A Theoretical Study of the Epoxidation of Olefins by Peracids

For the parent reacting system, HCOOOH + CH(2)=CH(2) --> HCOOH + ethylene oxide, the overall potential energy surface has been determined using ab initio methods. The oxygen-addition transition state is found to be remarkably similar to that deduced experimentally. The O-H bond is retained in the transition state. Reasonable kinetic isotopic effects are obtained theoretically. The transition state leads to an unprecedented transient intermediate. That intermediate is converted to a hydrogen-bonded system between ethylene oxide and formic acid. Substituent effects on transition-state geometries are small, but the effects on activation energies are large.     

Mycobacterium E3休止细胞催化烯烃立体选择性环氧化

初步研究了ＭｙｃｏｂａｃｔｅｒｉｕｍＥ３的生长和产酶特性，利用ＭｙｃｏｂａｃｔｅｒｉｕｍＥ３休止细胞催化烷羟化和烯烃环氧化，研究结果表明，烷烃不能被羟化，烯烃环氧化具有底物选择性，对烯丙基型底物ＸＣＨ２ＣＨ＝ＣＨ２（Ｘ＝Ｈ，Ｃｌ，Ｂｒ，ＯＨ）取代基大小显著性环氧化活性，ＭｙｃｏｂａｃｔｅｒｉｕｍＥ３中烯烃单加氧酶和另一种结构未知的酶的存在导致烯烃环氧化过程中存在环氧化物的立体选择性形成和非立体选择     

手性联萘酚配合物催化的缺电子烯烃不对称环氧化反应

缺电子烯烃的不对称环氧化反应是有机合成领域最具有挑战性的课题之一。手性联萘酚配体所修饰的催化剂是一种很优异的C2轴对称手性诱导源,可以催化各种α,β－不饱和羰基化合物如α,β－不饱和酮、α,β－不饱和羧酸脂等的不对称环氧化反应,具有良好的催化活性和对映选择性。本文对由手性联萘酚类配体所修饰的小分子催化剂、聚合物负载的催化剂和自负载催化剂在不饱和羰基化合物的催化不对称环氧化反应中的应用进行了综述,探讨了催化剂结构、配位金属原子、添加物、氧化剂、溶剂和反应温度等因素对手性联萘酚催化剂催化效能和对映选择性的影响。     

分子筛担载金催化剂催化烯烃环氧化制环氧化合物

烯烃的环氧化是工业上的重要反应之一，在众多的烯烃中，端烯尤其是直链端烯是相对较难氧化的一类。     

A New Generation of Titanosilicate Catalyst: Preparation and Application to Liquid-Phase Epoxidation of Alkenes

A novel titanosilicate with the MWW topology, Ti-MWW, has been prepared by direct hydrothermal synthesis using boric acid as a structure-supporting agent, and also by post-incorporation of tetrahedral Ti species into MWW silicalite through controlled structural conversions between three-dimensional crystalline silicalite and the lamellar precursor. Ti-MWW is further converted by delamination into a thin sheet material applicable to the reaction of bulky reactants. Both direct hydrothermal synthesis and postsynthesis methods make it possible to introduce a controllable amount of Ti species into the MWW structure. An acid treatment of uncalcined samples is essentially important for the removal of the extraframework octahedral Ti species located on the exterior layer surface. The catalytic properties of Ti-MWW have been compared with those of conventional titanosilicates (TS-1, TS-2, Ti-Beta, Ti-MOR, Ti-MCM-41, etc.) in the epoxidation of various alkenes with hydrogen peroxide. Hydrothermally synthesized Ti-MWW proves to be more effective in the epoxidation of linear alkenes including functionalized ones, and also exhibits considerable activity for cycloalkenes. Moreover, it shows a unique shape selectivity not shared with other titanosilicates in the epoxidation of cis/trans geometric alkene isomers. Postsynthesized Ti-MWW, nearly free of boron, catalyses the alkene epoxidation more effectively as a result of the tetrahedral Ti species different from those resulting from the direct synthesis, which turns out to be the most active epoxidation titanosilicate catalyst so far. Delaminated Ti-MWW, possessing an extremely open and accessible surface area but maintaining the basic structure of zeolite, catalyses the epoxidation of various cycloalkenes more actively than large pore titanosilicates including mesoporous Ti-MCM-41.     

离子液体中锰卟啉催化双氧水氧化烯烃的研究

研究了离子液体中Mn(TFPP)Cl(meso-tatrakis(pentafluoropheyl)porphinato)manganese(Ⅲ)cloride锰卟啉催化烯烃的氧化反应.在离子液体-CH2C12混合溶剂中,以价廉、环境友好的H2O2为氧源,考察了离子液体结构、反应条件等对环氧化反应的影响.当氧化剂/环己烯/催化剂/咪唑=450∶150∶1∶75(摩尔比)时,室温下,在MMISM-CH2Cl2的混合溶剂中,环己烯的转化率和环氧环己烷的选择性可分别达到94.8%和95.5%,远高于在纯CH2Cl2中的实验结果.并在最优反应条件下考察了该催化剂体系对烯烃底物的适用性.此外,反应结束后,产物可以由正己烷萃取出来,考察了混合溶剂中Mn(TFPP)Cl催化剂的重复使用情况.     

Kinetics and Mechanism of the Epoxidation of Alkyl-Substituted Alkenes by Hydrogen Peroxide, Catalyzed by Methylrhenium Trioxide

Epoxidations of alkyl-substituted alkenes, with hydrogen peroxide as the oxygen source, are catalyzed by CH(3)ReO(3) (MTO). The kinetics of 28 such reactions were studied in 1:1 CH(3)CN-H(2)O at pH 1 and in methanol. To accommodate the different requirements of these reactions, (1)H-NMR, spectrophotometric, and thermometric techniques were used to acquire kinetic data. High concentrations of hydrogen peroxide were used, so that diperoxorhenium complex CH(3)Re(O)(eta(2)-O(2))(2)(H(2)O), B, was the only predominant and reactive form of the catalyst. The reactions between B and the alkenes are about 1 order of magnitude more rapid in the semiaqueous solvent than in methanol. The various trends in reactivity are medium-independent. The rate constants for B with the aliphatic alkenes correlate closely with the number of alkyl groups on the olefinic carbons. The reactions become markedly slower when electron-attracting groups, such as halo, hydroxy, cyano, and carbonyl, are present. The rate constants for catalytic epoxidations with B and those reported for the stoichiometric reactions of dimethyldioxirane show very similar trends in reactivity. These findings suggest a concerted mechanism in which the electron-rich double bond of the alkene attacks a peroxidic oxygen of B. These data, combined with those reported for the epoxidation of styrene (a term intended to include related molecules with ring and/or aliphatic substituents) by B and by the monoperoxo derivative of MTO, suggest that all of the rhenium-catalyzed epoxidations occur by a common mechanism. The geometry of the system at the transition state can be inferred from these data, which suggest a spiro arrangement.     

Olefin Epoxidation by Methyltrioxorhenium: A Density Functional Study on Energetics and Mechanisms

A spiro attack on a peroxo group is calculated to be the preferred reaction pathway for olefin epoxidation with the catalytic system CH₃ReO₃/H₂O₂ (see picture). This finding is supported by density functional calculations on more than ten transition states for the most probable mechanisms. Hydration has significant effects on various reaction species: it stabilizes the intermediates and destabilizes, with one exception, the transition states.     

果糖衍生手性酮催化烯烃不对称环氧化反应的研究进展

综述了果糖衍生的手性酮催化烯烃不对称环氧化反应的发展及应用。参考文献34篇。     

Salen-decorated Periodic Mesoporous Organosilica: From Metal-assisted Epoxidation to Metal-free CO2 Insertion

We clicked a salen ligand onto a thiol-ethane bridged periodic mesoporous organosilica (Salen-PMO) using a photo-initiated thiol-ene click reaction. This process resulted in a covalently bonded salen ligand on the PMO material. The final BET surface area amounts 511 m²/g and the pore size diameter is approximately 7 nm. The functionalized PMO material showed an excellent carbon dioxide uptake capacity of 1.29 mmol/g at 273 K and 1 bar. More importantly, by coordinating a MoO₂²⁺ complex onto the Salen-PMO material, we obtained a heterogeneous catalyst with a good catalytic performance for the epoxidation of cyclohexene. The catalyst was highly reusable, as no decrease in its activity was observed for at least four runs (99% conversion). Finally, the metal-free Salen-PMO showed an exceptional catalytic performance in the cycloaddition of CO₂ to epoxides. The obtained results clearly demonstrate the versatility of the Salen-PMO material not only as metal-free catalyst but also as a support material to anchor metal complexes for specific catalytic applications. With the same catalytic platform, we were able to firstly create epoxides out of alkenes, and subsequently turn these epoxides into cyclic carbonates, consuming CO₂.     

Aerobic Epoxidation of Alkenes Catalysed by Cobalt(II) 1,1,1,5,5,5-Hexafluoroacetylacetonate or Cobalt(II) Benzoylacetonate

The aerobic epoxidation of terminal or electron deficient alkenes with an aldehyde does not proceed with cobalt(II) acetylacetonate but goes to completion with the cobalt(II) benzoylacetonate and cobalt(II) 1,1,1,5,5,5-hexafluoroacetylacetonate complexes.     

Asymmetric Michael Addition of Activated Alkenes to Nitro Alkenes Catalyzed by Organic Catalyst

Enantioselective Michael addition is one of the most powerfulbond-forming reaction in organic synthesis. [1] A mong the Michael acceptors, nitro alkenes are very attractive, because the nitro group is the most electron-withdrawing group known and it can serve as masked functionality to be further transformed after the addition has taken place. [2] Recently, asymmetric Michael reactions catalyzed by organic catalyst have draw much attention.[3]     

The Dirac Electron: From Quantum Chemistry to Holistic Cosmology

The Dirac equation, which was derived by combining the relativistic invariance condition with the quantum probability principle, showed its fecundity by explaining the half‐integer spin of fermions and by predicting antiparticles. In previous papers, we conjectured that the spinning motion of the electron was that of a massless charge moving at light velocity, this internal motion being responsible for the electron rest mass involved in external motions and interactions. Implications of this concept on basic properties such as time, mass, electric charge, and magnetic moment were investigated. The present paper is a recollection of these ideas aimed at their possible impact on quantum chemistry and holistic cosmology.     

Hydroformylation of Alkenes in a Planetary Ball Mill: From Additive‐Controlled Reactivity to Supramolecular Control of Regioselectivity

The Rh‐catalyzed hydroformylation of aromatic‐substituted alkenes is performed in a planetary ball mill under CO/H₂ pressure. The dispersion of the substrate molecules and the Rh‐catalyst into the grinding jar is ensured by saccharides: methyl‐α‐d ‐glucopyranoside, acyclic dextrins, or cyclodextrins (CDs, cyclic oligosaccharides). The reaction affords the exclusive formation of aldehydes whatever the saccharide. Acyclic saccharides disperse the components within the solid mixture leading to high conversions of alkenes. However, they showed typical selectivity for α‐aldehyde products. If CDs are the dispersing additive, the steric hindrance exerted by the CDs on the primary coordination sphere of the metal modifies the selectivity so that the β‐aldehydes were also formed in non‐negligible proportions. Such through‐space control via hydrophobic effects over reactivity and regioselectivity reveals the potential of such solventless process for catalysis in solid state.     

Titanium Salan Catalysts for the Asymmetric Epoxidation of Alkenes: Steric and Electronic Factors Governing the Activity and Enantioselectivity

A new insight into the highly enantioselective (up to >99.5 % ee) epoxidation of olefins in the presence of chiral titanium(IV) salan complexes is reported. A series of 14 chiral ligands with varying steric and electronic properties have been designed, and it was found that electronic effects modulate the catalytic activity (without affecting the enantioselectivity), whereas the steric properties account for the enantioselectivity of the epoxidation. Competitive oxidations of p‐substituted styrenes reveal the electrophilic nature of the oxygen‐transferring active species, with a Hammett ρ value of ?0.51; the enantioselectivity is unaffected by the electron‐donating (or withdrawing) ability of the p‐substituents. Mechanistic studies provide evidence in favor of a stepwise reaction mechanism: in the first (rate‐determining) stage, olefin most probably coordinates to the active species, followed by intramolecular enantioselective oxygen transfer. The enantioselectivity increases with decreasing temperature. The modified Eyring plots for the epoxidation of styrene and (Z)‐β‐methylstyrene are linear, indicating a single, enthalpy‐controlled mechanism of stereoselectivity, with ΔΔH^≠=?6.6 kJ mol^?1 and ?5.4 kJ mol^?1, respectively.     

Chiral Salen Manganese Complex Immobilized on SBA-15： A New Heterogenized Enantioselective Catalyst for the Epoxidation of Alkenes

Jacobsen‘s catalyst was immobilized onto SBA-15 by multi-step grafting, and this heterogenized catalyst exhibited comparable catalytic performance with the corresponding homogeneous counterpart for the epoxidation of alkenes, and the catalyst could be recycled effectively several times.     

Pyrazole-3-carboxylic Acid Manganese Complex: Syntheses and Its highly Efficient Heterogeneous Catalysis for the Epoxidation of Alkenes

One inorganic-organic hybrid manganese complex Mn(Hpca)2(phen)·3 H_2O(1) based on pyrazole-3-carboxylic acid(H2 pca) and phenanthroline(phen) has been synthesized and fully characterized by single-crystal X-ray diffraction(SXRD), powder X-ray diffraction(PXRD), infrared spectroscopy(IR), thermal gravity analysis(TGA) and elemental analyses. Complex 1 crystallizes in the monoclinic system, space group P2_1/c with Z = 4, a = 10.3170(9), b = 13.1061(12), c = 17.6919(15) ?, V = 2272.1(3) ?~3, F(000) = 1052, D_c = 1.495 g/cm~3, μ = 0.635 mm~(-1), the final R = 0.0428 and wR = 0.0853. In the crystal structure, the mononuclear Mn~(2+) center was coordinated by two Hpca-and one phen ligands, and shows a distorted {MnO_2N_4} octahedral coordination geometry. In the supermolecular structure, the independent units are entrained within several hexanuclear chair-like water clusters by the O-H···O and N-H···O hydrogen bonding interactions and finally form the three-dimensional framework. Notably, as a robust heterogeneous catalyst, complex 1 exhibits excellent catalytic performance in the epoxidation of alkenes with peroxyacetic acid as the oxidant(Conv. up to 97.7%, Sele. up to 98.9%). Additionally, the catalyst can be reused without losing its activity after three runs catalytic cycle.     

碳量子点阳离子表面活性剂的多功能性

碳量子点以其多彩的荧光及廉价而丰富的制备原料引起人们的广泛兴趣。至今,已有大量关于碳量子点制备及其荧光性能直接利用的文献报道。若采用恰当的方法对碳量子点进行化学修饰,则可以将其转化为实用的精细化学品,从而拓展碳量子点的应用领域。本文报道了一种碳量子点阳离子表面活性剂的制备方法。首先,乙二胺四乙酸、二乙胺及双氧水的混合水溶液经水热处理,获得碳量子点(以OX-CQDs表示),再以氯代正构十二烷对其进行季铵化修饰,获得新型碳量子点阳离子表面活性剂(以OX-CQDs-C₁₂H₂₅表示)。OX-CQDs-C₁₂H₂₅具有良好的降低水的表面张力和减小水接触角的能力,水的界面张力能降低至26.7 mN∙m⁻¹,其性能超过了一些新型的Gemini型阳离子表面活性剂;季铵化的修饰也大大提高了OX-CQDs对大肠杆菌的抑菌能力,低至0.41 mg∙mL⁻¹的OX-CQDs-C₁₂H₂₅溶液其抑菌率接近100%。表面活性剂,抑菌性和荧光性能赋予了OX-CQDs-C₁₂H₂₅的多种功能性。