Activity In Epoxidation Of Olefins Research Articles

A novel mixed azido/phenoxido bridged 1D CuII coordination polymer containing o-vanillin-based compartmental ligand: Synthesis, magnetism, phenoxazinone synthase and catalytic activity in epoxidation of alkenes

A novel 1-D coordination polymer, formulated as [Cu2(L)(N3)3]·H2O (1), has been synthesized by reacting the Schiff base ligand, 2-methoxy-6-((2-(2-hydroxyethylamino)ethylimino) methyl)-phenol (HL), with copper(II) chloride dihydrate in the presence of sodium azide. The X-ray structural analysis shows that compound 1 consists of tetranuclear [Cu2(L)(N3)3]2 units bearing a central double asymmetric μ1,1-N3 bridge and terminal mixed µ1,1-N3/phenoxido bridges that are linked via a double µ1,1,3-N3 bridge forming a 1-D network. The magnetic properties of 1 show the presence of ferromagnetic Cu···Cu interactions through the central double μ1,1-N3 bridge (J1 = 81.7(3) cm−1) coexisting with antiferromagnetic Cu···Cu interactions through the double µ1,1-N3/phenoxido bridge (J2 = –62.3(4)cm−1). Additionally, there is a very weak antiferromagnetic interaction (zJ = –0.12(2) cm−1) through the asymmetric µ1,1,3-N3 bridge connecting the tetranuclear units. Using o-aminophenol (OAP) as a substrate, the phenoxazinone synthase-like catalytic activity of the CuII coordination polymer 1 has been studied. The compound efficiently catalyzes the aerobic oxidation of o-aminophenol in DMF medium with a turnover number Kcat = 31.69 h−1. Moreover, 1 has been used as an active catalyst for the epoxidation of cis-cyclooctene, as a model alkene, with tert-butyl hydroperoxide (TBHP), showing an excellent epoxide yield and selectivity in CHCl3 under reflux conditions. To enlarge the scope of the reaction, the efficacy of the catalytic method has also been investigated in the epoxidation of some other substituted alkenes.

Synthesis of Molybdenum Chelate-Bonded Fe3O4 Nanoparticles and Their Efficient Catalytic Activity in Epoxidation of Alkenes

Synthesis of Molybdenum Chelate-Bonded Fe3O4 Nanoparticles and Their Efficient Catalytic Activity in Epoxidation of Alkenes

Lamellar porous mo-modified carbon nitride polymers photocatalytic epoxidation of olefins

Abstract A lamellar porous Mo-modified carbon nitride polymers (CN-Mo) was successfully prepared by a simple bottom-up method, which involves molecule self-assembly by hydrogen bonding between uracil and melamine. Analysis Results of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectra (XPS) show that Mo element has been doped in the skeleton of carbon nitride. The optical characterization results of the as-prepared photocatalysts show that, CN-Mo has a suitable band structure that can promote the separation of carriers and expands the absorption of light. Compared with CN, CN-Mo has better photocatalytic activity for epoxidation of olefins. When the mass value (relative to melamine) of ammonium molybdate tetrahydrate is 2 %, the photocatalytic efficiency is the best for the epoxidation of styrene. And the conversion rate of styrene reaches 38.4 % and the selectivity of styrene oxide is up to 83.2 %. In addition, it can maintain the better photocatalytic performance for the epoxidation of styrene after five reaction-regeneration cycles. This finding provides an effective development direction for photocatalytic olefins epoxidation under mild conditions.

Formation of β-Ga2O3 nanorings from metal–organic frameworks and their high catalytic activity for epoxidation of alkenes

β-Ga2O3 nanorings fabricated by structural transformation of concave Ga-MOF nanodisks exhibit high catalytic activity for epoxidation of alkenes.

Single-crystalline hierarchically-porous TS-1 zeolite catalysts via a solid-phase transformation mechanism

Abstract Hierarchically porous zeolites are a type of very hot catalyst with improved catalytic performances as compared with conventional microporous-only zeolites due to the improved mass transportation among the hierarchical meso/macropores, which are expected to be the next-generation catalysts for conversion of bulky molecules and/or polymers. Moreover, hierarchical zeolites with the single crystalline structure that is an identical registry of micropores within the entire particle identified the less pore blockage and less diffusion limitation compared to an aggregated structure of nano-zeolites. The developed synthetic methods were mostly conducted in a liquid-phase system and usually required expensive additives, such as silanes or mesoporogons, etc. Finding facile and cost-effective synthetic methods have been still challenging. Here, a facile and cost-effective strategy by controlling the growth/crystallization in a solidified hydrogel system was reported for the synthesis of Ti-containing MFI-type zeolites (TS-1) to simultaneously achieve hierarchical porosity, single-crystalline structure, and high catalytic performance in alkene oxidations. The synthesized zeolites were characterized by XRD, SEM, TEM, Nitrogen adsorption analysis, DRUV spectroscopy, IR spectroscopy, etc. The growth processes were also tracked and well-characterized. It was found that the solid-phase transformation mechanism was dominated for forming the hierarchical structure. This strategy could directly produce TS-1 with abundant intracrystalline continuous mesopores and large amounts of active framework titanium species, contributing to higher activity for epoxidation of alkenes compared to the traditional microporous-only TS-1 zeolites.

Synergistic catalysis by Mn promoted ceria for molecular oxygen assisted epoxidation

Mesoporous manganese doped cerium oxide catalysts were prepared by an inverse micelle method with different manganese loadings. These materials exhibited superior activity for epoxidation of alkenes with molecular oxygen. Highest active 10MnCe material showed an activity of 80 % conversion and >99 % selectivity for cyclooctene epoxidation. The fluorite crystal structure which facilitates the high oxygen mobility, low temperature reducibility, homogeneous distribution of manganese on ceria, nanoparticle nature, higher number of oxygen vacancies, low valent states of manganese and cerium, and the ability to generate reactive oxygen species of the manganese doped cerium oxide could be correlated to the high catalytic activity. The reaction followed first order kinetics with a rate constant of 0.31 h−1 at 100 °C, and the activation energy turned out to be 10.5 kJ/mol. The mechanistic study revealed that the reaction proceeds via a unique mechanism which involves in situ generated superoxide and singlet oxygen species.

Copper complex supported on hollow porous nanosphere frameworks with improved catalytic activity for epoxidation of olefins

Abstract An efficient heterogeneous catalyst has been synthesized by anchoring copper complex onto the salicylaldehyde-modified hollow porous nanosphere frameworks (SA-HPNFs-BA), in which SA-HPNFs were firstly prepared by using amino-functionalized HPNFs to react with salicylaldehyde. The final copper complex functionalized hollow porous nanosphere frameworks (Cu-HPNFs-BA) possess the high specific surface area, hierarchically micro-/mesoporous structure and robust organic frameworks. The prepared Cu-HPNFs-BA heterogeneous catalyst shows improved catalytic performance and good recycling stability in selective epoxidation of olefins.

Synthesis of dipyroromethanes in water and investigation of electronic and steric effects in efficiency of olefin epoxidation by sodium periodate catalyzed by manganese tetraaryl andtransdisubstituted porphyrin complexes

Condensation of pyrrole with various aldehydes in the presence of BF3•etherate as an acid catalyst in water provides good yield of some dipyrromethanes. Prolongation of the reaction time with aldehydes substituted by electron-donating (mesityl) or electron-withdrawing (2,6-dichlorophenyl) groups on the ortho positions of the phenyl did not lead to decomposition or scrambling. Manganese trans disubstituted porphyrin complexes which derive from various dipyrromethanes and manganese tetraaryl porphyrin complexes including various substituents with different steric and electronic properties show good catalytic activity in epoxidation of alkenes by NaIO4in the presence of imidazole (ImH). The study of steric and electronic effects of the catalysts on the epoxidation of olefins shows that Mn-porphyrin complexes with more bulky and electron-releasing groups on meso phenyls could increase the epoxidation yield of most alkenes.

New Molybdenum(II) Complexes with α-Diimine Ligands: Synthesis, Structure, and Catalytic Activity in Olefin Epoxidation.

Three new complexes [Mo(η3-C3H5)Br(CO)2{iPrN=C(R)C5H4N}], where R = H (IMP = N-isopropyl 2-iminomethylpyridine), Me, and Ph, were synthesized and characterized, and were fluxional in solution. The most interesting feature was the presence, in the crystal structure of the IMP derivative, of the two main isomers (allyl and carbonyls exo), namely the equatorial isomer with the Br trans to the allyl and the equatorial with the Br trans to one carbonyl, the position trans to the allyl being occupied by the imine nitrogen atom. For the R = Me complex, the less common axial isomer was observed in the crystal. These complexes were immobilized in MCM-41 (MCM), following functionalization of the diimine ligands with Si(OEt)3, in order to study the catalytic activity in olefin epoxidation of similar complexes as homogeneous and heterogeneous catalysts. FTIR, 13C- and 29Si-NMR, elemental analysis, and adsorption isotherms showed that the complexes were covalently bound to the MCM walls. The epoxidation activity was very good in both catalysts for the cis-cyclooctene and cis-hex-3-en-1-ol, but modest for the other substrates tested, and no relevant differences were found between the complexes and the Mo-containing materials as catalysts.

Pyrazine dicarboxylate-bridged arsenotungstate: synthesis, characterization, and catalytic activities in epoxidation of olefins and oxidation of alcohols.

A praseodymium(iii)-containing arsenotungstate K16H15Li7[Pr2(H2O)3(pzdc)As3W29O103]2·38H2O (1) (pzdc = pyrazine-2,3-dicarboxylic acid) was synthesized by a conventional aqueous solution method and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), and single crystal X-ray diffraction. Structural analysis revealed that compound 1 was constructed by two identical subunits {Pr2(H2O)3(AsW9O33)3W2O4} bridged together by two pzdc ligands. In addition, compound 1 could act as an efficient catalyst for the epoxidation of olefins and oxidation of alcohols with hydrogen peroxide (H2O2) as the oxidant. In particular, the turnover frequency (TOF) in the oxidation of 1-phenylethanol reached up to 10 170 h-1, which is higher than that of previously reported catalysts.

Two inorganic–organic hybrids based on a polyoxometalate: Structures, characterizations, and epoxidation of olefins

Two new inorganic–organic hybrids, [Co3(bpdo)6(H2O)4Cl2][SiW12O40]·H2O (Co-SiW) and [Ni3(bpdo)6(H2O)4Cl2][SiW12O40]·H2O (Ni-SiW) (bpdo = 4,4′-bis(pyridine-N-oxide)), were synthesized from the Keggin-type [SiW12O40] anion and Co(II) and Ni(II) under hydrothermal conditions, respectively, and characterized by elemental analyses, powder XRD, IR spectra, and single-crystal X-ray diffraction. The structural analysis indicates that the 1D chain is constructed from a POM-based half-cage as a secondary building block linked by bridging bpdo ligands. The zigzag chains further stack into a three-dimensional body with channels. The 3D network structure with amphiphilic cavities is shaped by electrostatic interactions through the planes, which has potential to allow molecules such as styrene and H2O2 ingress and egress. Both of the hybrids demonstrated catalytic activity for epoxidation of olefins, which was examined using styrene and aqueous hydrogen peroxide (30%) as oxidant in acetonitrile, along with Co-SiW and Ni-SiW in a heterogeneous manner at 60 °C. Moreover, the conversion of epoxidation reaction in a heterogeneous manner is close to that of homogeneous catalysis, while being conveniently recovered and steadily reused without change of catalyst structure after epoxidation reactions.

Immobilization of a Molybdenum Complex on Bipyridine-Based Periodic Mesoporous Organosilica and Its Catalytic Activity for Epoxidation of Olefins

The dichlorodioxomolybdenum(VI) complex (MoO2Cl2) is an efficient and low-cost homogeneous catalyst for a variety of organic reactions, but its activity usually decreases after immobilization on a solid support. This report describes the synthesis of heterogeneous Mo complex catalysts using a bipyridine-periodic mesoporous organosilica (BPy-PMO) as a solid chelating ligand and MoO2Cl2 as a precursor, and their catalysis in the epoxidation of olefins with tert-butyl hydroperoxide (TBHP). The MoO2Cl(OH) complex could be immobilized on trimethylsilylated BPy-PMO (BPy-PMO-TMS), which was confirmed by Fourier-transform infrared spectroscopy, Raman spectroscopy, and X-ray absorption fine-structure analysis. The Mo complex immobilized on BPy-PMO-TMS exhibited greater catalytic activity for the epoxidation of cis-cyclooctene compared with conventional heterogeneous Mo complex catalysts using mesoporous silica, polystyrene, and naked BPy-PMO as supports. A large amount (up to 0.72 mmol g–1) of the Mo complex could...

Cyclopentadienyl–Silsesquioxane Titanium Catalysts: Factors Affecting Their Formation and Activity in Olefin Epoxidation with Aqueous Hydrogen Peroxide

The reaction of titanium chlorosilyl‐substituted cyclopentadienyl (Cp) complexes, Ti(η5‐C5H3R′SiMe2Cl)Cl3 (R′ = H, 1b; SiMe3, 1c), with 1 equiv. of various silsesquioxane trisilanols, R7Si7O9(OH)3 (R = iBu, 2a; Ph, 2b), affords either corner‐capped Cp derivatives, Ti(η5‐C5H3R′SiMe2Cl)(R7Si7O12‐κ3O3) (R′ = H, R = iBu, 5a, Ph, 5b; R′ = SiMe3, R = iBu, 7a, Ph, 7b), or cyclopentadienyl–silsesquioxane complexes, Ti(η5‐C5H4SiMe2OR7Si7O11‐κ2O2)Cl (R′ = H, R = iBu, 6a, Ph, 6b; R′ = SiMe3, R = iBu, 8a, Ph, 8b), depending on the reaction conditions. In any case, upon heating, kinetic products 5 and 7 are transformed into the corresponding thermodynamic products 6 and 8, respectively. The electron‐donating ability of the Cp ring is a relevant controlling parameter: a strong π‐donor character facilitates the isomerization process. In addition, the nature of the silicon substituents in the silsesquioxane framework, the type of solvent, and the reaction temperature are also factors that significantly affect this process. Cyclopentadienyl–silsesquioxane complexes 6b and 8b are efficient and selective catalysts for epoxidation with aqueous hydrogen peroxide under mild conditions. Such a catalytic efficiency is attributed to the hydrophobic environment generated about the titanium atom by the Cp ring incorporated into the cyclopentadienyl–silsesquioxane ligand.

Hydrogen bond controlled formation of trans-dihydroxo porphyrinato platinum(IV) complexes: Synthesis, characterization and catalytic activity in olefin epoxidation

A number of trans-dihydroxo porphyrinato platinum(IV) complexes, [(porp)PtIV(OH)2] have been synthesized and characterized from their platinum(II)-porphyrin precursors by spectroscopic methods. The crystal structure of the platinum complex of trans-dihydroxo-meso-tetramesitylporphyrinato platinum(IV) meta-chlorobenzoic acid ([(TMP)PtIV(OH)2](m-CBA)2) has also been determined. The porphyrin periphery is planar and the platinum atom has a slightly distorted octahedral environment. It must be noted that there is a very strong O–H⋯O hydrogen bond between the hydrogen atoms of m-chlorobenzoic acids and the two hydroxo ligands coordinated to the platinum center. This crystal structure has been previously described by us as trans-dihydroxo-meso-tetramesitylporphyrinato platinum(VI) meta-chlorobenzoate ([(TMP)PtVI(OH)2](m-CB)2), but the spectroscopic data has been reinterpreted due to the contradictory +6 oxidation state for platinum. The UV–Vis and NMR spectroscopic data suggest that the porphyrin skeleton is similar to that of normal porphyrins and are also indicative of the +4 oxidation state for platinum. Cyclic voltammetry studies also indicate that PtIITMP can oxidize up to PtIV(TMP+) species via three successive one-electron oxidation steps. The results of DFT studies and NBO analysis confirm that platinum has +4 oxidation state in both [(TMP)Pt(OH)2](m-CBA)2 and [(TMP)Pt(OH)2](m-CB)2 complexes. The catalytic activity of these porphyrin complexes has been investigated for the oxidation of various alkenes in the presence of iodosylbenzene.

An environmentally friendly route for grafting of molybdenum carbonyl onto a diaminosilane-modified SBA-15 molecular sieve and its catalytic behaviour in olefin epoxidation

Molybdenum carbonyl (Mo(CO)6) grafted onto a diaminosiloxane functionalized SBA-15 surface and showed promising activity for epoxidation of olefins.

Olefin Epoxidation Catalyzed by cis‐Dioxdomolybdenum(VI) Complexes Containing Chiral Alkoxo‐Imino Ligands Derived from (+)‐α‐Pinene

AbstractNew chiral cis‐dioxidomolybdenum compounds [MoO2(acac)(RN,O)] [R = Bn (1), pic (2)] and [{MoO2(acac)}2{μ‐(O,N,N,O)}] (3) have been synthesized by treating [MoO2(acac)2] withthe corresponding enantiomerically pure alcohol‐iminocompounds derived from (+)‐α‐pinene modification, (RN,OH) (R = Bn, pic) and (HO,N,N,OH), respectively. Compound [MoO2Cl2(O,N,N,O)] (4) has also been prepared. All the compounds were fully characterized both in solution and in the solid state, including by single‐crystal X‐ray diffraction analysis of enantiomerically pure 3. DFT studies support the stereoselectivity of the synthesis of compound 3. Catalytic olefin epoxidation studies were performed with cis‐cyclooctene, (R)‐limonene, and trans‐β‐methylstyrene by using derivatives 1–4 as catalyst precursors and tert‐butyl hydroperoxide (TBHP) or H2O2 as oxidant. All the catalytic systems showed high chemoselectivity irrespective of the terminal oxidant used. The molybdenum compounds exhibited medium to high catalytic activity at mild reaction temperatures, but no substantial optical induction was observed. This study represents the first use of chiral monoacetylacetonato‐cis‐dioxidomolybdenum compounds as homogeneous olefin epoxidation catalysts.

Synthesis and characterization of supported heteropolymolybdate nanoparticles between silicate layers of Bentonite with enhanced catalytic activity for epoxidation of alkenes

A new heterogeneous catalyst (PVMo/Bentonite) consisting of vanadium substituted heteropolymolybdate with Keggin-type structure Na 5[PV 2Mo 10O 40]·14H 2O (PVMo) supported between silicate layers of bentonite has been synthesized by impregnation method and characterized using X-ray diffraction, Fourier-transformed infrared spectroscopy, scanning electron microscopy, UV–vis diffuse reflectance spectroscopy, transmission electron microscopy and elemental analysis. X-ray diffraction and scanning electron microscopy analysis indicated that PVMo was finely dispersed into layers of bentonite as support. The PVMo/Bentonite used as an efficient heterogeneous catalyst for epoxidation of alkenes. Various cyclic and linear alkenes were oxidized into the corresponding epoxides in high yields and selectivity with 30% aqueous H 2O 2. The catalyst was reused several times, without observable loss of activity and selectivity. The obtained results showed that the catalytic activity of the PVMo/Bentonite was higher than that of pure heteropolyanion (PVMo).

Effect of the conditions of preparing titanium-containing zeolite on its catalytic activity in the epoxidation of olefins with hydrogen peroxide

The results from systematic studies of the conditions for obtaining a titanium-containing zeolite and its catalytic activity in the liquid-phase epoxidation of olefins with an aqueous solution of hydrogen peroxide in a medium of methanol are described. The yield of olefin oxides was taken as a criterion of activity of the catalyst. The highest catalytic activity was found in the samples that had the initial molar ratio of tetrabutoxy titanium (TBOT) to tetraethoxysilane (TEOS) of 0.04–0.06 and the molar ratio of tetrapropylammonium hydroxide (TPAH) to TEOS of 0.25–0.5 and were subjected to a hydrothermal processing at 170°C for 40–60 h. The titanium-containing zeolite was rinsed either with demineralized water or with methyl alcohol. Calcination was performed at 550°C. The catalyst synthesized under optimum conditions allows us to derive olefin oxides with a yield of 90–95%, accompanied by the quantitative conversion of hydrogen peroxide.

Epoxidation of Various Functionalized Olefins by a Ti-MWW/H2O2 Catalytic System

Abstract The catalytic properties of Ti-MWW catalysts for the epoxidation of olefins with different functional groups using hydrogen peroxide as an oxidant were studied. Ti-MWW shows higher olefin conversion and epoxide selectivity than the conventional titanosilicate TS-1. Solvents influence the catalytic activity of Ti-MWW, and water is the best one in the epoxidation of ethyl acrylate and allyl acetate. The functional groups with high electrophilicity and adjacent to the C=C bonds retard the catalytic activity for olefin epoxidation.

Synthesis and characterization of complexes containing Ti–O–Si moieties. Catalytic activity in olefin epoxidation

Reaction of [Cp*TiMe3] with O(SiPh2OH)2 yields the titanium siloxide derivative [Cp*TiMe{(OSiPh2)2O}]. Complex reacts with H2O to yield the corresponding oxo-titanium derivative [(Cp*Ti{(OSiPh2)2O})2(micro-O)]. The molecular structure of complex has been established by X-ray diffraction. Complex reacts with triphenylsilanol to give the asymmetric titanium siloxide [Cp*Ti(OSiPh3){(OSiPh2)2O}]. Treatment of the dinuclear titanium compound [(Cp*TiCl2)2(micro-O)] with an equimolar amount of O(SiPh2OH)2 yields complex [(Cp*TiCl)2{micro-(OSiPh2)2O}(micro-O)] in which the disiloxide moiety is bridging two titanium atoms. The structure of has been determined by X-ray diffraction. Reaction of [Cp*TiMe3] with HOSiPh3 yields the titanium triphenylsiloxide [Cp*TiMe2(OSiPh3)]. Complex reacts with water to yield [{Cp*TiMe(OSiPh3)}2(micro-O)]. The triflate compound [Cp*Ti(OSiPh3)2(OTf)] can be prepared by reaction of with HOTf and triphenylsilanol. We have tested the catalytic activity of some of the complexes in the epoxidation of cyclohexene.