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.     

Synthesis,characterization and catalytic application of a new organometallic oligomer based on polyhedral oligomeric silsesquioxane

Although homogeneous catalysts provide high performance and selectivity, the difficulty of separation and recycling of these catalysts has bothered the scientific community worldwide. Therefore, the demand for heterogeneous catalysts that possess the advantages of homogeneous ones, with ease of separation and recyclability remains a topic of major impact. The oligomeric catalyst synthesized in this work was characterized using elemental analysis, Fourier transform infrared, ¹³C NMR, ²⁹Si NMR and energy‐dispersive X‐ray spectroscopies, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy and Brunauer–Emmett–Teller analysis and compared to its homogeneous counterpart [W(CO)₃Br₂(ATC)] in the epoxidation of 1‐octene, cyclooctene, (S )‐limonene, cis ‐3‐hexen‐1‐ol, trans ‐3‐hexen‐1‐ol and styrene. The results showed that the percentage conversion for the homogeneous species [W(CO)₃Br₂(ATC)] was slightly higher than for the oligomeric catalyst (POSS‐ATC‐[W(CO)₃Br₂]). Furthermore, the selectivity for epoxide of the oligomeric catalyst was greater than that of the homogeneous catalyst by about 25% when (S )‐limonene was used. Great conversions (yields) of products were obtained with a wide range of substrates and the catalyst was recycled many times without any substantial loss of its catalytic activity.     

Molybdenum hexacarbonyl supported on amine modified multi‐wall carbon nanotubes: an efficient and highly reusable catalyst for epoxidation of alkenes with tert‐butylhydroperoxide

In the present work, highly efficient epoxidation of alkenes catalyzed by Mo(CO)₆ supported on multi‐wall carbon nanotubes modified by 2‐aminopyrazine, APyz‐MWCNTs, is reported. The prepared catalyst was characterized by elemental analysis, scanning electron microscopy, FT IR and diffuses reflectance UV–vis spectroscopic methods. This new heterogenized catalysts, [Mo(CO)₆@APyz‐MWCNT], was used as a highly efficient catalyst for epoxidation of alkenes with tert‐BuOOH. This robust catalyst was reused several times without loss of its catalytic activity. Copyright © 2010 John Wiley & Sons, Ltd.     

Kinetics of 2-methyl-2-pentene epoxidation with tert-butyl hydroperoxide

The reaction rate at the initial period during the epoxidation of 2-methyl-2-pentene with tert-butyl hydroperoxide in the presence of Mo(CO)₆ as catalyst varies linearly in the range of lower concentrations of olefin, hydroperoxide and catalyst. The reaction is losing the first order character in the region of higher concentrations due to the inhibition with the reaction products. This finds the confirmations in a discrepancy between the concentration and the instantaneous (temporal) reaction order.     

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.     

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.     

Laser-initiated catalytic polymerization of vinyl monomer by metal carbonyls

Under the activation of pulsed UV laser, a highly efficient catalyst was formed from W(CO)₆-CCl₄. The polystyrene obtained was characterized by IR spectroscopy and its molecular weight was measured to be 2.5 × 10⁴. The influences of irradiation time, polymerization time and catalyst lifetime were studied. Comparisons of catalysts from W(CO)₆-CCl₄, Mo(CO)₆-CCl₄ and Cr(CO)₆-CCl₄ are made. The comparison between catalytic polymerizations of phenylacetylene and of styrene is also discussed.     

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.     

Asymmetric Allylation of Ketones and Subsequent Tandem Reactions Catalyzed by a Novel Polymer‐Supported Titanium–BINOLate Complex

By using a novel, simple, and convenient synthetic route, enantiopure 6‐ethynyl‐BINOL (BINOL=1,1‐binaphthol) was synthesized and anchored to an azidomethylpolystyrene resin through a copper‐catalyzed alkyne–azide cycloaddition (CuAAC) reaction. The polystyrene (PS)‐supported BINOL ligand was converted into its diisopropoxytitanium derivative in situ and used as a heterogeneous catalyst in the asymmetric allylation of ketones. The catalyst showed good activity and excellent enantioselectivity, typically matching the results obtained in the corresponding homogeneous reaction. The allylation reaction mixture could be submitted to epoxidation by simple treatment with tert‐butyl hydroperoxide (TBHP), and the tandem asymmetric allylation epoxidation process led to a highly enantioenriched epoxy alcohol with two adjacent quaternary centers as a single diastereomer. A tandem asymmetric allylation/Pauson–Khand reaction was also performed, involving simple treatment of the allylation reaction mixture with Co₂(CO)₈/N‐methyl morpholine N‐oxide. This cascade process resulted in the formation of two diastereomeric tricyclic enones in high yields and enantioselectivities.     

UV LASER INITIATED STEREOSELECTIVE HOMOGENEOUS CATALYSIS POLYMERIZATION OF PHENYLACETYLENE

In this paper, the stereoselective homogeneous catalysis polymerization of phenylacetylene by using two kinds of catalysts W(CO)_5CH_3I and W(CO)_4I_2 produced from UV laser photolysis of W (CO)_6 in CH_3I, I_2—C_6H_6 and CHI_3—C_6H_6 respectively was studied. The effects of laser energy, laser irradiation time and lifetime of catalyst on the polymerization of phenylacetylene were discussed. The photoproducts of W (CO)_6 in CH_3I, I2—C_6H_6 and CHI_3—C_6I_6 were determined by IR spectra. The structures of polyphenylacetylene obtained by W (CO)_5CH_3I and W (CO)_4I_2 catalysts were characterized by IR spectra and ~1H NMR spectra.     

A chiral menthyl cyclopentadienyl molybdenum tricarbonyl chloro complex: Synthesis, heterogenization on MCM-41/MCM-48 and application in olefin epoxidation catalysis

The complex [(−)-menthylCp]Mo(CO)₃Cl (1) was synthesized by the reaction of Mo(CO)₃(EtCN)₃ with [(−)-menthylCpH] to produce the hydride [(−)-menthylCp]Mo(CO)₃H. The latter compound was then reacted with CCl₄ to form [(−)-menthylCp]Mo(CO)₃Cl (1). Compound 1 was tested as catalyst for the epoxidation of cis-cyclooctene, styrene and trans-β-methylstyrene in the presence of tert-butyl hydroperoxide (TBHP) at 55 °C using chloroform as solvent. Results under homogeneous conditions prompted the authors to immobilize complex 1 on mesoporous MCM-41 and MCM-48 surfaces leading to the grafted materials AM-41CpMoChi and AM-48CpMoChi. The presence of the organometallic complexes in the materials was confirmed by powder X-ray diffraction, N₂ adsorption/desorption isotherms, TEM, EA, FT-IR, ¹H MAS NMR and TG-MS. AM-41CpMoChi and AM-48CpMoChi were also tested as epoxidation catalysts. The catalytic examinations also included leaching experiments, and the reusing of the grafted materials for several runs.     

Molybdenum Schiff base-polyoxometalate hybrid compound: A heterogeneous catalyst for alkene epoxidation with tert-BuOOH

The hybrid compound consisting of molybdenum(salen) [salen = N,N′-bis(salicylidene)ethylnediamine] complex covalently linked to a lacunary Keggin-type polyoxometalate, K₈[SiW₁₁O₃₉] (POM), was synthesized and characterized by elemental analysis, FT-IR, ¹H NMR and diffuse reflectance UV–Vis spectroscopic methods and BET analysis. The complex, [Mo(O)₂(salen)–POM], was studied, for the first time, in the epoxidation of various alkenes with tert-BuOOH and in 1,2-dichloroethane as solvent. This catalyst can catalyze epoxidation of various olefins including non-activated terminal olefins. The effect of the other parameters such as solvent, oxidant and temperature on the epoxidation of cyclooctene was also investigated. The interesting characteristic of this catalyst is that, in addition to being a heterogeneous catalyst, it gives higher yields towards epoxidation of olefins in comparison to the corresponding homogeneous [Mo(O)₂(salen)] complex.     

Castor oil modified by epoxidation,transesterification, and acrylation processes: Spectroscopic characteristics

In the present study, castor oil (CO) was modified by epoxidation, transesterification, and acrylation processes. In situ epoxidation method was used to prepare epoxidized castor oil (ECO) in acetic acid with hydrogen peroxide in the presence of Seralite SRC-120 catalyst. Transesterified epoxidized castor oil was synthesized from the reaction of methanol in the presence of sodium methoxide catalyst. The acrylated epoxidized castor oil was synthesized from the reaction of ECO with acrylic acid containing hydroquinone. Chemical structures of modified CO were analyzed by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectra analysis.     

Theoretical Study of the Water-Gas Shift Reaction Catalyzed by Tungsten Carbonyls

A density functional theory calculation has been carried out to investigate the mechanism of W(CO)₆ and W₂(CO)₁₀ catalyzed water-gas-shift reaction (WGSR). The calculations indicate that the bimetallic catalyst (W₂(CO)₁₀) would be likely to be more highly active than the mononuclear metal-based catalyst (W(CO)₆) due to the possibility of metal–metal cooperativity in reducing the barriers for the WGSR. The energetic span model is a tool to compute catalytic turnover frequencies (TOFs) which is the traditional measure of the efficiency of a catalyst. The one with the highest efficiency usually gives the highest TOF. The bimetallic catalyst (W₂(CO)₁₀) exhibits high catalytic activity towards WGSR due to the highest value of the calculated TOF (3.62 × 10^?12 s^?1, gas phase; 8.74 × 10^?15 s^?1, solvent phase⁾, which is higher than the value of TOF (8.96 × 10^?20 s^?1, gas phase; 3.96 × 10^?19 s^?1, solvent phase) proposed by Kuriakose et al. (Inorg Chem 51:377–385, 2012). Our results will be important for designing a better catalyst for the industrially important reaction.     

W(II)-catalyzed hydroarylation of bicyclo[2.2.1]hept-2-ene by simple arenes

The tungsten(II) carbonyl compound (CO)₄W(μ-Cl)₃W(SnCl₃)(CO)₃ has been found to be a very effective catalyst for the hydroarylation of bicyclo[2.2.1]hept-2-ene (norbornene) conducted in arene solution at room temperature. Norbornene adducts with benzene, toluene, para-xylene, and mesitylene have been isolated and their structures have been unambiguously established by means of ¹H and ¹³C NMR spectroscopy. On the basis of ¹H NMR monitoring of several catalytic reactions, a possible mechanism involving coordination of norbornene to the W(II) atom and its activation has been proposed.     

Epoxidation of propylene with hydrogen peroxide catalyzed by heteropolyphosphatotungstate

The epoxidation of propylene with hydrogen peroxide catalyzed by a reaction-controlled phase transfer catalyst (RCPT) composed of quaternary ammonium heteropolyoxotungstates in acetonitrile medium is studied. The influence of several factors on the reaction is studied, such as the reaction temperature, the effect of H₂O amount, the reaction time, the effect of the catalyst amount, solvent effect and the recycle of the catalyst. Under mild conditions, H₂O₂ conversion is 98.6%, and propylene oxide (PO) selectivity based on H₂O₂ is 97.2%. During the epoxidation, the catalyst is dissolved in the solution. However, after H₂O₂ is used up, the catalyst can be recovered as a precipitate and can be recycled. We find that the recycled catalyst has similar catalytic activity as the fresh one.     

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.     

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.     

[Mn(TPPS)] immobilized on ionic liquid-modified silica as a heterogeneous and reusable catalyst for epoxidation of alkenes with NaIO<Subscript>4</Subscript> under ultrasonic irradiation

Effective epoxidation of alkenes using sodium periodate was accomplished with Manganese (III) tetrakis(p-sulfonatophenyl)porphyrin, [C₄₄H₂₆N₄O₁₂S₄Na₄], supported on ionic liquids-modified silica, Im-SiO₂, under ultrasonic irradiation conditions is reported. This heterogeneous catalyst, [Mn(TPPS)@SiO₂-Im] was characterized by elemental analysis, scanning electron microscopy (SEM), FT-IR and UV–Vis spectroscopic methods. The synthesized hybrid catalyst was applied for efficient epoxidation of various alkenes with sodium periodate in acetonitrile under ultrasonic irradiation conditions. This solid catalyst can be easily recovered by simple filtration and reused several time without apparent loss of its catalytic activity.     

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.