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排序方式: 共有890条查询结果,搜索用时 31 毫秒
1.
Dr. Cédric Colomban Anthonio H. Tobing Gourab Mukherjee Dr. Chivukula V. Sastri Dr. Alexander B. Sorokin Dr. Sam P. de Visser 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(63):14320-14331
The biodegradation of compounds with C−F bonds is challenging due to the fact that these bonds are stronger than the C−H bond in methane. In this work, results on the unprecedented reactivity of a biomimetic model complex that contains an N-bridged diiron-phthalocyanine are presented; this model complex is shown to react with perfluorinated arenes under addition of H2O2 effectively. To get mechanistic insight into this unusual reactivity, detailed density functional theory calculations on the mechanism of C6F6 activation by an iron(IV)-oxo active species of the N-bridged diiron phthalocyanine system were performed. Our studies show that the reaction proceeds through a rate-determining electrophilic C−O addition reaction followed by a 1,2-fluoride shift to give the ketone product, which can further rearrange to the phenol. A thermochemical analysis shows that the weakest C−F bond is the aliphatic C−F bond in the ketone intermediate. The oxidative defluorination of perfluoroaromatics is demonstrated to proceed through a completely different mechanism compared to that of aromatic C−H hydroxylation by iron(IV)-oxo intermediates such as cytochrome P450 Compound I. 相似文献
2.
In this study, a new polymeric functionalized magnetic nanocatalyst containing a molybdenum Schiff base complex was prepared using a few consecutive steps. Poly (methylacrylate)-coated magnetic nanoparticles were synthesized via radical polymerization of methyl acrylate onto modified magnetic nanoparticles followed by the amidation of the methyl ester groups with hydrazine. Polymeric functionalization efficiently provides the advantage that more catalytic units can be grafted on the surface of magnetic nanoparticles. The functionalization process was continued with salicylaldehyde which introduced Schiff base groups on to the surface of the polymeric support. In the final step, the desired catalytic system was prepared via complexation of the Schiff base groups with MoO2(acac)2. The resulting nanoparticles were characterized by infrared spectroscopy, powder X-ray diffraction, scanning and transmission electron microscopy, elemental analysis, inductively coupled plasma optical emission spectrometry, vibrating sample magnetometry and thermogravimetric analysis. This heterogenized catalytic system was also found to be highly active, sustainable and recyclable nanocatalyst in alkene epoxidation. Eventually, the attractive features of the synthesized catalyst such as simple work-up, good stability, magnetic separation, high TOF and high surface area; make it appropriate for oxidation reactions. 相似文献
3.
由于巨大的潜在市场,乙烯的电化学氧化受到愈来愈多的关注。目前,主流的电化学氧化法仍以依赖于氧化还原媒介的介导氧化法为主,而这些媒介的使用在电解过程中产生大量的腐蚀性中间体,使其实际应用受到阻碍。直接电氧化法可有效规避此问题,但又受到低活性和低选择性的限制。在本工作中,我们针对目前最先进的钯催化直接氧化体系,在中性条件下开展了一系列电化学研究,以对该过程的机理获取更深入的认识。在氮气和乙烯氛围下,钯电极的循环伏安谱图有显著区别。我们发现电解过程中生成的Pd(Ⅱ)物种在乙烯氛围下可绕过原本的电化学还原路径,通过一个化学步还原为Pd(0),因此可能是乙烯氧化的活性位点。Pd(Ⅱ)物种所对应的还原峰也因此可作为乙烯吸附的数量的指标。通过电化学脉冲序列的设计,我们在钯催化剂上识别了两种具有不同吸附强度的乙烯,其强、弱吸附模式所对应的电荷转移比例约为0.3:1。弱吸附的乙烯在钯电极表面表现出可逆的吸脱附行为,而具有强吸附模式的乙烯无法通过物理过程脱附,可能指向到乙烯深度氧化过程。这项工作为进一步设计高性能乙烯直接电氧化催化剂提供了设计思路和方向。 相似文献
4.
Bize Gao Dr. Quanren Zhu Prof. Dr. Yanhui Yi Yue Li Guoxing Wu Yitong Guo Prof. Dr. Zhaochi Feng Prof. Dr. Hongchen Guo 《欧洲无机化学杂志》2023,26(22):e202200661
The epoxidation of propylene with dilute H2O2 aqueous solution over titanium silicalite-1 (TS-1) zeolite catalyst is a green chemical reaction for propylene oxide (PO) production. Carrying out the reaction in gas-phase can get rid of problems caused by using methanol solvent. This paper reports an attempt of using non-zeolite catalyst for the gas-phase epoxidation. Amorphous Ti/SiO2, obtained by grafting amorphous SiO2 with TCl4 in ethanol solvent in a chemical liquid-phase deposition (CLD) process, has been used as the catalyst. Results show that the CLD Ti/SiO2 with appropriate Si/Ti molar ratio is an active catalyst for gas-phase epoxidation, achieving 9.8 % propylene conversion and 66.9 % PO selectivity with 40.3 % H2O2 utilization, which indicates that this amorphous Ti/SiO2 catalyst deserves extensive studies in the future. 相似文献
5.
Dr. Peng Dong Tingna Shao Jinlian Li Xiaohui Zhang Prof. Yu Zhao Prof. Xinhong Zhao Prof. Guixian Li 《欧洲无机化学杂志》2023,26(33):e202300483
Cyclohexane epoxide, which contains highly active epoxy groups, plays a crucial role as an intermediate in the preparation of fine chemicals. However, controlling the epoxidation pathway of cyclohexene is challenging due to issues such as the allylic oxidation of cyclohexene and the ring opening of cyclohexane epoxide during the cyclohexene epoxidation process to form cyclohexane oxide. This review focuses on the structure-activity relationships and synthesis processes of various heterogeneous transition metal-based catalysts used in cyclohexene epoxidation reactions, including molybdenum(Mo)-based, tungsten(W)-based, vanadium(V)-based, titanium(Ti)-based, cobalt(Co)-based, and other catalysts. Initially, the mechanism of cyclohexene epoxidation by transition metal-based catalysts is examined from the perspective of catalytic active centers. Subsequently, the current research of cyclohexene epoxidation catalysts is summarized based on the perspective of catalyst support. Additionally, the differences between alkyl hydroperoxide, hydrogen peroxide (H2O2), and oxygen (O2) as oxidants are analyzed. Finally, the main factors influencing catalytic performance are summarized, and reasonable suggestions for catalyst design are proposed. This work provides scientific support for the advancement of the olefin epoxidation industry. 相似文献
6.
A Unified Strategy to 6–5–6–5–6‐Membered Epipolythiodiketopiperazines: Studies towards the Total Synthesis of Scabrosin Diacetate and Haematocin 下载免费PDF全文
Hannes F. Zipfel Prof. Dr. Erick M. Carreira 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(35):12475-12480
The family of epipolythiodiketopiperazine (ETP) natural products consists of over 200 members possessing a wide diversity of structures and biological activity. Recently, the subgroup of 6–5–6–5–6‐membered ETPs has gained substantial attention, which has resulted in several total syntheses. Despite all the efforts that have been invested into accessing these complex structures, no synthesis of scabrosin diacetate ( 1 a ) and its related esters has been reported. Herein, our attempts towards scabrosin diacetate ( 1 a ) and haematocin ( 3 ) starting from diketopiperazine 12 a as a late‐stage intermediate are presented. Diketopiperazine 12 a can be conveniently accessed in multigram quantities from aldehyde 18 and diketopiperazine 21 and was envisioned to serve as a general platform for the synthesis of 6–5–6–5–6‐membered ETPs. 相似文献
7.
The first montmorillonite‐supported surface single‐structure titanium complex: synthesis,characterization and catalytic activity in alkene epoxidation 下载免费PDF全文
Wei Xu Bo Yu Huaming Sun Jindou Yang Ying Zhang Zhenhua Wang Xi Chen Guofang Zhang Ziwei Gao 《Surface and interface analysis : SIA》2015,47(3):308-314
A well‐defined single‐site titanium‐modified montmorillonite (MMT) with only one geometric construction ((?SiO)3–Ti–NMe2) was obtained in moderate conditions. Reaction of tetrakis(dimethylamido)titanium with hydroxylated MMT was conducted by surface organometallic chemistry technique, and the surface structure was characterized by in situ Fourier transform infrared spectroscopy, 13C cross polarization magic angle spinning nuclear magnetic resonance, X‐ray photoelectron spectroscopy, extended X‐ray absorption fine structure, and elemental analysis. The catalytic activity in alkene epoxidation was evaluated, and the results revealed that the steric hindrance of the substances is responsible for the catalytic activity of the MMT‐supported titanium complex but to the characteristic restricted layer‐like structure of the MMT. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
8.
综述了以过氧化氢为氧源,多金属氧酸盐催化烯烃环氧化的研究进展,尤其是针对基于多金属氧酸盐的反应控制相转移催化体系近年来的研究进展进行了详细阐述. 相似文献
9.
Click functionalization of magnetite nanoparticles: A new magnetically recoverable catalyst for the selective epoxidation of olefins 下载免费PDF全文
A new magnetically recoverable heterogeneous molybdenum catalyst was developed by means of a click chemistry approach. First, silica‐coated magnetite nanoparticles were functionalized using a bidentate ligand via thiol–ene click reaction of mercaptopropyl‐modified magnetite nanoparticles with acrylic acid. Then, a molybdenum complex was covalently supported on the surface of the clicked silica‐coated magnetite nanoparticles. The prepared catalyst was characterized using Fourier transform infrared and inductively coupled plasma optical emission spectroscopies, X‐ray diffraction, vibrating sample magnetometry and transmission electron microscopy. The catalytic performance of the prepared heterogeneous catalyst was investigated in the epoxidation of olefins with tert‐butyl hydroperoxide as oxidant. This catalyst could be reused for five runs without significant loss of activity and selectivity. 相似文献
10.