Catalytic Epoxidation Of Olefins Research Articles

Tandem catalytic efficient olefin epoxidation with integrated production of nicotinamide derivatives

Tandem catalytic efficient olefin epoxidation with integrated production of nicotinamide derivatives

Manifesting Direction-Specific Complexation in [HFIP-H·H2O2]-: Exclusive Formation of a High-Lying Conformation.

Size-selective, negative ion photoelectron spectroscopy in conjunction with quantum chemical calculations is employed to investigate the geometric and electronic structures of a protype system in catalytic olefin epoxidation research, that is, deprotonated hexafluoroisopropanol ([HFIP-H]-) complexed with hydrogen peroxide (H2O2). Spectral assignments and molecular electrostatic surface analyses unveil a surprising prevalent existence of a high-lying isomer with asymmetric dual hydrogen-bonding configuration that is preferably formed driven by influential direction-specific electrostatic interactions upon H2O2 approaching [HFIP-H]- anion. Subsequent inspections of molecular orbitals, charge, and spin density distributions indicate the occurrence of partial charge transfer from [HFIP-H]- to H2O2 upon hydrogen-bonding interactions. Accompanied with electron detachment, a proton transfer occurs to form the neutral complex of [HFIP·HOO•] structure. This work conspicuously illustrates the importance of directionality encoded in intermolecular interactions involving asymmetric and complex molecules, while the produced hydroperoxyl radical HOO• offers a possible new pathway in olefin epoxidation chemistry.

Styrene epoxidation catalyzed by polyoxometalate/quaternary ammonium phase transfer catalysts: The effect of cation size and catalyst deactivation mechanism

Catalytic epoxidation of alkenes is an important type of organic reaction in chemical industry, and the deep insight into catalyst deactivation will help to develop new epoxidation process. In this work, series of quaternary ammoniums bearing different cationic sizes, i.e. MTOA+ (methyltrioctylammonium, [(C8H17)3CH3N]+), HTMA+(hexadecyltrimethylammonium, [(C16H33)(CH3)3N]+) and DMDOA+ (dimethyldioctadecylammonium, [(C18H37)2(CH3)2N]+) were incorporated with polyoxometalate (POM) anions to prepare phase transfer catalysts (PTCs), which were used in the styrene epoxidations. Among them, (MTOA)3PW4O24 exhibits the best catalytic performance judged from the highest styrene conversion rate (52%) and styrene oxide selectivity (93%), during which the styrene epoxidation conditions were optimized. Meanwhile, the deactivation mechanism of this kind of PTCs was proposed firstly, i.e. in the case of low H2O2 content, the oxidant can only be used in the styrene epoxidation, in which the catalyst can transform into stable Keggin-type POM. But when the content of H2O2 is higher, the excess H2O2 can re-activate the Keggin-type POM into active (PW4O24)3− anions, which can trigger the ring-opening polymerization of styrene oxide. Consequently, the catalyst is deactivated by adhered poly(styrene oxide) irreversibly, which was determined by NMR spectra. In this situation, the active moiety {PO4[WO(O2)2]4}3− in phase-transfer catalytic system can break into some unidentified species with low W/P ratio with the presence of epoxides. This work will be beneficial for the design of new PTCs in alkene epoxidation in fine chemical industry.

Site-Selective Catalytic Epoxidation of Alkene with Tunable, Atomic Precision by Molecularly Imprinted Artificial Epoxidases.

Distinction of chemical functionality by their local chemical environment is a skill mastered by enzymes, evident from the selective synthesis, cleavage, and transformation of peptides, nucleic acids, and polysaccharides that abound with the same type of functional groups. In contrast, synthetic catalysts are generally better at differentiating functional groups based on their electronic and steric properties. Here we report artificial epoxidases prepared through molecular imprinting of surface-core doubly cross-linked micelles, followed by efficient functionalization of the imprinted site in the micellar core via photoaffinity labeling. The size and shape of the active sites are tuned by the modularly synthesized templates, with the oxygen-delivering peroxy acid group positioned accurately. These catalysts are used in epoxidation of alkene in water with hydrogen peroxide under mild conditions, without any additional additives. Most importantly, atomic precision is achieved in the catalysis and enables alkenes to be distinguished that differ in the position of the carbon-carbon double bond by a single carbon.

Epoxidation catalysts prepared by encapsulation of molybdenum hexacarbonyl in UiO-66(Zr/Hf)-type metal-organic frameworks

The confinement and catalytic behavior of Mo(CO)6 species inside UiO-66 (zirconium and hafnium) metal-organic frameworks (MOFs) have been investigated by means of multitechnique characterization and catalytic olefin epoxidation. Mo(CO)6 was encapsulated in nanocrystalline MOFs by solvothermal and vapor phase impregnation methods (STI and VPI, respectively), resulting in Mo loadings of 2.0–8.8 wt% (STI) or 15 wt% (VPI). Powder X-ray diffraction, SEM-EDS, N2 adsorption, FT-IR and 13C{1H} CP MAS NMR collectively confirmed immobilization within the pore spaces of the hosts, which maintained their bulk crystallinity and crystal morphologies. CO resonances in the 13C{1H} CP MAS NMR spectra were assigned to hexacarbonyl guest molecules located in the larger pore spaces, such as the octahedral cavities (for STI and VPI samples), and in more restricted environments such as the tetrahedral cavities (for the VPI sample). FT-IR spectra displayed the characteristic pattern of νCO stretching modes for an octahedral symmetry molecule slightly perturbed by interaction of one of the carbonyl groups with the MOF support. The spectra evidenced the formation of a weak hydrogen bonding interaction of the type μ3-OH···OCMo(CO)5 involving the μ3-OH groups that are exclusively present in the tetrahedral cavities of the UiO-66 structure. The Mo(CO)6 loaded MOFs are active and reusable pre-catalysts for cis-cyclooctene epoxidation, exhibiting excellent epoxide selectivity (up to quantitative epoxide yield within 1 h reaction) and tert-butyl hydroperoxide efficiency. Catalyst recycling and retention of structural integrity were demonstrated for UiO-66(Hf) loaded with 8.8 wt% Mo by the STI method. The UiO-66(Hf) host may be a better catalyst support than its Zr counterpart due its smaller crystallite size (≈100 nm) and higher defectivity. The substrate scope was broadened for Mo(8.8-STI)/Hf-MOF which promoted the epoxidation of biobased olefins (methyl oleate and dl-limonene) and oxidative dehydrogenation of cyclooctanol to cyclooctanone.

Nonheme Diiron Oxygenase Mimic That Generates a Diferric-Peroxo Intermediate Capable of Catalytic Olefin Epoxidation and Alkane Hydroxylation Including Cyclohexane.

Herein are described substrate oxidations with H2O2 catalyzed by [FeII(IndH)(CH3CN)3](ClO4)2 [IndH = 1,3-bis(2'-pyridylimino)isoindoline], involving a spectroscopically characterized (μ-oxo)(μ-1,2-peroxo)diiron(III) intermediate (2) that is capable of olefin epoxidation and alkane hydroxylation including cyclohexane. Species 2 also converts ketones to lactones with a decay rate dependent on [ketone], suggesting direct nucleophilic attack of the substrate carbonyl group by the peroxo species. In contrast, peroxo decay is unaffected by the addition of olefins or alkanes, but the label from H218O is incorporated into the the epoxide and alcohol products, implicating a high-valent iron-oxo oxidant that derives from O-O bond cleavage of the peroxo intermediate. These results demonstrate an ambiphilic diferric-peroxo intermediate that mimics the range of oxidative reactivities associated with O2-activating nonheme diiron enzymes.

Asymmetrical Gemini Surfactants Directed Synthesis Of Hierarchical ZSM‐5 Zeolites and Their Immobilization of Molybdenum Complex for the Catalytic Epoxidation of Alkenes

AbstractAn eco‐friendly strategy for the synthesis of highly ordered meso‐ and microporous zeolites is required both in academia and industry. Therefore, asymmetrical anionic‐nonionic gemini surfactants, polyoxyethylene laurinol ether sodium sulfoitaconate (Gemini‐n), have been designed, synthesized and used in the directed synthesis of hierarchical ZSM‐5 zeolites (HZSM‐5) by imparting substantial mesoporosity. The hydrothermal temperature, the amount of gemini surfactants and the crystallization time strongly affected the crystallization degree and the textural properties of the HZSM‐5. The tune of the porous size distribution (microporous to mesoporous) can be obtained by varying the number of the ethylene oxide units in the gemini surfactants. Besides, the use of these novel anionic‐nonionic gemini surfactants is an effective strategy to avoid phase‐separation. The existence of abundant hydroxyl groups on the surface of HZSM‐5 was used to immobilize molybdenum compound by the stable Mo−O bond. The complex with abundant intercrystal mesopores exhibited superior catalytic performance with high yield and selectivity for the epoxidation reactions of alkenes as compared to the conventional ZSM‐5. Moreover, the complex presented high catalytic ability after been reused for five times.

The Effect oftransAxial Isocyanide Ligands on Iron(II) Tetra‐NHC Complexes and their Reactivity in Olefin Epoxidation

AbstractThe performance oftransaxially substituted mono‐(2 a) and bis(tert‐butylisocyanide) (2 b) complexes derived from the highly active bio‐inspired iron(II) (pre‐ )catalyst2containing an equatorial macrocyclic tetraN‐heterocyclic carbene in homogenous olefin epoxidation catalysis is reported. H2O2is used as oxidant in combination with the Lewis acid Sc(OTf)3as additive resulting in a considerable improvement of catalytic activity. In contrast to other iron epoxidation catalysts, the introduction of π‐accepting isocyanide ligands does not improve the catalytic performance of2 aand2 bposed by cyclic voltammetry. However, besides their lower activity, a high temperature tolerance of both compounds is found as a unique feature for iron NHC epoxidation catalysts.

钛硅分子筛催化剂高效钛位点的理性构筑与调控及催化烯烃环氧化的性能

<p indent="0mm">With the continuous promotion of high-end strategy for chemicals, the titanium silicalite-1 (TS-1) has attracted wide attention due to its unique oxidizing ability. The TS-1 has widespread applications in a series of reactions such as olefin epoxidation, cyclohexanone ammoxidation, and phenol hydroxylation. Therefore, the TS-1 is labeled as a milestone in the field of molecular sieve catalysis. Rational design and precise construction of high-performance TS-1 are the key to catalyze olefin epoxidation. This article summarizes three strategies for constructing high-performance titanium sites in TS-1, which involves designing specific coordination forms of titanium sites at the atomic scale, adjusting the microenvironment of titanium sites on the interface, and improving the accessibility of titanium sites in the particle. Moreover, the action modes and reaction mechanisms of different strategies are elaborated in detail, and corresponding constructing methods and characterization means are summarized. Furthermore, the current challenges and future perspectives about high-performance titanium sites are further proposed.

Enhanced enantioselectivity in heterogeneous manganese-catalyzed asymmetric epoxidation with nanosheets modified amino acid Schiff bases as ligands by modulating the orientation and the arrangement order

Catalytic enantioselective epoxidation of olefins plays an important role in the production of optically-active epoxy. Transition-metal complexes prove efficient for the catalytic epoxidation of un-functionalized olefins by employing privileged chiral ligands with rotational symmetry and bulky substituents, which usually require complicated multistep synthesis and are often very expensive. Here, this work proposes an efficient strategy to promote the enantioselectivity of Mn(III)-catalyzed indene epoxidation, which simply utilizes the nanosheets of layered double hydroxides (LDHs) to modify α-amino acid derivatives as chiral ligands, achieving an enantioselectivity of more than 91.0%, much higher than that (<35%) in the previous reports using chiral ligands without any rotational-symmetry. By virtue of “flexible” interlayer spaces of LDHs, intercalated L-tert-leucine, L-valine, L-leucine, and L-phenylalanine anions have further been derived in situ to L-tert-leucine, L-valine, L-leucine, and L-phenylalanine Schiff base anions. Over the Mn(III) coordinated with L-phenylalanine Schiff base anion intercalated LDHs, an indene conversion of 81.0 ± 1.0%, a chem-selectivity of 89.0 ± 1.0%, and an enantiomeric excesses (ee) value of 94.5 ± 0.5% for (1S,2R)-1,2-epoxyindane have been afforded. The spatial effects of LDH nanosheets on the enantioselectivity have been investigated, focusing on the interlayer orientation and arrangement order of intercalated amino acid derivative anions. The strategy has been proved valid for the epoxidation of functionalized olefins, which is more challenging, including allylic alcohols, chalcone, and chromene derivatives.

Mesoporous Methyl-Functionalized Titanosilicate Produced by Aerosol Process for the Catalytic Epoxidation of Olefins

Titanosilicates (Ti-SiO2) are well-known catalysts for the epoxidation of olefins. Isolated Ti inserted in the silica framework in tetrahedral coordination are the active species. Recently, adjusting the hydrophobic/hydrophilic balance of such catalysts’ surfaces has appeared as a promising tool to further boost their performance. However, adjusting the hydrophobic/hydrophilic balance via a one-pot classical sol-gel generally leads to a decrease in the Ti dispersion and/or collapse of the pore network. To overcome this limitation, hydrophobic mesoporous Ti-SiO2 were here synthesized by aerosol-assisted one-pot sol–gel, which allowed the simultaneous control of their Ti loading, degree of methyl-functionalization, and textural properties. Methyl-functionalization was achieved by a partial substitution of tetraethoxy silane (TEOS) by methyltriethoxy silane (MTES) in different ratios. Solid-state 29Si-NMR, FTIR, TGA, and vapor-phase water adsorption showed that methyl moieties were effectively incorporated, conferring a hydrophobic property to the Ti-SiO2 catalysts. ICP-AES, DRUV, XPS, and N2 physisorption demonstrated that Ti dispersion and textural properties were both successfully preserved upon the incorporation of the methyl moieties. In the epoxidation of cyclooctene with tert-butyl hydroperoxide as oxidant, the hydrophobic Ti-SiO2 showed higher catalytic performance than pristine Ti-SiO2 prepared without MTES. In addition to disentangling the positive effect of adjusting the hydrophobic/hydrophilic balance of epoxidation catalysts on their performance, this contribution highlights the advantages of the aerosol procedure to synthesize mesoporous functionalized catalysts with very high dispersion of active sites.

Hierarchical Ti-beta with a three-dimensional ordered mesoporosity for catalytic epoxidation of bulky cyclic olefins

Hierarchical beta zeolites with a three-dimensionally ordered mesoporous-imprinted (3DOm-i) structure and post-synthetic Ti grafting for catalytic epoxidation of cyclic olefins.

A recyclable cobalt(iii)–ammonia complex catalyst for catalytic epoxidation of olefins with air as the oxidant

A recyclable [Co(NH3)6]Cl3complex was synthesized to catalyze the epoxidation of α-pinene. With air as the oxidant, [Co(NH3)6]Cl3obtained 97.4% conversion of α-pinene and 98.3% selectivity of epoxide.

Catalytic Consequences of Oxidant, Alkene, and Pore Structures on Alkene Epoxidations within Titanium Silicates

Ti atoms incorporated into the framework of zeolite *BEA (Ti-BEA) or grafted onto SBA-15 (Ti-SBA-15) catalyze alkene epoxidation with hydrogen peroxide (H2O2), t-butyl hydrogen peroxide (TBHP), or ...

Synthesis and X-ray crystal structure of a Molybdenum(VI) Schiff base complex: Design of a new catalytic system for sustainable olefin epoxidation

A targeted new dioxo molybdenum(VI) ONO Schiff base complex was prepared for catalyzing epoxidation of olefins in water. This complex was characterized by FT-IR, NMR, UV–Vis, and X-ray crystallography techniques. DFT calculations are additionally performed to find ground and transition states for finding electronic structure and UV–Vis assignment. Afterward, a new protocol was defined for sustainable catalytic epoxidation of olefin in water using this complex as a green catalyst, and also remarkable results are obtained, such as turn over number up to 1400.

Mixed tetradentate NHC/1,2,3-triazole iron complexes bearing cis labile coordination sites as highly active catalysts in Lewis and Brønsted acid mediated olefin epoxidation

Two bio-inspired non-heme iron complexes bearing mixed tetradentate N-heterocyclic carbene/1,2,3-triazole ligands with cis labile coordination sites are reported. The compounds are studied in olefin epoxidation catalysis using H2O2 as oxidant. Sc(OTf)3, HClO4 and HOAc are applied as additives resulting in significant improvement of catalytic performance. Under optimized conditions the most active catalyst exhibits activities of 76,000 turnovers per hour, which is the highest reported value for an iron(II) catalyst. The complexes reveal comparably high stability and enable the challenging epoxidation of functionalized olefins. These results prove 1,2,3-triazoles to be promising and tunable ligands for iron catalyzed oxidation reactions.

Bolaform surfactant-directed synthesis of TS-1 zeolite nanosheets for catalytic epoxidation of bulky cyclic olefins

Hierarchical TS-1 nanosheets were hydrothermally synthesized by using a bolaform surfactant as the structure-directing agent and exhibited improved catalytic performance and superior recyclability in the epoxidation of cyclohexene and cyclooctene.

Schiff base complexes of Mo(VI) immobilized on functionalized graphene oxide nano-sheets for the catalytic epoxidation of alkenes

Mo(VI) tetradentate Schiff base complexes were covalently immobilized onto chemically functionalized graphene oxide (GO) using 3-(tri-methoxysilyl) propylamine as a coupler. The resulting heterogeneous catalysts have been characterized by FTIR, DRS, XRD, SEM, TGA, and atomic absorption spectroscopy (AAS). These catalysts were applied in epoxidation of cyclooctene and other olefins. The catalytic procedures with all catalysts were optimized for different parameters such as oxidant, solvent and temperature. Recycling results indicated that the catalysts were highly stable and maintained activity and selectivity even after being used for five cycles.

Synthesis of GO-SalenMn and Asymmetric Catalytic Olefin Epoxidation

Graphene oxide (GO) was used as a catalyst carrier, and after the hydroxyl group in GO was modified by 3-aminopropyltrimethoxysilane (MPTMS), axial coordination and immobilization with homogeneous chiral salenMnCl catalyst were carried out. The immobilized catalysts were characterized in detail by FT–IR, TG–DSC, XPS, EDS, SEM, X-ray, and AAS, and the successful preparation of GO-salenMn was confirmed. Subsequently, the catalytic performance of GO-salenMn for asymmetric epoxidation of α-methyl-styrene, styrene, and indene was examined, and it was observed that GO-salenMn could efficiently catalyze the epoxidation of olefins under an m-CPBA/NMO oxidation system. In addition, α-methyl-styrene was used as a substrate to investigate the recycling performance of GO-salenMn. After repeated use for three times, the catalytic activity and enantioselectivity did not significantly change, and the conversion was still greater than 99%. As the number of cycles increased, the enantioselectivity and chemoselectivity gradually decreased, but even after 10 cycles, the enantiomeric excess was 52%, which was higher than that of the homogeneous counterpart under the same conditions. However, compared to fresh catalysts, the yield decreased from 96.9 to 55.6%.

Hydrothermally robust Ti/SiO2 epoxidation catalysts via surface modification with oligomeric PMHS

We investigate grafting of poly(methylhydrosiloxane) (PMHS) onto Ti/SiO2 catalysts for improving their robustness to water, using olefin epoxidation catalysis with organic hydroperoxide as oxidant as a relevant probe reaction. Our approach involves triggering catalyst deactivation with added water in the reactants as a means to simulate catalyst deactivation, thereby causing grafted Ti-site aggregation. When using harsh aqueous Soxhlet extraction conditions as a trigger for this aggregation, significant differences are observed via diffuse-reflectance UV–vis spectrscopy on samples before and after treatment, for Ti/SiO2 catalysts containing grafted PMHS. Not only was there a lack of appearance of red-shifted bands in the UV-Vis spectrum following Soxhlet extraction, the batch catalytic activity for catalysts before and after PMHS grafting remained virtually unchanged. This was in stark contrast to an unmodified Ti/SiO2 catalyst, which showed a more than 60% decrease in catalytic activity following Soxhlet extraction as a result of aggregation, as ascertained by red shifts in its UV–vis spectrum after Soxhlet extraction. Similar red shifts were also observed for a hydrophobically modified TMS Ti/SiO2 catalyst. However, when comparing these catalysts under more gentle olefin epoxidation catalysis conditions with added water in a flow reactor, it was more difficult to differentiate the TMS Ti/SiO2 and grafted PMHS catalysts. Both catalysts exhibited similar activity and selectivity after a prolonged time on stream, though the rate of initial deactivation in the latter was less pronounced. Altogether, our data demonstrate that grafted PMHS catalysts are positively differentiated from conventional catalysts based on either TMS surface modification or no surface modification, under conditions involving aggregation induced via extreme hydrothermal environmentst. Thus, we expect that PMHS grafting of Lewis acid catalysts can offer an alternative approach for endowing hydrolytic stability to such catalysts, as demonstrated here for Ti/SiO2 epoxidation catalysts.