Excellent alkene epoxidation catalytic activity of macrocyclic‐based complex of dioxo‐Mo(VI) on supermagnetic separable nanocatalyst

A phenoxybutane‐based Schiff base complex of cis‐dioxo‐Mo(VI) was supported on paramagnetic nanoparticles and characterized using powder X‐ray diffraction, infrared, diffuse reflectance and atomic absorption spectroscopies, scanning and transmission electron microscopies and vibrating sample magnetometry. The separable nanocatalyst was tested for the selective epoxidation of cyclohexene, cyclooctene, styrene, indene, α‐pinene, 1‐octene, 1‐heptene, 1‐dodecene and trans‐stilbene using tert‐butyl hydroperoxide (80% in di‐tert‐butyl peroxide–water, 3:2) as oxidant in chloroform. The catalyst was efficient for oxidation of cyclooctene with 100% selectivity for epoxidation with 98% conversion in 10 min. We were able to separate magnetically the nanocatalyst using an external magnetic field and used the catalyst at least six successive times without significant decrease in conversion. The turnover frequency of the catalyst was remarkable (2556 h^?1 for cyclooctene). The proposed nanomagnetic catalyst has advantages in terms of catalytic activity, selectivity, catalytic reaction time and reusability by easy separation.     

Cobalt(II) acetylacetonate complex immobilized on aminosilane‐modified SBA‐15 as an efficient catalyst for epoxidation of trans‐stilbene with molecular oxygen

From environmental and economic points of view, it is highly desirable to develop a clean and efficient catalytic process to produce epoxides. An attractive approach is to use a solid, recyclable catalyst and molecular oxygen as the oxidant without any sacrificial reductant or other additives. Nonetheless, the catalysts reported up to now still cannot balance catalytic activity with epoxide selectivity. It is of great importance to explore novel catalysts with both high activity and selectivity for the epoxidation of olefins. In this work, cobalt(II) acetylacetonate (Co(acac)₂) was covalently bonded to the silica surface of SBA‐15 molecular sieve by multi‐step grafting using 3‐aminopropytrimethoxysilane (APTS) as coupling agent. Characterizations with nitrogen physisorption, X‐ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis suggested that the metal complex was successfully immobilized on the aminosilane‐modified SBA‐15 surface and the channel structure remained intact. The synthesized Co(acac)₂APTS@SBA‐15 catalyst was used in the epoxidation of trans‐stilbene (TS) with molecular oxygen. Compared to the sample prepared by the impregnation method as well as Co(acac)₂ solutions under the same reaction conditions, the Co(acac)₂ immobilized catalyst exhibited remarkably higher TS conversion and trans‐stilbene oxide (TSO) selectivity. An increase in TS conversion with Co content was observed when the Co loading was lower than 0.70% and the 0.70Co(acac)₂APTS@SBA‐15 sample exhibited the best catalytic performance. Up to 50.1% of TS conversion could be achieved within 6 h, affording TSO selectivity as high as 96.7%. The superior catalytic performance of this particular catalyst is attributed to the high activity of the immobilized Co(acac)₂ species on SBA‐15. Copyright © 2016 John Wiley & Sons, Ltd.     

聚苯乙烯键合麻黄碱-Co(Ⅱ)络合物对烯烃环氧化反应的催化作用

聚苯乙烯键合麻黄碱 Ｃｏ（Ⅱ）络合物对烯烃环氧化反应的催化作用刘庆艳刘必前何纪纲（中国科学院化学研究所北京１０００８０）关键词环氧化，分子氧，烯烃，醛，高分子催化剂烯烃的环氧化反应是将烯烃进行氧化转化的重要反应［１］．由于高分子催化剂具有与反应...     

Cobalt imine–pyridine–carbonyl complex functionalized metal–organic frameworks as catalysts for alkene epoxidation

Aerobic epoxidation of alkene is a green and economical route to produce epoxides. For such reaction, transition metal complexes exhibit favorable catalytic activity. In this work, NH₂-MIL-101, a stable metal–organic framework (MOF) material with large surface area and high pore volume, was functionalized with pyridine-2,6-dicarbaldehyde and Co(NO₃)₂, to realize the immobilization of Co(II) via imine–pyridine–carbonyl (N,N,O) tridentate ligands bonding to MOF skeleton. The modified materials were applied as heterogeneous catalysts for the aerobic epoxidation of cyclohexene at ambient temperature, and multiple factors were studied to explore their influences on catalytic effects. Under the optimal reaction conditions, satisfactory substrate conversion and epoxide selectivity were reached. In addition, this catalytic system is suitable for a variety of alkene substrates. Furthermore, recycle experiments and infrared spectroscopy characterization illustrated that the coordination surroundings of Co are altering smoothly during the reaction process, thus having an impact on the performance of catalyst.

     

钴-席夫碱-壳聚糖/凹凸棒土对苯乙烯环氧化的催化性能

以NaOH固化法制备的壳聚糖/凹凸棒土（CS/ATP）复合树脂为载体,以水杨醛和天冬氨酸合成的席夫碱为配体,分别合成Co、Mn、Cu、Fe和Ni的席夫碱金属配合物及其负载型席夫碱金属配合物,并通过FT-IR对其进行结构表征,且以苯乙烯为底物,分子氧为氧源,分别考察了各种催化剂对苯乙烯的环氧化性能。 实验结果表明,在小分子席夫碱金属配体中,Co-Schiff碱催化性能较好。 将Co-Schiff碱负载到CS/ATP复合树脂中,综合考察了Co-Schiff碱-CS/ATP的用量、温度、时间对苯乙烯催化环氧化性能的影响,结果表明,反应温度为80 ℃,反应时间为8 h,苯乙烯的转化率达93.1%。     

Y型分子筛固载Co(Salprn)配合物的制备及催化烯烃环氧化性能

采用自由配体法将双水杨醛缩丙二胺席夫碱钴配合物Co(Salprn)封装于Y型分子筛超笼中,并通过X射线衍射、漫反射UV-Vis光谱、FT-IR光谱和差热分析技术对所制备的催化剂进行了表征。该催化剂样品( [Co(Salprn)]-Y)在苯乙烯环氧化反应中较纯配合物Co(Salprn)表现出很高的催化活性。反应条件（包括溶剂、催化剂用量、异丁醛浓度和反应时间）对催化性能有较大影响。研究结果还表明,[Co(Salprn)]-Y对其他烯烃的环氧化也具有较高催化活性。其活性顺序为苯乙烯﹥环己烯﹥环辛烯﹥正辛烯。     

Terbium–organic framework as heterogeneous Lewis acid catalyst for β‐aminoalcohol synthesis: Efficient,reusable and green catalytic method

A terbium–organic framework (Tb‐MOF) was prepared using a previously reported procedure. Tb‐MOF was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, powder X‐ray diffraction and surface area analysis. Tb‐MOF was employed as a heterogeneous Lewis acid catalyst for the synthesis of β‐aminoalcohols. Also, the effect of ultrasonic irradiation was examined in the catalytic aminolysis of styrene oxide. The reaction conditions were optimized by variation of reaction time, catalyst concentration and solvent. A variety of β‐aminoalcohols were synthesized and characterized. The Tb‐MOF catalyst showed excellent selectivity and high yield for these transformations.     

Olefin epoxidation with tert-butyl hydroperoxide catalyzed by functionalized polymer-supported copper(II) Schiff base complex

Abstract  

A new polymer-supported Cu(II) Schiff base complex has been synthesized and characterized by elemental (including metal) analysis, FT-IR spectroscopy, UV–Vis diffuse reflectance spectroscopy, thermogravimetric analysis, and scanning electron microscopy. The catalytic performance of this complex was evaluated in the epoxidation of styrene in acetonitrile/N,N-dimethylformamide (9:1) mixture with 70% tert-butyl hydroperoxide as an oxidizing agent under liquid phase reaction conditions for selective synthesis of styrene oxide. Suitable reaction conditions have been optimized by considering the effects of various reaction parameters such as temperature, reaction time, solvent, oxidant, catalyst amount, and styrene to hydroperoxide molar ratio for the maximum conversion of styrene as well as selectivity of styrene oxide. We have also investigated the epoxidation reaction of various olefins under the optimized reaction conditions. Comparison between catalytic activities of the polymer-supported Cu(II) Schiff base complex and its homogeneous analogue showed that the polymer-supported catalyst was more active. This heterogeneous complex was reused for five times. The selectivity of the heterogeneous catalyst does not change even after five times of reusing.     

Palladium nanoparticles immobilized on Schiff base‐functionalized mesoporous silica as a highly efficient and magnetically recoverable nanocatalyst for Heck coupling reaction

A new magnetically recoverable nanocatalyst was prepared by functionalization of mesoporous silica (SBA‐15) with a Schiff base ligand, and then immobilization of palladium nanoparticles on it using a simple procedure. This heterogeneous catalyst was fully characterized using appropriate analyses and its catalytic efficiency was investigated in Heck reaction using iodo‐, bromo‐ and chlorobenzene derivatives and styrene, with the aim of synthesizing stilbene derivatives, a class of compounds with a variety of pharmacological properties. Some of the characteristics of this nanocatalyst include good dispersion of palladium nanoparticles on the SBA‐15 support, easy separation, catalyses the production of stilbene derivatives in a short time with excellent yields even for bromo‐ and chlorobenzene, and preservation of its catalytic activity after eight reaction cycles.     

MCM-41固载Co席夫碱配合物的制备及其催化烯烃环氧化的研究

环氧化合物作为有机合成中间体具有广泛应用,催化烯烃环氧化一直是催化化学中的一个重要课题[1～2].尽管已经报道了以过酸、过氧化氢、烷基过氧化物、或分子氧为氧化剂,以金属配合物(通常为钌、钼、钛的配合物)为催化剂的反应体系,但对环氧化物的选择性却很低[3].另外,除了需探索具有高选择性的催化体系外,应用分子氧或空气作为氧化剂更适宜于经济和安全的要求.目前,在以分子氧作为氧化剂,均相催化烯烃环氧化的研究中,应用醛类化合物作为氧转移试剂是一种有效的和方便的促进烯烃环氧化的方法[4].但是,均相催化剂难于分离和重复使用,因此…     

Liquid-phase epoxidation of styrene with O2 over alkali metal salt impregnated CoAPO-5

Liquid-phase epoxidation of styrene with atmospheric O₂ was conducted over CoAPO-5 molecular sieves.The catalytic performance of CoAPO-5 can be significantly improved by alkali metal salt impregnated on it,and styrene conversion and selectivity to styrene oxide reached 85%and 69%respectively when CsCl was impregnated on it.The catalyst was recyclable and exhibited similar catalytic activity and selectivity even after three catalytic reaction cycles.     

Synthesis,characterization, density functional theory studies and antibacterial activity of a new Schiff base dioxomolybdenum(VI) complex with tryptophan as epoxidation catalyst

A cis ‐dioxomolybdenum(VI) complex was prepared with MoO₂(acac)₂ and a Schiff base ligand (2‐((2‐hydroxybenzylidene)amino)‐3‐(1H ‐indol‐3‐yl)propanoic acid) derived from salicylaldehyde and l ‐tryptophan in ethanol and designated as [MoO₂(Sal‐Tryp)(EtOH)]. It was characterized using several techniques including thermogravimetric and elemental analyses and mass, Fourier transform infrared and UV–visible spectroscopies. Theoretical calculations were performed using density functional theory for studying the molecular structure. An in vitro antibacterial activity evaluation showed that [MoO₂(Sal‐Tryp)EtOH] complex exhibits good inhibitory effects against Gram‐positive (Bacillus subtilis , Staphylococcus aureus ) and Gram‐negative (Escherichia coli , Pseudomonas aeruginosa ) bacteria in comparison to standard antibacterial drugs. It was also found that [MoO₂(Sal‐Tryp)EtOH] complex successfully catalyses the epoxidation of cyclooctene, norbornene, cyclohexene, styrene, α‐methylstyrene and trans ‐stilbene, with 45–100% conversions and 64–100% selectivities. Based on the obtained results, the heterogeneity and reusability of the catalyst seem promising.     

Amelioration of H4[W12SiO40] by nanomagnetic heterogenization: For the synthesis of 1H–pyrazolo[1,2‐b]phthalazinedione derivatives

We conveniently coated silicotungstic acid (STA, H₄[W₁₂SiO₄₀]) on amino‐functionalized Si–magnetite nanoparticles, as surface functionalization of magnetic nanoparticles is an excellent way for green and efficient catalysis. The nanoparticles were structurally characterized using various techniques. The catalytic activity and recyclability of the STA–amine–Si–magnetite nanoparticles were probed through synthesis of 1H–pyrazolo[1,2‐b]phthalazinedione derivatives. The reaction proceeds smoothly to provide products in excellent yields and short reaction times. The catalyst could be readily recovered using a simple external magnet and reused several times without any significant loss in activity. Herein, we report a comparison of the activity of H₄[W₁₂SiO₄₀] as a homogeneous and heterogeneous catalyst, the latter being found to be more efficient. The findings offer effective methods for environmentally friendly synthesis of pyrazolo[1,2‐b]phthalazinedione derivatives.     

Sodalite‐type Cu‐based Three‐dimensional Metal–Organic Framework for Efficient Oxygen Reduction Reaction

Inspired by copper‐based oxygen reduction biocatalysts, we have studied the electrocatalytic behavior of a Cu‐based MOF (Cu‐BTT) for oxygen reduction reaction (ORR) in alkaline medium. This catalyst reduces the oxygen at the onset (E_onset) and half‐wave potential (E^1/2) of 0. 940 V and 0.778 V, respectively. The high halfway potential supports the good activity of Cu‐BTT MOF. The high ORR catalytic activity can be interpreted by the presence of nitrogen‐rich ligand (tetrazole) and the generation of nascent copper(I) during the reaction. In addition to the excellent activity, Cu‐BTT MOF showed exceptional stability too, which was confirmed through chronoamperometry study, where current was unchanged up to 12 h. Further, the 4‐electrons transfer of ORR kinetics was confirmed by hydrodynamic voltammetry. The oxygen active center namely copper(I) generation during ORR has been understood by the reduction peak in cyclic voltammetry as well in the XPS analysis.     

Highly effective hydration of olefins using a wool‐palladium complex as a catalyst

The hydration of styrene, 2‐cyclohexen‐1‐one and 5‐hexen‐2‐one to α‐methylbenzyl alcohol, 3‐hydroxy‐cyclohexanone and 5‐hydroxy‐2‐hexanone was investigated using a wool‐supported palladium catalyst under mild conditions of temperature and pressure. The yields amounted to 82.0, 92.0 and 99.3% respectively and were greatly affected by the palladium content in the complex, the ratio of substrate/catalyst, the reaction temperature and the kind of solvent. The catalyst was very stable and could be re‐used several times without any remarkable change in the catalytic activity. Copyright © 2006 John Wiley & Sons, Ltd.     

Template‐Induced Diverse Metal–Organic Materials as Catalysts for the Tandem Acylation–Nazarov Cyclization

In our continuing quest to develop a metal–organic framework (MOF)‐catalyzed tandem pyrrole acylation–Nazarov cyclization reaction with α,β‐unsaturated carboxylic acids for the synthesis of cyclopentenone[b]pyrroles, which are key intermediates in the synthesis of natural product (±)‐roseophilin, a series of template‐induced Zn‐based ( 1–3 ) metal‐organic frameworks (MOFs) have been solvothermally synthesized and characterized. Structural conversions from non‐porous MOF 1 to porous MOF 2 , and back to non‐porous MOF 3 arising from the different concentrations of template guest have been observed. The anion–π interactions between the template guests and ligands could affect the configuration of ligands and further tailor the frameworks of 1–3 . Futhermore, MOFs 1–3 have shown to be effective heterogeneous catalysts for the tandem acylation–Nazarov cyclization reaction. In particular, the unique structural features of 2 , including accessible catalytic sites and suitable channel size and shape, endow 2 with all of the desired features for the MOF‐catalyzed tandem acylation–Nazarov cyclization reaction, including heterogeneous catalyst, high catalytic activity, robustness, and excellent selectivity. A plausible mechanism for the catalytic reaction has been proposed and the structure–reactivity relationship has been further clarified. Making use of 2 as a heterogeneous catalyst for the reaction could greatly increase the yield of total synthesis of (±)‐roseophilin.     

Covalent supporting of novel dioxo‐molybdenum tetradentate pyrrole‐imine complex on Fe3O4 as high‐efficiency nanocatalyst for selective epoxidation of olefins

A novel Mo(VI) tetradentate Schiff base complex based on two pyrrole‐imine donors was anchored covalently on Fe₃O₄ nanoparticles and characterized using physicochemical techniques. The catalytic epoxidation process was optimized in terms of the effects of solvent, reaction temperature, kind of oxidant and amount of oxidant and catalyst. Then the novel heterogeneous nanocatalyst was used for the efficient and selective catalytic epoxidation of internal alkenes (cyclohexene, cyclooctene, α‐pinene, indene and trans ‐1,2‐diphenylethene) and terminal alkenes (n ‐heptene, n ‐octene, n ‐dodecene and styrene) using tert ‐butyl hydroperoxide (70% in water) as oxidant in 1,2‐dichloroethane as solvent. The prepared nanocatalyst is very effective for the selective epoxidation of cis ‐cyclooctene with 100% conversion, 100% selectivity and turnover frequency of 1098 h⁻¹ in just 30 min. The magnetic nanocatalyst was easily recovered using an external magnetic field and was used subsequently at least six times without significant decrease in conversion.     

Ruthenium Complexation in an Aluminium Metal–Organic Framework and Its Application in Alcohol Oxidation Catalysis

A ruthenium trichloride complex has been loaded into an aluminium metal–organic framework (MOF), MOF‐253, by post‐synthetic modification to give MOF‐253‐Ru. MOF‐253 contains open bipyridine sites that are available to bind with the ruthenium complex. MOF‐253‐Ru was characterised by elemental analysis, N₂ sorption and X‐ray powder diffraction. This is the first time that a Ru complex has been coordinated to a MOF through post‐synthetic modification and used as a heterogeneous catalyst. MOF‐253‐Ru catalysed the oxidation of primary and secondary alcohols, including allylic alcohols, with PhI(OAc)₂ as the oxidant under very mild reaction conditions (ambient temperature to 40 °C). High conversions (up to >99 %) were achieved in short reaction times (1–3 h) by using low catalyst loadings (0.5 mol % Ru). In addition, high selectivities (>90 %) for aldehydes were obtained at room temperature. MOF‐253‐Ru can be recycled up to six times with only a moderate decrease in substrate conversion.     

Epoxidation of alkenes with molecular oxygen and isobutyraldehyde catalyzed by immobilized vitamin B12 within Al-MCM-41

Vit-B₁₂/ Al-MCM-41 catalyzed successfully the epoxidation either of cis or trans — stilbene with O₂ as oxidant and isobutyraldehyde as co-reductant with 86–98% reactivity and 97–100% selectivity. Other olefins such as norbornene and styrene undergo epoxidation reaction under similar conditions with good to fair selectivity. Details of the reactions will be presented in this article.     

Synthesis of Fe‐MCM‐41 from silatrane and FeCl3 via sol–gel process and its epoxidation acivity

An iron‐containing mesoporous molecular sieve, or Fe‐MCM‐41, was successfully synthesized the via sol–gel technique using silatrane and FeCl₃ as the silicon and iron sources, and was characterized using various techniques. Many factors were investigated, namely, reaction temperature and time, calcination rate, and iron amount in the reaction mixture. It was found that the optimum conditions in which to synthesize Fe‐MCM‐41 was to carry out the reaction at 60 °C for 7 h using a 1 °C min^?1 calcination rate and a 550 °C calcination temperature. The catalytic activity and selectivity of styrene epoxidation using hydrogen peroxide showed that the selectivity of the styrene oxide reached 65% at a styrene conversion of 22% over the 1%wt catalyst. Copyright © 2008 John Wiley & Sons, Ltd.