) as a high‐performance catalyst through a simple synthetic strategy. An aromatic carboxylate ligand was employed to furnish a heterogeneous copper catalyst and also serves as the ligand for enhanced catalytic activities in the catalytic reaction. The utilization of a copper metal–organic framework catalyst was further extended to the aerobic oxidation of aromatic alcohols. The shape and size selectivity of the catalyst in olefin epoxidation and alcohol oxidation was investigated. Furthermore, the as‐synthesized copper catalyst can be easily recovered and reused several times without leaching of active species or significant loss of activity.     

Molybdenum (VI)‐functionalized UiO‐66 provides an efficient heterogeneous nanocatalyst in oxidation reactions

A novel heterogeneous nanocatalyst was established by supporting molybdenum (VI) on Zr₆ nodes in the structure of the well‐known UiO‐66 metal–organic framework (MOF). The structure of the UiO‐66 before and after Mo (VI) immobilization was confirmed with XRD, DR‐FTIR and UV–vis spectroscopy, and the presence and amount of Mo (VI) was identified by X‐ray photoelectron spectroscopy and inductively coupled plasma atomic emission spectroscopy. TEM imaging confirmed the absence of Mo clusters on the MOF surface, while SEM confirmed that the appearance of the MOF has not changed upon immobilizing the Mo (VI) catalyst. BET adsorption measurements were used to confirm the porosity of the catalyst. The catalytic activity of this heterogeneous catalyst was investigated in oxidation of sulfides with H₂O₂ in acetonitrile and oxidative desulfurization of dibenzothiophene. Easy work up, convenient and steady reuse and high activity and selectivity are prominent properties of this new hybrid material.     

Visible‐Light‐Induced Photoredox Catalysis of Dye‐Sensitized Titanium Dioxide: Selective Aerobic Oxidation of Organic Sulfides

TiO₂ photoredox catalysis has recently attracted much interest for use in performing challenging organic transformations under mild reaction conditions. However, the reaction scheme is hampered by the fact that TiO₂ can only be excited by UV light of wavelengths λ shorter than 385 nm. One promising strategy to overcome this issue is to anchor an organic, preferably metal‐free dye onto the surface of TiO₂. Importantly, we observed that the introduction of a catalytic amount of the redox mediator TEMPO [(2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl] ensured the stability of the anchored dye, alizarin red S, thereby resulting in the selective oxidation of organic sulfides with O₂. This result affirms the essential role of the redox mediator in enabling the organic transformations by visible‐light photoredox catalysis.     

Magnetically water‐dispersible and recoverable rhodium organometallic catalyst derived from Wilkinson's catalyst for promoting organic reactions

A novel magnetic rhodium catalyst was prepared through immobilizing Wilkinson's catalyst on the surface of silica‐coated iron oxide nanoparticles. After (thio)diphenylphosphine (─S&─PPh₂) was modified on the surface of the silica‐coated iron oxide nanoparticles, tris(triphenylphosphine)rhodium(I) chloride was employed to synthesize the Rh(Cl)(PPh₃)₂(Ph₂P&─S&─) complex, affording a rhodium loading of 0.16 mmol g⁻¹. The Rh(I) organometallic magnetic nanoparticles form a novel class of heterogeneous catalyst which is particularly suitable for the practice of organic synthesis. The prepared system exhibits high catalytic efficiency in Suzuki–Miyaura and Miyaura–Michael reactions in ethanol–water solution. High yield, low reaction times, use of green solvents and non‐toxicity of the catalyst are the main merits of this protocol. Also, magnetic separation is an environmentally friendly alternative for the recovery of the catalyst, since it minimizes energy and catalyst loss by preventing mass loss and oxidation. The produced catalyst was characterized using a variety of techniques.     

Green route for selective gram‐scale oxidation of sulfides using tungstate/triazine‐based ionic liquid immobilized on magnetic nanoparticles as a phase‐transfer heterogeneous catalyst

Tungstate ions were successfully loaded onto triazine‐based ionic liquid‐functionalized magnetic nanoparticles through an anion exchange process. The use of triazine core for creating ionic liquid led to the immobilization of high amounts of WO₄^2?. The resulting catalyst showed high activity and selectivity in the oxidation of sulfides to sulfoxides with H₂O₂ as a green oxidant at room temperature. In addition, due to the presence of ammonium groups in the catalyst structure, water dispersibility of the catalyst was increased. More important, the catalyst was magnetically recovered and reused for up to six runs without any marked decrease of activity and selectivity. Finally, easy gram‐scale oxidation of methylphenyl sulfide as well as fast separation of catalyst and product makes the protocol economical and industrially applicable.     

Ni(II)‐Adenine complex coated Fe3O4 nanoparticles as high reusable nanocatalyst for the synthesis of polyhydroquinoline derivatives and oxidation reactions

In the present study, Fe₃O₄ nanoparticles were prepared via simple and versatile procedure. Then, a novel and green catalyst was synthesized by the immobilization of Ni on Fe₃O₄ nanoparticles coated with adenine. The activity of this nanostructure compound was examined for the oxidation of sulfides, oxidative coupling of thiols and synthesis of polyhydroquinolines. The prepared catalyst was characterized by Fourier transform infrared spectroscopy (FT‐IR), scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDS), inductively coupled plasma optical emission spectroscopy (ICP‐OES), X‐ray Diffraction (XRD), thermal gravimetric analysis (TGA), and vibrating sample magnetometer (VSM) measurements. This organometallic catalyst was recovered by the assistance of an external magnetic field from the reaction mixture and reused for seven continuous cycles without noticeable change in its catalytic activity.     

Transition‐Metal‐Free Oxidative Cross‐Coupling of Tetraarylborates to Biaryls Using Organic Oxidants

Readily prepared tetraarylborates undergo selective (cross)‐coupling through oxidation with Bobbitt's salt to give symmetric and unsymmetric biaryls. The organic oxoammonium salt can be used either as a stoichiometric oxidant or as a catalyst in combination with in situ generated NO₂ and molecular oxygen as the terminal oxidant. For selected cases, oxidative coupling is also possible with NO₂/O₂ without any additional nitroxide‐based cocatalyst. Transition‐metal‐free catalytic oxidative ligand cross‐coupling of tetraarylborates is unprecedented and the introduced method provides access to various biaryl and heterobiaryl systems.     

Liquid-phase catalytic oxidation of organic substrates by a recyclable polymer-supported copper(II) complex

Chloromethylated polystyrene beads cross-linked with 6.5 % divinylbenzene were functionalized with 2-(2′-pyridyl) benzimidazole (PBIMH) and on subsequent treatment with Cu(OAc)₂ in methanol gave a polymer-supported diacetatobis(2-pyridylbenzimidazole)copper(II) complex [PS-(PBIM)₂Cu(II)], which was characterized by physicochemical techniques. The supported complex showed excellent catalytic activity toward the oxidation of industrially important organic compounds such as phenol, benzyl alcohol, cyclohexanol, styrene, and ethylbenzene. An effective catalytic protocol was developed by varying reaction parameters such as the catalyst and substrate concentrations, reaction time, temperature, and substrate-to-oxidant ratio to obtain maximum selectivity with high yields of products. Possible reaction mechanisms were worked out. The catalyst could be recycled five times without any metal leaching or much loss in activity. This catalyst is truly heterogeneous and allows for easy work up, as well as recyclability and excellent product yields under mild conditions.     

Pt Nanoparticles Supported on Nitrogen‐Doped‐Carbon‐Decorated CeO2 for Base‐Free Aerobic Oxidation of 5‐Hydroxymethylfurfural

Currently, the base‐free aerobic oxidation of biomass‐derived 5‐hydroxymethylfurfural (HMF) to produce 2,5‐furandicarboxylic acid (FDCA) is attracting intense interest due to its prospects for the green, sustainable, and promising production of biomass‐based aromatic polymers. Herein, we have developed a new Pt catalyst supported on nitrogen‐doped‐carbon‐decorated CeO₂ (NC‐CeO₂) for the aerobic oxidation of HMF in water without the addition of any homogeneous base. It was demonstrated that the small‐sized Pt particles could be well dispersed on the surface of the hybrid NC‐CeO₂ support, and the activity of the supported Pt catalyst depended strongly on the surface structure and properties of the catalysts. The as‐fabricated Pt/NC‐CeO₂ catalyst, with abundant surface defects, enhanced basicity, and favorable electron‐deficient metallic Pt species, enabled an almost 100 % yield of FDCA in water with molecular oxygen (0.4 MPa) at 110 °C for 8 h without the addition of any homogeneous base, which is indicative of exceptional catalytic performance. Furthermore, this Pt/NC‐CeO₂ catalyst also showed good stability and reusability owing to strong metal–support interactions. An understanding of the role of surface structural defects and basicity of the hybrid NC‐CeO₂ support provides a basis for the rational design of high‐performance and stable supported metal catalysts with practical applications in various transformations of biomass‐derived compounds.     

Cu(II)–Schiff base complex‐functionalized magnetic Fe3O4 nanoparticles: a heterogeneous catalyst for various oxidation reactions

Cu(II)–Schiff base complex‐functionalized magnetic Fe₃O₄ nanoparticles were prepared and characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy techniques. This compound acts as a highly active and selective catalyst for the oxidation of sulfides and thiols. These reactions can be carried out in ethanol or solvent‐free conditions in the presence of hydrogen peroxide with complete selectivity and very high conversion under mild reaction conditions. The designed catalytic system prevents effectively the over‐oxidation of sulfides to sulfones. Separation and recycling can also be easily done using a simple magnetic separation process. Copyright © 2015 John Wiley & Sons, Ltd.     

Zirconium oxide complex‐functionalized MCM‐41 nanostructure: an efficient and reusable mesoporous catalyst for oxidation of sulfides and oxidative coupling of thiols using hydrogen peroxide

Zirconium oxide complex‐functionalized mesoporous MCM‐41 (Zr‐oxide@MCM‐41) as an efficient and reusable catalyst is reported for the oxidation of sulfides into sulfoxides using hydrogen peroxide (H₂O₂) as the oxidant, with short reaction times in good to excellent yields at room temperature under solvent‐free conditions. Also, a simple and efficient method is reported for the oxidative coupling of thiols into corresponding disulfides in good to high yields using H₂O₂ as oxidant in the presence of Zr‐oxide@MCM‐41 as recoverable catalyst in ethanol at room temperature. A series of sulfides and thiols possessing functional groups was successfully converted into corresponding products. After completion of reactions the catalyst was easily separated with simple filtration from the reaction mixture and reused for several consecutive runs without significant loss of catalytic efficiency. The mesoporous catalyst was characterized using Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller surface area measurements, X‐ray diffraction, transmission and scanning electron microscopies, energy‐dispersive X‐ray spectroscopy and thermogravimetric analysis. Copyright © 2015 John Wiley & Sons, Ltd.     

CoFe2O4@SiO2@ Co (III) salen complex nanoparticle as a green and efficient magnetic nanocatalyst for the oxidation of benzyl alcohols by molecular O2

In the presence of cobalt (III) salen complex, selective oxidation of alcohols to carbonyl compounds was studied by molecular oxygen using isobutyraldehyde as an oxygen acceptor. The effect of cobalt (III) salen complex in the oxidation reaction was studied, and the results showed that Co (III) salen complex is very active and selective in the oxidation of various alcohols. Also, the effect of important factors including catalyst amount, solvent and temperature was investigated on the reaction. Furthermore, the catalytic activities of CoFe₂O₄@SiO₂‐supported Schiff base metal complex as well as the effect of molecular oxygen (O₂) as a green oxidant were studied. The results showed that benzaldehyde was the major product and the heterogeneous catalyst was highly reusable.