Immobilized VOsalpr on modified Fe3O4 nanoparticles as a magnetically separable epoxidation catalyst

Fe₃O₄ nanoparticles were prepared and modified with chloropropyl trimethoxysilane (Cl-PTMS). The N,N′-bis(3-salicylidenaminopropyl)amine (salpr) Schiff base ligand was then immobilized on modified Fe₃O₄, which was followed by the addition of VOSO₄ in order to complex it with immobilized sa0lpr. The obtained nanocatalyst designated as VO(Salpr)/SCMNPs was characterized by FT–IR, XRD, SEM, TEM, and VSM techniques. It was found that VO(salpr)/SCMNPs successfully catalyze the epoxidation of allyl alcohols, such as limonene, 1-octene-3-ol, trans-2-hexene-1-ol and geraniol with 50 to 100% conversion and 62 to 100% selectivity with tert-butylhydroperoxide (TBHP). The study of this catalyst's stability and reusability revealed that VO(salpr)/SCMNPs behaves heterogeneously with no desorption during the course of the epoxidation reactions.     

Efficient and selective oxidation of hydrocarbons with tert-butyl hydroperoxide catalyzed by oxidovanadium(IV) unsymmetrical Schiff base complex supported on γ-Fe2O3 magnetic nanoparticles

The catalytic activity of an oxidovanadium(IV) unsymmetrical Schiff base complex supported on γ-Fe₂O₃ magnetic nanoparticles, γ-Fe₂O₃@[VO(salenac-OH)] in which salenac-OH?=?[9-(2′,4′-dihydroxyphenyl)-5,8-diaza-4-methylnona-2,4,8-trienato](-2), was explored in the oxidation of hydrocarbons with tert-butyl hydroperoxide (TBHP, 70% aqueous solution) as oxidant. High catalytic activity and selectivity were demonstrated by this magnetic nanocatalyst in alkane hydroxylation and alkene epoxidation, and the corresponding products were obtained with good to excellent yields in acetonitrile at 50 °C. Reasonable catalytic activity was presented by this supported catalyst in the epoxidation of linear alkenes under optimal reaction conditions. In addition, alkylbenzene derivatives and cycloalkanes can be oxidized to their corresponding alcohols and ketones with good yields in this catalytic system. It is possible to magnetically separate the γ-Fe₂O₃@[VO(salenac-OH)] catalyst and reuse it four times without losing the activity significantly. Moreover, the catalyst structure and morphology do not change after recovery, as indicated by comparing scanning electron microscopy (SEM) image, Fourier transform infrared (FT-IR) and diffuse reflectance spectrum (DRS) of the recovered catalyst with those of the fresh catalyst.

     

One-pot synthesis of VO x /Al 2 O 3 as efficient catalysts for propane dehydrogenation

Vanadium oxides, as highly efficiently catalysts, are widely applied in various catalytic reactions, such as the dehydrogenation of light alkanes and epoxidation of alkenes. In this paper, a series of VO _x /Al ₂ O ₃ catalysts were fabricated by the 1-pot method for catalytic propane dehydrogenation. The results indicated that the VO _x /Al ₂ O ₃ catalysts with loading of 10 wt.% vanadium exhibited optimized catalytic performance. The as-prepared catalysts were characterized by N ₂ adsorption-desorption, XRD, TEM, H ₂ -TPR, and XPS to explore the texture properties, morphology, and electronic environment of vanadium. In addition, several vanadium catalysts were also prepared by the incipient wetness impregnation (IWI) method to compare their catalytic performance with the 1-pot synthesized catalysts. The catalysts synthesized by the 1-pot method exhibited higher selectivity of propylene and longer catalyst lifetime at high propane conversion when compared to the counterpart synthesized by the IWI method.     

Chiral model complexes for methane monooxygenase and their asymmetric catalysis of styrene epoxidation

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Highly efficient epoxidation of alkenes with hydrogen peroxide catalyzed by tungsten hexacarbonyl supported on multi-wall carbon nanotubes

The preparation, characterization, and catalytic activity of W(CO)₆ supported on multi-wall carbon nanotubes modified with 4-aminopyridine is reported. The catalyst, [W(CO)₅@Apy-MWCNT], was characterized by physico-chemical and spectroscopic methods and found to be an efficient heterogeneous catalyst for green epoxidation of alkenes with hydrogen peroxide in MeCN solvent. The catalyst showed good stability and reusability properties in the epoxidation reactions.     

Manganese(III) porphyrin supported on multi-wall carbon nanotubes: A highly efficient and reusable biomimetic catalyst for epoxidation of alkenes with sodium periodate

In this paper, the biomimetic epoxidation of alkenes catalyzed by tetrakis(p-aminophenyl)porphyrinatomanganese(III) chloride, [Mn(TNH₂PP)Cl], supported on functionalized multi-wall carbon nanotubes, MWCNT, is reported. The catalyst, [Mn(TNH₂PP)Cl-MWCNT], was used as an efficient and heterogeneous catalyst for epoxidation of alkenes with NaIO₄ at room temperature, in the presence of imidazole as an axial ligand. This new heterogenized catalyst was characterized by elemental analysis, FT IR spectroscopy, diffuse reflectance UV–Vis spectrophotometry, scanning electron microscopy and transmission electron microscopy. The biggest advantage of Mn(TNH₂PP)Cl-MWCNT is its high reusability in the oxidation reactions, in which the catalyst was reused several times without significant loss of its catalytic activity.     

Effect of ligand structure of Schiff base oxovanadium(IV) complexes on their catalytic activity in aerobic oxidation of alcohols

Two kinds of immobilized bidentate Schiff base oxovanadium(IV) complexes are prepared via polymer reactions and coordination reactions with chloromethylated cross-linked polystyrene (CMCPS) microspheres as matrix. Benzaldehyde (BA)-functionalized CPS microspheres, BA-CPS microspheres, were prepared through nucleophilic substitution with CMCPS microsphere as precursor and p-hydroxy benzaldehyde as reagent, and then Schiff base reactions were carried out with 3-aminopyridine (AP) and glycine (GL) as reagents, respectively, obtaining two kinds of bidentate Schiff base ligand-bonded microspheres, BAAP-CPS microspheres and BAGL-CPS microspheres. Finally, through coordination reactions with vanadyl sulfate (VOSO₄) as reagent, the two kinds of immobilized bidentate Schiff base oxovanadium(IV) complex microspheres, CPS-[VO(BAAP)₂] and CPS-[VO(BAGL)₂], were obtained. The two immobilized complexes, VO(BAAP)₂ and VO(BAGL)₂, are N,N- and N,O-type bidentate Schiff base oxovanadium(IV) complexes and their ligands have different chemical structures. The two catalyst microspheres were used in oxidation of cyclohexanol and benzyl alcohol with molecular oxygen as oxidant and their catalytic activities are compared. The experimental results show that both solid catalysts can catalyze the transformation reactions of cyclohexanol and benzyl alcohol to their corresponding carbonyl compounds under mild conditions. However, CPS-[VO(BAAP)₂] microspheres have much higher catalytic activity and better stability than CPS-[VO(BAGL)₂] microspheres. For the immobilized bidentate Schiff base oxovanadium(IV) catalysts, the catalytic property is closely related to the chemical structures of the ligands, and for this, a theoretical explanation is given.     

可调苯氧基修饰的聚(苯乙烯-苯乙烯基膦酸)-磷酸氢锆固载手性MnⅢ(Salen)高效催化烯烃环氧化

使用不同空间位阻的苯氧链接手臂修饰的聚（苯乙烯基-苯乙烯膦酸）-磷酸氢锆轴向固载手性Mn^Ⅲ（Salen）催化剂（Cat₁-Cat₃）,随后在间氯过氧苯甲酸（m-CPBA）为氧化剂的体系中考察了固载催化剂的催化性能. 同时,在相同氧化体系下测试了一系列均相催化剂类似物（Cat₄-Cat₆）. 结果表明,在非均相条件下,可调变苯氧链接手臂的邻位取代基对催化剂活性起着重要作用,环氧化产物的对映选择性随着取代基位阻的增加而增大,但产物转化率有一定程度下降. 此外,非均相催化剂即使在没有轴向助剂的参与下（通常需要添加,为了增大催化活性）仍然表现出非常高的催化活性,尤其对α-甲基苯乙烯反应,其对映选择性从6.8%增加到76.8%,转化率从19.8%上升到90.7%. 制备的非均相催化剂11次的循环使用实验表明,在前5次使用后催化剂活性与对映选择性没有明显变化.     

Magnetic and catalytic properties of the 2D copper(II) functionalized VPO hybrid system [{Cu(bpy)}2(VO)3(PO4)2(HPO4)2]·2H2O

The hybrid 2D compound [{Cu(bpy)}₂(VO)₃(PO₄)₂(HPO₄)₂]·2H₂O (1), has been investigated due to its interesting magnetic and catalytic properties. Compound (1) acts as an efficient catalyst in the epoxidation of cyclohexene and styrene. The chemoselectivity towards the epoxidation of cyclohexene is notoriously higher than the one observed towards styrene. The bulk antiferromagnetic behaviour of [{Cu(bpy)}₂(VO)₃(PO₄)₂(HPO₄)₂]·2H₂O (1) can be well described with a pentanuclear model, using five J values. Both antiferromagnetic and ferromagnetic interactions mediated by phosphate bridges are found to be present in this hybrid copper(II)–vanadium(IV) material.     

Graphene oxide nanosheets supported manganese(III) porphyrin: a highly efficient and reusable biomimetic catalyst for epoxidation of alkenes with sodium periodate

Efficient epoxidation of alkenes catalyzed by tetrakis(p-aminophenyl)porphyrinatomanganese(III) chloride, [Mn(TNH₂PP)Cl], supported on graphene oxide nanosheets, is reported. The catalyst, [Mn(TNH₂PP)Cl]@GO, was prepared by covalent attachment of amino groups of porphyrin to carboxylic acid groups of GO. This new heterogenized catalyst was characterized by ICP, FT-IR and diffuse reflectance UV–vis spectroscopies, scanning electron microscopy and transmission electron microscopy. This catalyst was applied as an efficient and reusable catalyst in the epoxidation of alkenes with NaIO₄ at room temperature, in the presence of imidazole as axial ligand. The most noteworthy advantage of [Mn(TNH₂PP)Cl]@GO is its high reusability in the oxidation reactions, in which the catalyst was reused several times without significant loss of its catalytic activity.     

Synthesis and catalytic activity of binuclear Mn(III,III)–BINOL complexes for epoxidation of olefins

The novel binuclear complexes [Mn₂^{(III, III)}(BINOL)₃L₂]2H₂O, where, L = 2, 2′‐bipyridine (Bpy) or 1,10‐phenanthroline (Phen) and BINOL = 1, 1′‐bi‐2‐naphthol were synthesized and characterized by elemental analyses, magnetic susceptibility and various spectral methods. The catalytic activity of these complexes was studied for the epoxidation reaction of unfunctionalized olefins like styrene, 1‐hexene, 1‐octene and 1‐decene. The products thus obtained were analyzed by GC. The epoxidation reactions were carried out, in the presence of catalyst with different oxidants, to study the effect of the nature of the oxidant on the reactions. The different oxidants used were the peroxide oxygen donor (e.g. TBHP and H₂O₂), mono oxygen donor (e.g. PhIO) and dioxygen donor (e.g. molecular O₂). TBHP was found to be the best oxidant for the epoxidation reaction. To study the effect of the solvent on the epoxidation, the reactions were carried out in different media, such as a polar media (e.g. with CH₃OH as solvent), non‐polar media (e.g. with CH₂Cl₂ and C₆H₆ as solvents) and coordinating solvent (e.g. CH₃CN). The maximum epoxide formation was observed in CH₂Cl₂ medium. The epoxidation reactions with optically active BINOL catalysts under optimum established conditions were carried out to examine the enantioselectivity of the catalysts. The complexes were, however, found not to be enantioselective. Copyright © 2006 John Wiley & Sons, Ltd.     

Six‐coordinated vanadium(IV) complexes with tridentate task‐specific ionic liquid Schiff base ligands: Synthesis,characterization and effect of ionic nature on catalytic activity

By reaction of 5‐(chloromethyl)salicylaldehyde with triphenylphosphine and N‐methylimidazole in two separate reactions, salicylaldehydetriphenylphosphonium chloride (S²) and salicylaldehydemethylimidazolinium chloride (S³) were prepared. Reaction of 2‐(aminomethyl)pyridine with these aldehydes resulted in the task‐specific ionic liquid Schiff base ligands L¹ and L², respectively. Then six‐coordinated vanadium(IV) Schiff base complexes of VO(acac)L^1–4 were synthesized by reactions of these tridentate Schiff base ligands and VO(acac)₂ in 1:1 stoichiometry. The aldehydes, ligands and VO(acac)L^1–4 complexes were characterized using infrared, ¹H NMR, ¹³C NMR, ³¹P NMR, UV–visible and mass spectroscopies, as well as elemental analysis. Paramagnetic property of the complexes was also studied using magnetic susceptibility measurements. The complexes were used as catalysts in epoxidation of cyclooctene and oxidation of methylphenyl sulfide and the reaction parameters were optimized. The effect of the ionic nature of the complexes was investigated in these oxidation reactions. The catalytic activity of the complexes could be varied by changing the ionic (cationic or anionic) character of VO(acac)L^1–4 catalysts in which counter anion variation showed a greater effect than cationic moiety variation.     

Silica supported Ru(salophen)Cl: An efficient and robust heterogeneous catalyst for epoxidation of alkenes with sodium periodate

In the present work, heterogenization of Ru(salophen)Cl via its axial ligation to silica-bound imidazole, SiIm, is reported. The heterogeneous catalyst, [Ru(salophen)Cl–SiIm], was characterized by elemental analysis, SEM, TEM, FT-IR and diffuse reflectance UV–Vis spectroscopic techniques. The catalyst, which is not soluble in water and common organic solvents, was used for efficient epoxidation of cyclic and linear alkenes with NaIO₄ under agitation with magnetic stirring. This new heterogenized catalyst is of high stability and reusability in the oxidation reactions. The effect of reaction parameters such as solvent and oxidant in the epoxidation of cis-cyclooctene were also investigated.     

An Overview of Heterogeneous Transition Metal-Based Catalysts for Cyclohexene Epoxidation Reaction

Cyclohexane epoxide, which contains highly active epoxy groups, plays a crucial role as an intermediate in the preparation of fine chemicals. However, controlling the epoxidation pathway of cyclohexene is challenging due to issues such as the allylic oxidation of cyclohexene and the ring opening of cyclohexane epoxide during the cyclohexene epoxidation process to form cyclohexane oxide. This review focuses on the structure-activity relationships and synthesis processes of various heterogeneous transition metal-based catalysts used in cyclohexene epoxidation reactions, including molybdenum(Mo)-based, tungsten(W)-based, vanadium(V)-based, titanium(Ti)-based, cobalt(Co)-based, and other catalysts. Initially, the mechanism of cyclohexene epoxidation by transition metal-based catalysts is examined from the perspective of catalytic active centers. Subsequently, the current research of cyclohexene epoxidation catalysts is summarized based on the perspective of catalyst support. Additionally, the differences between alkyl hydroperoxide, hydrogen peroxide (H₂O₂), and oxygen (O₂) as oxidants are analyzed. Finally, the main factors influencing catalytic performance are summarized, and reasonable suggestions for catalyst design are proposed. This work provides scientific support for the advancement of the olefin epoxidation industry.     

Multi-wall carbon nanotube supported tungsten hexacarbonyl: an efficient and reusable catalyst for epoxidation of alkenes with hydrogen peroxide

Highly efficient epoxidation of alkenes with H₂O₂ catalyzed by tungsten hexacarbonyl supported on multi-wall carbon nanotubes (MWCNTs) modified with 1,2-diaminobenzene is reported. The prepared catalyst, [W(CO)₆@DAB-MWCNT], was characterized by elemental analysis, scanning electron microscopy, FT-IR, and diffuse reflectance UV-Vis spectroscopic methods. The prepared catalyst was applied as an efficient catalyst for green epoxidation of alkenes with hydrogen peroxide in CH₃CN. This heterogeneous metal carbonyl catalyst showed high stability and reusability in epoxidation without loss of its catalytic activity.     

Catalytic Performance of Amorphous Ti/SiO2 in the Gas-Phase Epoxidation of Propylene with H2O2

The epoxidation of propylene with dilute H₂O₂ aqueous solution over titanium silicalite-1 (TS-1) zeolite catalyst is a green chemical reaction for propylene oxide (PO) production. Carrying out the reaction in gas-phase can get rid of problems caused by using methanol solvent. This paper reports an attempt of using non-zeolite catalyst for the gas-phase epoxidation. Amorphous Ti/SiO₂, obtained by grafting amorphous SiO₂ with TCl₄ in ethanol solvent in a chemical liquid-phase deposition (CLD) process, has been used as the catalyst. Results show that the CLD Ti/SiO₂ with appropriate Si/Ti molar ratio is an active catalyst for gas-phase epoxidation, achieving 9.8 % propylene conversion and 66.9 % PO selectivity with 40.3 % H₂O₂ utilization, which indicates that this amorphous Ti/SiO₂ catalyst deserves extensive studies in the future.     

Epoxidation of alkenes with NaIO<Subscript>4</Subscript> catalyzed by an efficient and reusable natural polymer-supported ruthenium(III) salophen catalyst

In the present study, preparation, characterization, and catalytic activity of Ru(salophen)Cl supported on chitosan were investigated. The prepared heterogeneous catalyst was characterized by diffuse reflectance UV–vis and FT-IR spectroscopic techniques, scanning electron microscopy, and neutron activation analysis. In this catalytic system, the effects of different solvents were studied in the epoxidation of cis-cyclooctene and CH₃CN/H₂O was found to be a better solvent. Also, the effects of oxygen donors such as NaIO₄, H₂O₂, H₂O₂/urea(UHP), tert-BuOOH, NaClO, and Bu₄NIO₄ were studied in the epoxidation of cis-cyclooctene and NaIO₄ was selected as an oxidant. The catalytic activity of this new heterogeneous catalyst in the epoxidation of cyclic and linear alkenes using NaIO₄ as an oxidant in CH₃CN/H₂O at room temperature was studied. The obtained results led us to conclude that [Ru(salophen)Cl@ chitosan] is an efficient catalyst for the epoxidation of alkenes with NaIO₄. The catalyst can be readily recovered simply by filtration and reused several times without any significant loss in its catalytic activity.     

Stereoselective expoxidation of allylic and homoallylic alcohols with 30% hydrogen peroxide catalyzed by tungstic acid in buffered media

The aqueous tungstic acid-catalyzed hydrogen peroxide epoxidation of allylic alcohols affords the same major diastereoisomer as the VO(acac)₂/tBuOOH system with quite comparable stereoselectivities. In contrast, epoxidation of homoallylic alcohols appears to be much less stereoselective.     

Efficient epoxidation of terminal and internal alkenes using t-butylhydroperoxide catalysed by polybenzimidazole-supported Mo(VI).(PBI.Mo)

A polybenzimidazole-supported Mo complex (PBI.Mo) has been prepared by a method already reported. Extensive investigation of digestion procedures has shown a dry-ashing method using NaNO₃/HNO₃ (conc.) at 560°C to be an optimal method for preparing samples for Mo analysis by atomic absorption spectrophotometric methodology. Mo loadings in the range 1.32–0.62 mmol Mo g⁻¹ polymer were demonstrated. PBI.Mo has been used as a heterogeneous catalyst in the epoxidation of cyclohexene, methylene-cyclohexane, 4-vinyl cyclohexene, styrene, 1,3-pentadiene and allyl chloride, bromide and alcohol using t-butylhydroperoxide as the oxidant. The catalyst is very effective for the first four substrates, somewhat less active than soluble MoO₂acac₂, but providing final yields and purity of products generally better than using MoO₂acac₂. The 1,3-pentadiene displays an overall conversion of ∼35% with a distribution of the four possible monoepoxide isomers similar to that obtained with MoO₂acac₂ as catalyst. The allylic substrates showed poor conversion probably as a result of secondary (oligomerisation) reactions involving the epoxide products. Running the epoxidations for extended periods in air allows in situ generation of alkyl hydroperoxides in the case of cyclohexene and 4-vinylcyclohexene and these are then effective internal oxidants for further Mo catalysed epoxidation of these alkenes. When run under anaerobic conditions the reactions are very clean with no evidence of any free radical processes contributing. In all cases Mo leaching is minimal. Good activity is seen in the recycling of PBI.Mo in the case of styrene and 1,3-pentadiene, although with cyclohexene and 4-vinylcyclohexene steady deactivation is seen, probably as a result of catalyst fouling. Thermogravimetric analyses suggest that it might be possible to burn off the foulant without destroying the catalyst.     

Oxidation of alkenes catalysed by molybdenum(VI)–oxodiperoxo complex anchored on the surface of magnetic nanoparticles under solvent‐free conditions

A new epoxidation catalyst has been prepared by grafting a molybdenum(VI)–oxodiperoxo complex containing an oxazine ligand, [MoO(O₂)₂(phox)], on chloro‐functionalized Fe₃O₄ nanoparticles. The synthesized heterogeneous catalyst (MoO(O₂)₂(phox)/Fe₃O₄ was characterized using powder X‐ray diffraction, scanning and transmission electron microscopies, vibrating sample magnetometry, energy‐dispersive X‐ray analysis, Fourier transform infrared spectroscopy and inductively coupled plasma atomic emission spectroscopy. The immobilized complex gave high product yields and high selectivity for epoxide compared to the corresponding homogeneous one in the epoxidation of various olefins in the presence of tert ‐butyl hydroperoxide at 95°C without any co‐solvent. Also, the heterogeneous catalyst can be recycled without a noticeable change in activity and selectivity.