Epoxidation Of Various Olefins Research Articles

Fabrication of Polyoxometalate-Based Metal-Organic Frameworks Integrating Paddlewheel Rh2(OAc)4 for Visible-Light-Driven Oxidative Coupling of Amines.

The development of visible-light-responsive, environmentally friendly, and reusable photocatalysts for organic oxidation reactions is of vital significance. Herein, four polyoxometalate-based metal-organic frameworks (POMOFs) were synthesized and systematically characterized by assembling the paddlewheel complex Rh2(OAc)4 and various polyoxometalates (POMs). Single-crystal X-ray diffraction analysis revealed that the four POMOFs were isomorphic and possessed rare structural features among the POMOFs, with POMs as nodes and Rh2(OAc)4 as linkers. As expected, the activities of the four POMOFs for the photocatalytic oxidative coupling of benzylamine were better than that of Rh2(OAc)4 or POMs individually, which was ascribed to the synergistic effect between them, and the intrinsic reasons for the difference in the activity were explained via electrochemical measurements. In particular, the product imine yield reached 96.1% with NaRh-SiW12 as the catalyst and a turnover number and a turnover frequency of 480.5 and 120.5 h-1, respectively, while the product yield remained as high as 92% after three repetitions, evidencing its high stability. Moreover, the higher activities of the four POMOFs for the selective epoxidation of various alkenes reaffirm the synergistic effect between Rh2(OAc)4 and POMs.

Oxido-Molybdenum(V) Corroles as Robust Catalysts for Oxidative Bromination and Selective Epoxidation Reactions in Aqueous Media under Mild Conditions

Two new meso-substituted oxido-molybdenum corroles were synthesized and characterized by various spectroscopic techniques. In the thermogram, MoO[TTC] (1) exhibited excellent thermal stability up to 491 °C while MoO[TNPC] (2) exhibited good stability up to 318 °C. The oxidation states of the molybdenum(V) were verified by electron paramagnetic resonance (EPR) spectroscopy and exhibited an axial compression with dxy1 configuration. Oxido-molybdenum(V) complexes were utilized for the selective epoxidation of various olefins with high TOF values (2066-3287 h-1) in good yields in a CH3CN/H2O (3:2, v/v) mixture in the presence of hydrogen peroxide as a green oxidant and NaHCO3 as a promoter. The oxidative bromination catalytic activity of oxido-molybdenum(V) complexes in an aqueous medium has been reported for the first time. Surprisingly, MoO[TNPC] (2) biomimics of the vanadium bromoperoxidase (VBPO) enzyme activity exhibited remarkably high TOF values (36 988-61 646 h-1) for the selective oxidative bromination of p-cresol and other phenol derivatives. Catalyst MoO[TNPC] (2) exhibited higher TOF values and better catalytic activity than catalyst MoO[TTC] (1) due to the presence of electron-withdrawing nitro groups evident from cyclic voltammetric studies.

Anchoring of a terpyridine-based Mo(VI) complex on manganese ferrite as a recoverable catalyst for epoxidation of olefins under solvent-free conditions

A magnetically separable heterogeneous nanocatalyst was obtained by anchoring a terpyridine-based Mo(VI) complex on modified MnFe2O4 nanoparticles and characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD) and diffuse reflectance spectroscopies (DRS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) analysis. The catalytic activity of the supported molybdenum based catalyst was evaluated in the selective epoxidation of various olefins (cyclooctene, limonene, 1-dodecane, 1-heptene, styrene, 1-indene, α-pinene, cyclohexene) with tert-butyl hydroperoxide (TBHP) as an oxidant under solvent-free conditions. This nanocatalyst was easily separated by using an external magnetic field and reused consecutively at least five times with no significant loss in selectivity and catalytic activity. The short reaction time, simple preparation, high conversion, good physicochemical stability and magnetic recycling of the catalysts are beneficial.

Electron Affinity and Electronic Structure of Hexafluoroacetone (HFA) Revealed by Photodetaching the [HFA]•- Radical Anion.

A great deal of effort has been focused on developing a metal-free catalytic system for epoxidation of unreactive alkenes. Fluoroketones are thought as remarkably promising catalysts for epoxidation reactions. The combination of fluorinated alcohols and catalytic amounts of hexafluoroacetone (HFA) gives a versatile and effective medium for epoxidation of various olefins with hydrogen peroxide. However, the fundamental physicochemical properties of HFA remained largely unclear, although they were very important to understand the related interactions. Here, we performed a joint study on the electron affinity and electronic structure of HFA employing negative ion photoelectron (NIPE) spectroscopy and quantum chemistry calculations. Two distinct bands with complicated vibrational progressions were observed in the 193 nm NIPE spectrum. The adiabatic/vertical detachment energies (ADE/VDE) were derived to be 1.42/2.06 and 4.43/4.86 eV for the ground singlet state and excited triplet state, respectively. Using the optimized geometries and vibrational frequencies of the anion and the neutral, the Franck-Condon factors were calculated for electron detachments to produce HFA in its lowest singlet and triplet states. Good agreements are obtained hereby for both bands between the experimental and calculated NIPE spectra, when taking into account combination vibrational excitations, unequivocally revealing that HFA possesses a singlet ground state with a giant singlet-triplet energy difference (ΔEST). The electron affinity (EA) and ΔEST of HFA were therefore determined to be EA = 1.42 ± 0.02 eV and ΔEST = -3.01 eV.

Visible-light assisted of nano Ni/g-C3N4 with efficient photocatalytic activity and stability for selective aerobic C−H activation and epoxidation

A selective, economical, and ecological protocol has been described for the oxidation of methyl arenes and their analogs to the corresponding carbonyl compounds and epoxidation reactions of alkenes with molecular oxygen (O2) or air as a green oxygen source, under mild reaction conditions. The nano Ni/g-C3N4 exhibited high photocatalytic activity, stability, and selectivity in the C−H activation of methyl arenes, methylene arenes, and epoxidation of various alkenes under visible- light irradiation without the use of an oxidizing agent and under base free conditions.

The direct assembly of metalloporphyrin and Mg–Al layered double hydroxides nanosheets: a highly efficient catalyst for the green epoxidation of olefins

Co 5,10,15,20-tetrakis(4-sulfonatophenyl) porphyrin (CoTPPS) anions were successfully immobilized into the lamellar space of Mg–Al LDH through the spontaneous flocculation method by using exfoliated LDH nanosheets and guest molecules as building blocks. A variety of techniques including XRD, IR, UV–Vis, SEM, TEM and TG–DSC have been applied to characterize the morphology and microstructure of the obtained hybrids. It was found that the ratio between the metalloporphyrin molecules and LDH nanosheets has an important effect on the structure of restacking products. The interlayer spacing determined from XRD result suggests that a perpendicular orientation of the CoTPPS anions in the lamellar space. The surface charge changes associated with the flocculation process were traced through zeta potential measurements. The immobilized CoTPPS could act as an efficient and reusable heterogeneous catalyst for selective epoxidation of various alkenes including different cycloalkenes, styrene derivatives and long-chain alkenes. Cyclohexene undergoes up to 99% conversion within 2 h and 90% selectivity with molecular oxygen as environmentally friendly oxidant and isobutyraldehyde as co-reductant at room temperature. The CoTPPS/LDH2.0 can be easily recovered and reused for at least 5 times without obvious decrease of activity. This work provides a facile route to synthesize a highly efficient catalyst for the green epoxidation of olefins.

Intercalated cobalt porphyrin between layered double hydroxide nanosheets as an efficient and recyclable catalyst for aerobic epoxidation of alkenes

Anionic cobalt tetrasulfonatophenyl porphyrin (CoTPPS) intercalated NiAl LDH has been prepared through the exfoliation/restacking route. The obtained hybrids were characterized by XRD, SEM, TEM, IR, UV–Vis and TG-DSC. The volume ratio between the metalloporphyrin solution and LDH nanosheets suspension on the structure of restacking products was investigated and CoTPPS/Ni-Al LDH3.0 was found to exhibit the highest crystallinity. The interlayer spacing determined by XRD shows that CoTPPS was intercalated into the hyroxylated layers of LDH by a perpendicular orientation. The catalytic performance of the obtained hybrid material was investigated in the green epoxidation of various alkenes with oxygen as oxidant and isobutyaldehyde as co-reagent. The immobilized Co porphyrin demonstrated great application potential in oxidative catalysis, exhibiting exceptional stability and catalytic activity in oxidation of various alkenes.

Immobilization of salen molybdenum complex on dendrimer functionalized magnetic nanoparticles and its catalytic activity for the epoxidation of olefins

A novel catalyst was prepared by the immobilization of salen molybdenum complex on dendrimer functionalized magnetic nanoparticles. Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), N2 adsorption-desorption isotherms, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM), inductively couple plasma atomic emission spectroscopy (ICP-AES), and elemental analysis were used to characterize the catalyst. The synthesized catalyst was highly active and selective for the epoxidation of various olefins in the presence of tert-butyl hydroperoxide (TBHP) as oxidant. Notably, the catalyst could be separated easily by applying an external magnet and recycled up to six cycles without significant decrease in catalytic activity and selectivity.

Copper(II) Schiff base complex immobilized on graphene nanosheets: a heterogeneous catalyst for epoxidation of olefins

The present paper describes the preparation and characterization of Cu(II) Schiff base complex immobilized onto graphene oxide. The structural and morphological characterization of the heterogeneous catalyst was carried out by different techniques such as Fourier transform infrared and diffuse reflectance UV–Vis spectroscopies, X-ray diffraction, thermogravimetric analysis, nitrogen adsorption–desorption, transmission electron microscopy, field emission scanning electron microscopy and inductively coupled plasma atomic emission spectroscopy. The catalytic activity of the heterogeneous catalyst was studied in the epoxidation of various alkenes using tert-butyl hydroperoxide as an oxidant and it showed high selectivity and catalytic reactivity. The graphene-bound copper Schiff base was successfully reused for several runs without significant loss in its catalytic activity.

4,6‐Diacetyl Resorcinol Based Vanadium(V) Complexes: Reactivity and Catalytic Applications

Four ONO donor ligands are isolated from the condensation of 4,6‐diacetyl resorcinol with isonicotinoyl hydrazide (H2dar‐inh, I), nicotinoyl hydrazide (H2dar‐nah, II), benzoyl hydrazide (H2dar‐bhz, III), and 2‐furoyl hydrazide (H2dar‐fah, IV) on refluxing in MeOH. The reaction of in situ generated aqueous K[H2VVO4] with ligands I–IV at neutral pH gives complexes [K(H2O)2][VO2(dar‐inh)] (1), [K(H2O)2][VO2(dar‐nah)] (2), [K(H2O)2][VO2(dar‐bhz)] (3), and [K(H2O)2][VO2(dar‐fah)] (4), respectively. The reaction of [VIVO(acac)2] (acac = acetylacetonato) with these ligands (I–IV) under aerobic conditions in methanol yields oxidomethoxidovanadium(V) complexes [VO(OMe)(MeOH)(dar‐inh)] (5), [VO(OMe)(MeOH)(dar‐nah)] (6), [VO(OMe)(MeOH)(dar‐bhz)] (7), and [VO(OMe)(MeOH)(dar‐fah)] (8). All the isolated complexes are characterized by elemental, thermal, electrochemical, and spectroscopic techniques [FTIR, UV/Vis, NMR (1H, 13C and 51 V NMR)], and single‐crystal X‐ray diffraction analysis (for 1, 6, 7, and 8). X‐ray analysis confirms the coordination of the ligands through Ophenolate, Nazomethine, and Oenolate to the metal center. In the molecular structure of [K(H2O)(EtOH)][VVO2(dar‐inh)] (abbreviated as 1a where one molecule of water is replaced by EtOH), water molecules act as bridges between two K+ ions and the complex shows a dimeric structure due to the presence of electrostatic interactions between V=O oxygen atoms with K+ ions. These complexes are active catalysts for the oxidative bromination of thymol in the presence of KBr, HClO4, and H2O2 and give 2‐bromothymol, 4‐bromothymol, and 2,4‐dibromothymol as major products. Complexes 1–4 were also tested as catalysts for the epoxidation of various alkenes (namely styrene, cyclohexene, cis‐cyclooctene, 1‐hexene, 1‐octene, cyclohexenone, and trans‐stilbene) with H2O2 in the presence of NaHCO3 as promoter, giving the corresponding epoxides selectively.

Synthesis, characterization and catalytic epoxidation properties of a new tellurotungstate(iv)-supported rhenium carbonyl derivative.

A monomeric tellurotungstate(iv)-supported rhenium carbonyl derivative: Na2H2[(CH3)4N]6[Te2W20O70{Re(CO)3}2]·20H2O (1) has been successfully isolated and structurally characterized by single crystal X-ray diffraction crystallography, IR and UV-Vis spectroscopy, thermogravimetric analysis, etc. In particular, complex 1 could act as a efficient and reusable heterogeneous catalyst for selective epoxidation of various alkenes including different cycloalkenes, styrene derivatives, internal and long-chain alkenes. For example, cis-cyclooctene undergoes up to 98.2% conversion and >99% selectivity at 75 °C in acetonitrile with 30% H2O2 as an oxidant. Additionally, the electrocatalytic property of 1 for NO2- reduction was also investigated.

New complexes of Ni(II) and Co(III) with a Schiff-base ligand derived from o-vanillin. Crystal structure, magnetic and catalytic properties of a dissymmetric binuclear nickel(II) complex

A binuclear complex, [Ni2L2(NO3)(H2O)(CH3CN)]ClO4·CH3CN (1), has been obtained using a Schiff-base ligand (HL) derived from o-vanillin and 4-(2-aminoethyl)morpholine. The crystal structure of 1 has been solved. Both Ni(II) ions are hexacoordinated, but they display different coordination spheres. The exchange interaction between the two nickel ions is antiferromagnetic (J = −7.9 ± 0.2 cm−1; H = −JS1S2), in line with the DFT calculations. Compound 1 has been tested as a catalyst in the epoxidation of various olefins. The reaction of the same ligand with a mixture of cobalt(II) perchlorate and nitrate affords a mononuclear Co(III) complex, [CoL2(H2O)]ClO4·CH3OH (2).

Extremely low loading of Ru species on hydroxyapatite as an effective heterogeneous catalyst for olefin epoxidation.

We report a new class promising heterogeneous catalyst for olefin epoxidation based on 0.05 wt% Ru species supported on hydroxyapatite, which was prepared through a simple cation-exchange process between RuCl3·nH2O and hydroxyapatite. The new catalyst showed high activity, excellent selectivity and good recyclability for various olefins in the presence of molecular oxygen and iso-butyraldehyde as co-oxidants.

Heterogenized peroxopolyoxotungstate catalyst on the surface of clicked magnetite‐graphene oxide nanocomposite: Magnetically recoverable epoxidation catalyst

A new heterogeneous catalyst for the epoxidation of olefins was prepared by immobilization of peroxophosphotungstate anions on the surface of clicked magnetite‐graphene oxide as magnetically recoverable support. To prepare the heterogeneous catalyst, the clicked magnetite‐graphene oxide support was prepared by thiolene click reaction of thiol functionalized graphene oxide with vinyl modified magnetite nanoparticles. The tailored support was then modified with aminopropyl groups followed by electrostatic interaction with peroxophosphotungstate anions to achieve the desired heterogeneous catalyst. Characterization of the catalyst was performed by various physicochemical methods which confirmed the successful immobilization of peroxopolyoxotungstate species on the surface of clicked magnetite‐graphene oxide. Catalytic activity of the catalyst revealed its high catalytic activity and selectivity in the epoxidation of various olefins in the presence of H2O2 as green oxidant. This heterogeneous catalyst can be magnetically reused several times without significant loss of activity and selectivity.

Hydrothermal synthesis of a coordination polymer[CaII(5-AIP)(DMA)]n and its application in epoxidation of various organic substrates

A Ca(II) coordination polymer [CaII(5-AIP)(DMA)]n] (5-AIP=5-aminoisophthalic, DMA=dimethylacetamide) has been prepared by hydrothermal method using directional solvents like DMA. Single crystal X-ray analysis confirms the coordination of 5-AIP to the hepta coordinate metal centre along with DMA molecules. It crystallizes in orthorhombic space group Pna21 and has a polymeric structure containing CaII centers which adopt hepta coordinate pentagonal bipyramidal geometry. [CaII(5-AIP)(DMA)]n] has been successfully employed as catalyst in bicarbonate mediated epoxidation of various olefins.

Stable Copper Nanoparticle Photocatalysts for Selective Epoxidation of Alkenes with Visible Light

Selective epoxidation of various alkenes with molecular oxygen (O2) under mild conditions is a longstanding challenge in achieving syntheses of epoxides. Cu-based catalysts have been found to be catalytically active for selective epoxidations. However, the application of copper nanoparticles (CuNPs) for photocatalyzed epoxidations is encumbered by the instability of CuNPs in air. Herein we report that CuNPs supported on titanium nitride (TiN) without additional stabilizers not only are stable in air but also can catalyze selective epoxidation of various alkenes with O2 or even air as a benign oxidant under light irradiation. CuNPs remain in the metallic state due to the significant charge transfer that occurs between CuNPs and TiN. The epoxidation is driven by visible light irradiation at moderate temperatures, achieving good to high yields and excellent selectivity. The photocatalytic process is applicable to the selective epoxidation of various alkenes. In this photocatalytic system, reactant alkenes ch...

Clicked graphene oxide as new support for the immobilization of peroxophosphotungstate: Efficient catalysts for the epoxidation of olefins

Peroxophosphotungstate (PW) anions were successfully immobilized on the surface of clicked graphene oxides and used as heterogeneous catalysts for the epoxidation of various olefins using H2O2 as oxidant. Graphene oxide (GO) was functionalized with azide groups through both grafting and tethering methods Then, supported ionic liquids were formed on the surface of GO through the Cu (I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction. The clicked GO supported ionic liquids were used as appropriate supports for the immobilization of PW anions. Characterization of the prepared materials by various physicochemical methods showed that PW anions have been successfully immobilized on the surface of clicked GOs. Catalytic activities of these heterogeneous catalysts were evaluated in the epoxidation of olefins which showed that not only the catalysts are active, but also they could be reused several times without significant loss of their activities.

Metallophthalocyanine intercalated layered double hydroxides as an efficient catalyst for the selective epoxidation of olefin with oxygen

Varied metallophthalocyanine intercalated layered double hydroxides (LDHs) as bifunctional hybrid catalysts for selective epoxidation have been prepared and characterized. Systematic characterizations suggested the successful intercalation of the metallophthalocyanines into the interlayer of ZnAl LDHs. The synthesized hybrid exhibited excellent catalytic activity in the selective epoxidation of various olefins through O2/isobutaldehyde system. The basicity of the hybrid benefits to the selectivity of epoxide, and the bifunctional roles of the catalyst in the reaction have been discussed and verified by a series of controlled experiments. On the basis of obtained results, a probable mechanism of the epoxidation by the hybrid has been proposed and detailedly investigated. Under the catalysis of metallophthalocyanines intercalated LDHs in the presence of O2/isobutaldehyde, the production of epoxide undergoes two reaction paths. And two types of intermediates, namely acylperoxy radical and peroxyacid, are formed in the reaction, and the former is predominant.

Asymmetric Epoxidation of Olefins with H2O2 Catalyzed by a Bioinspired Aminopyridine N4 Iron Complex

AbstractAn iron complex with a chiral aminopyridine N4 ligand bearing strong electron‐donating and bulky morpholine groups on the ligand is synthesized and characterized. The iron complex serves to efficiently catalyze the asymmetric epoxidation of various olefins by employing aqueous hydrogen peroxide as the green oxidant, providing the corresponding epoxides in good to excellent yields and enantioselectivities (up to 93 % yield and 99.9 % ee). Owing to the introduction of morpholine functional groups on the ligand, the Fe‐catalyzed reaction can proceed with a catalytic amount of the carboxylic acid partner (3 mol %).

Synthesis, characterization and catalytic epoxidation properties of lanthanide-stabilized peroxoisopolytungstates.

A series of new lanthanide-containing peroxoisopolyoxotungstates, K6Na4[H32{Ln4(WO4)(H2O)16[W7O22(O2)2]4}3]·105H2O [Ln = CeIII (1), NdIII (2), SmIII (3), TbIII (4), ErIII (5)], have been successfully synthesized and structurally characterized. All polyanions [Ln(WO4)(H2O)16{W7O22(O2)2}4]14- are isostructural and consist of a central [Ln(WO4)(H2O)16]10+ cluster surrounded by four peripheral [W7O22(O2)2]6- units. They could act as efficient recyclable catalysts for the epoxidation of various alkenes including different cycloalkenes, styrene derivatives, internal and long-chain alkenes. Under optimal conditions, catalyst 2 displays the best catalytic activity for the oxidation of cyclooctene with high cyclooctene conversion (98.3%) and excellent selectivity (up to 99%) and could be reused for three cycles with a negligible decrease in reactivity.