Olefin Epoxidation Reactions Research Articles

Investigating the Mukaiyama-type epoxidation reaction of alkenes with Cr(III) salophen catalysts: A confrontation between experiments and DFT calculations

This study aimed at the complete elucidation of the mechanism of the Mukaiyama-type alkene epoxidation reaction using the [(salophen)CrIIICl] precatalyst, by combining spectroscopic (UV–visible and EPR) studies, catalytic reactivity and quantum chemical modeling. These studies performed in parallel allowed us to propose a detailed reaction scheme, in which two consecutive active species incorporating both {salophen(CrV = O)} moieties were formed in situ, resulting in two distinct catalytic regimes.

High-electrophilic (SiO)2Nb(OH)(=O) sites confined in silanol defects over Nb-Beta zeolite for efficient cyclic alkene epoxidation reactions

Dealuminated Beta zeolite has a large amount of silanol defects on its interface, which provides an ideal place for embedding metal species and creating metal active sites in a confined microenvironment. The confined metal sites as well as their surroundings are closely related to the reactant activation and transient state achievement. Hence, unraveling the confined metal sites is of great significance for the catalytic reaction process. Herein, niobium species were incorporated into the silanol defects over dealuminated Beta zeolite with a facile dry impregnation method, co-grinding the niobium precursor with dealuminated Beta zeolite support. The successful incorporation of niobium into the silanol defects for 30Nb-Beta zeolite was verified by DRIFT, 1H MAS NMR, UV–Vis and UV-Raman characterizations. XAS characterization and DFT calculations further disclosed that the confined Nb species existed as (SiO)2Nb(OH)(=O), containing two Si−O−Nb bonds, one Nb=O bond as well as one Nb−OH bond. The synthesized 30Nb-Beta zeolite catalyst displayed a superior cyclohexene conversion of 51.1%, cyclohexene oxide selectivity of 83.1% as well as TOF value of 188.2 h−1 ascribed to the inherent electrophilicity of Nb(V) for confined (SiO)2Nb(OH)(=O) species as well as the low oxygen transfer energy barrier for NbV−OOH species. Furthermore, the prepared 30Nb-Beta zeolite can be effectively employed to other cyclic alkene epoxidation reactions.

Room-temperature olefin epoxidation reaction by two 2D cobalt metal-organic complexes under O2 atmosphere: coordination and structural regulation

Room-temperature olefin epoxidation reaction by two 2D cobalt metal-organic complexes under O2 atmosphere: coordination and structural regulation

Hydrophilic Ti-MWW for catalyzing epoxidation of allyl alcohol

Titanosilicates are widely applied in the alkene epoxidation reactions with high reaction rate and selectivity to desired products. Their catalytic performance depends on the structure topology, the micro-environment of Ti active sites, and the hydrophobicity/hydrophilicity of zeolite framework. Herein, we focus on a hydrophilic substrate of allyl alcohol (AAL) and investigated catalytic performance of four titanosilicates (TS-1, Ti-MOR, Ti-MWW, and Re-Ti-MWW) in the AAL epoxidation reaction with hydrogen peroxide as the oxidant. Among them, Re-Ti-MWW, synthesized via the post-modification of Ti-MWW with piperidine, exhibited the highest activity. Moreover, the preferred solvent changed from MeCN for Ti-MWW to H2O for Re-Ti-MWW. The relative diffusion rate of AAL over Re-Ti-MWW was up to 466 × 10-7 s-1, much larger than those of other zeolites. The higher diffusion rate of Re-Ti-MWW was probably derived from the higher framework hydrophilicity as revealed by the smaller water contact angle of Re-Ti-MWW compared to the other zeolites, which contributed to the high activity in AAL epoxidation. In the continuous slurry reactor, Re-Ti-MWW achieved a high catalytic lifetime of 163 h, with the selectivity of desirable glycidol product maintained at > 97% in the H2O solvent system, showing high potential as an industrial catalyst for the AAL epoxidation reaction.

Palladium-catalyzed epoxidation of olefins using electrophiles as oxidizing agents

The development of palladium-catalysed olefin epoxidation reactions using electrophilic reagents as oxidants: modular synthesis of oxazolines. The efficient synthesis of esters, alcohols and halogen-containing products was achieved.

Dual-Ligand Strategy for the Design and Construction of a Cd-Zn Heterometallic Metal-Organic Framework by One-Pot Synthesis as a Heterogeneous Catalyst for the Epoxidation Reaction of Olefins.

The use of metal-organic frameworks (MOFs) as catalysts is reported in various industrial applications. In contrast to monometallic MOFs, heterometallic MOFs with mixed organic ligands showed enhanced catalytic properties. The catalytic properties of heterometallic MOFs can be enhanced by generating defects and the synergistic effect between the two heterometals at secondary building units. By using a solvothermal technique, a Cd-Zn heterometallic MOF with a new morphology, [Cd2Zn(DPTTZ)0.5(OBA)3(H2O)(HCOOH)] (IUST-4) [DPTTZ = 2,5-di(4-pyridyl)thiazolo[5,4-d]thiazole, OBA = 4,4'-oxybis(benzoic acid)], was synthesized via a mixed-ligand strategy and characterized by single-crystal and powder X-ray diffraction, Fourier transform infrared spectroscopy, elemental analysis, and thermogravimetric analysis. X-ray crystallographic analysis showed that IUST-4 is a neutral 3D metal-organic framework crystallized in the monoclinic system with space group C2/c. In this study, the catalytic properties of IUST-4 for the epoxidation of cyclooctene were investigated. IUST-4 was selected as the optimal catalyst for epoxy product production due to its high selectivity and yield. Moreover, the catalytic performance of IUST-4 was maintained despite five recycling cycles without significant degradation. The epoxidation of cyclooctene with IUST-4 has several advantages, including good selectivity, easy recovery, and short-time reaction.

Self-adaptive Metal-Organic Framework Assembles Di-iron Active Sites to Mimic Monooxygenases.

Despite significant efforts, it remains a challenge to design artificial enzymes that can mimic both structures and functions of natural enzymes. Here, we report the post-synthetic construction of binuclear iron catalysts in MOF-253 to mimic natural di-iron monooxygenases. The adjacent bipyridyl (bpy) linkers in MOF-253 can freely rotate to form the [(bpy)FeIII(μ2-OH)]2 active site in a self-adaptive fashion. The composition and structure of the [(bpy)FeIII(μ2-OH)]2 active sites in MOF-253 were characterized by a combination of inductively coupled plasma-mass spectrometry, thermogravimetric analysis, X-ray absorption spectrometry, and Fourier-transform infrared spectroscopy. The MOF-based artificial monooxygenase effectively catalyzed oxidative transformations of organic compounds, including C-H oxidation and alkene epoxidation reactions, using O2 as the only oxidant, which indicates the successful recapitulation of the structure and functions of natural monooxygenases using readily accessible MOFs. The di-iron system exhibited at least 27 times higher catalytic activity than the corresponding mononuclear control. DFT calculations showed that the binuclear system had a 14.2 kcal/mol lower energy barrier than the mononuclear system in the rate-determining C-H activation process, suggesting the importance of cooperativity of the iron centers in the [(bpy)FeIII(μ2-OH)]2 active site in the rate-determining step. The stability and recyclability of the MOF-based artificial monooxygenase were also demonstrated.

Synthesis and Characterization of New Lutidinium Ionic Liquid-Supported Vanadylsalicylaldoxime Complex for Catalytic Application in Epoxidation Reaction.

A new chelating task-specific ionic liquid (TSIL), lutidinium-based salicylaldoxime (LSOH), and its square pyramidal vanadyl(II) complex (VO(LSO)2 ) have been successfully synthesized and structurally characterized using elemental (CHN), spectral, and thermal analyses. The catalytic activity of the lutidinium-salicylaldoxime complex (VO(LSO)2 ) in the alkene epoxidation reactions was studied under various reaction conditions, such as solvent effect, alkene/oxidant molar ratio, pH, reaction temperature, reaction time, and the catalyst dose. The results demonstrated that the CHCl3 solvent, 1 : 3 of the cyclohexene/H2 O2 ratio, pH 8, temperature of 340 K, and catalyst dose of 0.012 mmol are assigned as the optimum conditions for achieving maximum catalytic activity for VO(LSO)2 . Moreover, the VO(LSO)2 complex has the potential for application in the effective and selective epoxidation of alkenes. Notably, under optimal VO(LSO)2 conditions, cyclic alkenes convert more efficiently to their corresponding epoxides than linear alkenes.

Seed-Assisted Synthesis of Hierarchically Structured Nano-Sized Ti-β Zeolites for the Efficient Epoxidation Reaction of Alkenes.

The development of nano-sized titanosilicate zeolites with hierarchical structures is crucial in promoting the efficient epoxidation of alkenes. In the present work, nano-sized hierarchical Ti-β (*BEA) zeolites with high crystal yield are prepared by a one-pot nanoseed-assisted approach. The influence of seed size on the resultant Ti-β zeolites is investigated by complementary characterizations, including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption/desorption, UV-vis diffuse reflectance spectroscopy (DRS), and UV Raman spectroscopy. The possible process for the formation of hierarchical Ti-β nanocrystals with the assistance of nanoseeds in the synthesis gel is proposed. Consequentially, the nano-sized hierarchical material prepared by the nanoseed-assisted method shows excellent mass transportation and accessibility to active sites by reducing particle size and constructing hierarchical porosity, hence showing a remarkably enhanced catalytic activity and selectivity in the epoxidation reaction of alkenes. This work will shed light on the efficient preparation of nano-sized titanosilicate zeolites.

Self-assembly of polyoxometalate clusters into two-dimensional clusterphene structures featuring hexagonal pores.

Two-dimensional (2D) structures have been shown to possess interesting and potentially useful properties. Because of their isotropic structure, however, clusters tend to assemble into 3D architectures. Here we report the assembly of polyoxometalate clusters into layered structures that feature uniform hexagonal pores and in-plane electron delocalization properties. Because these structures are 2D and visually reminiscent of graphene, they are referred to as 'clusterphenes'. A series of multilayer and monolayer clusterphenes have been constructed with 13 types of polyoxometalate cluster. The resulting clusterphenes were shown to exhibit substantially improved stability and catalytic efficiency towards olefin epoxidation reactions, with a turnover frequency of 4.16 h-1, which is 76.5 times that of the unassembled clusters. The catalytic activity of the clusterphenes derives from the electron delocalization between identical clusters within the 2D layer, which efficiently reduces the activation energy of the catalytic reaction.

TiO2 supported cobalt oxide for olefin epoxidation reaction - characterization, catalytic activities and mechanism - using a DFT model.

Metal oxide catalysts are known to trigger C-H bond activation selectively, indicating their suitability for olefin epoxidation. Nano-structured Co3O4 supported on TiO2 was prepared for selective epoxidation of a number of olefins under optimized reaction conditions. An appropriate synthetic procedure yielded a catalytic material (Co-Ti (NP)HT) with desired crystal size and interface conditions. Incorporation of Co into the Ti matrix resulted in an enhancement in the specific surface of Ti-Co nanoparticles (77.93 m2 g-1). XPS measurements evaluated the surface cobalt atom concentration (5.77%) in Ti-Co(NP)HT, indicating more dispersion of cobalt oxide species. Catalytic application of the material, using various olefins (under optimized reaction conditions) shows higher conversion (>85%) in a 6-h time interval. The substrate : oxidant (H2O2) concentration in an optimized molar ratio of 1 : 2 shows high olefin conversion for the formation of olefin oxide. The reactivity of olefins was found to be in the order: cyclohexene > methylstyrene > styrene > chlorostyrene > p-nitrostyrene. A DFT model compared the HOMO-LUMO energies of styrene and its substituted forms. The reusability of Ti-Co (NP)HT tested up to four continuous cycles of batch operations indicates a negligible loss (0.25-0.30%) of catalytic activity.

Aerobic epoxidation of olefins by carboxylate ligand‐based cobalt (II) compound: synthesis, X‐ray crystallography, and catalytic exploration

AbstractA new quinoline carboxylate‐based cobalt (II) metal compound, [Co (HL1)2(H2O)4] (1) (H2L1 = 2‐hydroxyquinoline‐4‐carboxylic acid) has been hydrothermally synthesized, and fully characterized by single‐crystal X‐ray diffraction, powder X‐ray diffraction, Fourier‐transform infrared (FT‐IR), elemental and thermo‐gravimetric analysis. Compound 1 shows high thermal stability up to ~300°C. Single‐crystal X‐ray diffraction study of 1 exhibited monomeric structure experiences further stabilized in solid state through different non‐covalent interaction, for example, H‐bonding and π···π stacking interaction and extended to 3D supramolecular H‐bonded network. Compound 1 efficiently catalyzes epoxidation reactions of olefins under homogeneous conditions using molecular oxygen as an oxidizer. Another reported quinoline carboxylate‐based nickel (II) monomer [Ni(L2)2(H2O)2] (2) (HL2 = thiazole‐4‐carboxylic acid) has been synthesized and characterized to compare it with compound 1 towards aerobic epoxidation reactions, where 1 comes as superior.

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.

Exceptional Catalytic Activity of Cu−Zn/ZrO2 Mixed Metal Oxide towards the Oxidation Reaction

AbstractHerein, we report the catalytic activity of the copper and zinc doped ZrO2‐based mixed metal oxide system towards the oxidation reaction. To study this attribute, different weight % loadings of copper and zinc supported on zirconia catalysts were synthesized by co‐precipitation followed by the hydrothermal method. The synthesized catalysts were characterized by various physicochemical methods. X‐ray analysis revealed that mainly cubic zirconia (111) planes were formed, and up to 0 to 25 wt.% Cu and Zn were doped in the zirconia lattice. Also, elemental mapping revealed uniform dispersion of Cu, Zn, Zr, and O elements. The catalytic activity of the synthesized catalyst was studied for olefin epoxidation and alcohol oxidation reactions using aqueous tert‐butyl hydrogen peroxide as an oxidant. Among all the synthesized catalysts, 2 wt.% doping of 1 : 1 Cu: Zn on ZrO2 gave almost complete olefin conversion with the best selectivity towards epoxides under optimized reaction conditions. Furthermore, the selected catalyst showed excellent substrate scope for different olefins and alcohol oxidation. Also, the catalyst was successfully recycled up to five cycles without affecting the conversion and selectivity.

Nonheme manganese(III) complexes for various olefin epoxidation: Synthesis, characterization and catalytic activity

Three mononuclear imine-based non-heme manganese(III) complexes with tetradentate ligands which have two deprotonated phenolate moieties, ([(X2saloph)Mn(OAc)(H2O)], 1a for X = Cl, 1b for X = H, and 1c for X = CH3, saloph = N,N-o-phenylenebis(salicylidenaminato)), were synthesized and characterized by 1H NMR, 13C NMR, ESI-Mass and elemental analysis. MnIII complexes catalysed efficiently various olefin epoxidation reactions with meta-chloroperbenzoic acid (MCPBA) under the mild condition. MnIII complexes 1a and 1c with the electron-withdrawing group -Cl and electron-donating group –CH3 showed little substituent effect on the epoxidation reactions. Product analysis, Hammett study and competition experiments with cis- and trans-2-octene suggested that MnIV = O, MnV = O, and MnIII-OOC(O)R species might be key oxidants in the epoxidation reaction under this catalytic system. In addition, the use of PPAA as a mechanistic probe demonstrated that Mn-acylperoxo intermediate (MnIII-OOC(O)R) 2 generated from the reaction of peracid with manganese complexes underwent both the heterolysis and the homolysis to produce MnV = O (3) or MnIV = O species (4). Moreover, the MnIII-OOC(O)R 2 species could react directly with the easy-to-oxidize substrate to give epoxide, whereas the species 2 might not be competent to the difficult-to-oxidize substrate for the epoxidation reaction.

Simultaneous oxidative and reductive reactions in one system by atomic design

Single-atom catalysts often exhibit unexpected catalytic activity for many important chemical and biological reactions with respect to their bulk counterparts, and have been recognized as potential substitutes for natural enzymes. Here we report a biomimetic composite, yolk–shell Pd1@Fe1, that features two compatible single-atom systems with atomically dispersed Fe1 sites in a N-doped carbon shell and Pd1 sites in a yolk derived from a metal–organic framework. Directly utilizing the O2 and H2 sources generated on-site from the electrocatalytic overall water splitting, the as-synthesized yolk–shell Pd1@Fe1 could simultaneously catalyse nitroaromatic hydrogenation and alkene epoxidation reactions and lead to a cascade synthesis of amino alcohols. Our findings provide a versatile strategy to integrate different single metal sites within one system to allow the continuous and easy synthesis of complex compounds for various challenging reactions. Single-atom catalysts can exhibit improved catalytic performance with respect to their bulk counterparts. Now, the authors introduce a yolk@shell catalyst with spatially separated Pd and Fe single sites that simultaneously catalyse nitroaromatic hydrogenation and alkene epoxidation reactions, leading to a cascade synthesis of amino alcohols.

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.

Synthesis, Characterization, and Application of Oxo-Molybdenum(V)-Corrolato Complexes in Epoxidation Reactions.

Sharpless et al. have described, while performing the molybdenum-catalyzed epoxidation reaction of olefins using alkyl hydroperoxides, that the molybdenum-oxo moiety is an active catalytic species. Thus, continuous efforts have been made to synthesize molybdenum-oxo complexes of different ligand environments. While plenty of such works on molybdenum porphyrins are reported in the literature, related molybdenum corroles are very less reported. The synthesis and characterization of two new oxo-molybdenum(V)-corrolato complexes are described herein. Both the complexes have been fully characterized by several spectroscopic techniques in conjunction with single-crystal X-ray diffraction analysis. The efficacy of the oxo-molybdenum(V)-corrolato complexes for the catalytic epoxidation reaction of olefins with the help of hydroperoxides has also been explored. The catalytic application of oxo-molybdenum(V)-corrolato complexes in the epoxidation reaction has not been reported earlier. A mechanism has been proposed to explain the experimental findings.

Iron and manganese oxo complexes, oxo wall and beyond.

High-valent metal-oxo species with multiply-bonded M-O groups have been proposed as key intermediates in many biological and abiological catalytic oxidation reactions. These intermediates are implicated as active oxidants in alkane hydroxylation, olefin epoxidation and other oxidation reactions. For example, [FeivO(porphyrinato•-)]+ cofactors bearing π-radical porphyrinato•- ligands oxidize organic substrates in cytochrome P450 enzymes, which are common to many life forms. Likewise, high-valent Mn-oxo species are active for H2O oxidation in photosystem II. The chemistry of these native reactive species has inspired chemists to prepare highly oxidized transition-metal complexes as functional mimics. Although many synthetic Fe-O and Mn-O complexes now exist, the analogous oxo complexes of the late transition metals (groups 9-11) are rare. Indeed, late-transition-metal-oxo complexes of tetragonal (fourfold) symmetry should be electronically unstable, a rule commonly referred to as the 'oxo wall'. A few late metal-oxos have been prepared by targeting other symmetries or unusual spin states. These complexes have been studied using spectroscopic and theoretical methods. This Review describes mononuclear non-haem Fe-O and Mn-O species, the nature of the oxo wall and recent advances in the preparation of oxo complexes of Co, Ni and Cu beyond the oxo wall.

Solvent-Free Environmentally Benign Approach for the Selective Olefin Epoxidation Catalyzed by Mn(III)-Immobilized Mesoporous Nanoarchitectonics.

Immobilization of transition metal complexes at the surface of 2D-hexagonal functionalized SBA-15 material is one of the promising strategies in designing an efficient catalytic system for the olefin epoxidation reaction. Here we have immobilized Mn(III) on the Schiff-base anchore 2D-hexagonally ordered functionalised mesoporous SBA-15 material. Powder X-ray diffraction (PXRD), N₂-sorption and high resolution transmission electron microscopic (HRTEM) studies of the resulting SBA-15-SB-Mn material suggested 2D-hexagonally ordered porous nanostructure and X-ray photoelectron spectroscopy (XPS) analysis suggested the presence of surface bound Mn(III) species in this nanomaterial. This mesoporous material showed excellent performance in the selective catalytic oxidation of various alkenes to the corresponding epoxides in the presence of tert-butyl hydroperoxide (TBHP, 70% aqueous solution) as oxidant under solvent-free mild reaction conditions together with high recycling efficiency.