Synthesis of New Phase-Transfer Catalysts and Their Application in Asymmetric Alkylation

Despite phase transfer catalysis (PTC) is an important and useful method in organic synthesis, asymmetric synthesis using chiral phase-transfer catalyst has not been well documented and limited number of chiral phase-transfer catalyst have been developed^[1].In 1989,O'Donnell published his pioneering work in the asymmetric synthesis of α-amino acids by enantioselective alkylation of a prochiral protected glycine derivative using chiral phase-transfer catalyst^[2]. Since then, several groups reported their improvements on enantioselectivity and applicability on this useful synthetic reaction^[3,4]. However, almost all of the chiral phase-transfer catalysts reported so far are the derivatives of cinchona^[5]. In this presentation, we wish to describe the design and synthesis of a new type of chiral phase-transfer catalyst based on the camphor and its application in asymmetric alkylation of tert-bntyl glycinate-benzophenone Schiff base.     

A New Approach in Enantioselective Catalytic with Bis(oxazoline) Ligand-Metal Complexes

In recent years, the research of enantioselective-catalyzed reaction and the catalyst has got great development. Of the various chiral catalysts, great attention was given to the C₂-symmetry chiral bis(oxazoline)ligand-metal complexes for they could be easily synthesized and have shown good enantioselection in various catalytic processes, including cyclopropanation from dihalogenmethane^[1] and diazoacetate^[2].But no report has been found of enantioselective-catalyzed cyclopropanation from sulfonyl-carbanions and alkenes. The test of chiral cyclopropanation from sulfonylcarbanions with nickel bis(oxazolinyl)pyridine catalyst has been made in our lab, and alkylation of aldehydes with diethyl zinc in the presence of nickel or iron bis(oxazolinyl)pyridine was also tested (scheme 1). Some asymmetric effects were observed in these reactions.     

Self-assembled Alkylation of Atomically Flat Hydrogen-terminated Silicon (111) Surface By Using Highly Polarized Fluoroalkylsilane

Hydrogen-terminated silicon surface is of technological importance to semiconductor processes such as pre-gate^[1]. Re-contamination and re-oxidation on silicon surface become more stringent issues in order to meet the requirements in the process for producing reduced size IC chips. The modification of silicon surfaces by various strategies has attracted more attention in the past few years^[2-4]. The frequently used techniques to attach functional groups to silicon surfaces are via chemical^[2], photochemical^[3] and electrochemical reactions^[4]. Various ways to attach monlayers to silicon surfaces has been reported, including alkylation of silicon with alkenes, alkyenes, aldehydes, alcohols and Grigard reagents under photoactivated or catalytic reactions. Particularly, porous silicon prepared by chemical or electrochemical treatments has been extensively studied. Preparation of passivated layers on porous silicon surfaces has disadvantages that the silicon surfaces are damaged by reactive agents during the reaction or become porous for attachment of molecules. Recently, self-assembled monolayer of alcohols on porous silicon was reported at modest heating without the aid of catalyst or photoexcitation or potential^[5]. In the paper, we report a novel method to attach highly polarized fluoroalkylsilane on atomically flat Si(111) surface at room temperature and to form a self-assembled monolayer to prevent the silicon surface from re-contamination and re-oxidation.     

High Sensitivity Hyphenation System of Capillary Electrophoresis Combined Inductively Coupled Plasma Mass Spectrometer for Elemental Speciation Analysis

The proper functioning of life is critically dependent on trace elements in a number of different ways. Some trace elements are highly toxic whereas others, considered essential, are needed for the accomplishment of life process. A surge of evidence during the past 20 years has been leading to the conclusion that it is not the total element content but that of a particular species that should be determined if valid information on the essentiality or toxicity of a given element is to be obtained^[1-5]. Thus, speciation analysis has become one of the fastest developing areas of analytical chemistry towards the close of the 20^th century^[5]. The advantages of Capillary Electrophoresis include rapid analysis, low sample requirements, high separation efficiency and low operation costs^[6]. The separation potential of CE,with superior detection capability of ICPMS make CE-ICPMS a powerful tool for metal speciation.     

Synthesis of New Bis(oxazoline) Ligand-Metal Complexes

Great success has been achieved in the enantioselective-catalyzed reactions over the past few years. In the various catalyst, C₂-symmetric chiral bis(oxazoline)ligand-metal complexes accepted great attention in recent years for they showed effective enantioselection in various catalytic reactions and were easy to be prepared from available optically active amine acid^[1]. For the test of enantioselective-catalyzed cyclopropanation from sulfonyl-carbanions and alkenes, a series of new bis(oxazolinyl)pyridine complexes were synthesized. Nickel and iron was found as effective catalysts in the cyclopropanation from sulfonylcarbanions in previous research^[2]. Some nickel or iron bis(oxazolinyl)pyridines were prepared(scheme 1). These complexes were characterized with MS, IR and so on.     

CO Oxidation Activity and Characterization of Ag-Mn、Ag-Ce and Ag-Cu Mixed Oxide Catalysts

Catalytic oxidation is an efficient way to convert CO to CO₂ at low temperature. Precious metal catalysts such as Ft and Pd have been demonstrated to be very effective^[1]. However, attention has also been given to base metals due to the limited availability of precious metals. As a single component base metal catalyst cannot rival a precious metal catalyst, improvement in its activity has been attempted by combining several elements^[2,3]. In the present work, we studied redox and structure of Ag-M(M=Mn、Ce and Cu) catalysts to gain some evidence of the synergism between Ag and base metals, and investigated their catalytic activities.     

Low Temperature Oxidative Dehydrogenation of Ethane to Ethylene and Effect of Support over NiO/γ-Al2O3 Catalysts

Some excellent catalysts for ODE reaction,such as K-Sr-Bi-O-Cl^[1], LiCl/sulfated-zirconia^[2], which have high conversion of ethane and selectivity to ethylene, have been reported recently. But the relatively high reaction temperatures up to 620℃ and/or very low GHSV have been used over above catalyst systems. So the research aimed at searching for new catalysts with good performances at low temperatures appears to be desirable.     

Synthesis of Silica Hollow Spheres with Diameter Around 50 nm by Anionic Surfactant

Silica hollow spheres(SHSs) have attracted great attention because of their low toxicity,low density,large surface area,high chemical and thermal stability,and surface permeability.They can be widely applied in storage[1],catalysis[2],drug delivery[3,4],low-dielectric-constant materials[5],low-refractive materials[6-8],and so on.Up to now,there have been various methods to produce SHSs.Inorganic[9] or organic particles[10],such as polystyrene or calcium carbonate,were used as hard templates to create hollow cavities.However,the multistep synthetic process and the lack of structural robustness of the shells upon template removal process weaken their application.Soft templates,including oil-in-water emulsions[1],[2],vesicles[13],micelle[14,15] and gas bubbles[16],are applied widely.     

An Asymmetric Synthesis of Isoindolinones

Recently, the results from this laboratory showed that the reductive alkylation of protected (S)-malimide could be achieved in a high regio- and diastereoselective manner. The substituted 2-pyrrolidinones thus formed are versatile chiral building blocks which can be used in the asymmetric synthesis of pyrrolidines^[1,2],2-pyrrolidinones^[3,4] and β-hydroxy-γ-amino acids^[5,6]. As an extension of this work, and in combination with the current interest in the synthesis of isoindolin-1-ones, a study on the asymmetric reductive alkylation of phthalimide derived from (R)-phenylglycinol was undertaken.     

A New Mechanism for the Formation of the Ozone Hole in the Earth Atmosphere

It is generally accepted that the Earth ozone layer is depleted by chlorine atoms produced via solar photolysis of chlorofluorocarbons (CFCs) in the upper stratosphere^[1]. This photodissociation model predicts an ozone depletion maximum at an altitude between 30 and 40 km and negligible ozone depletion below 20 km^[1]. However, the Antarctic/Arctic ozone hole appearing in each spring is observed to be located at an altitude of about 15 km^[2]. The formation of the ozone hole has been attributed to heterogeneous reactions on the surface of polar stratosphere clouds (PSCs) consisting mainly of condensed water ice:HCl+ClONO₂→Cl₂+HNO₃^[3,4]. Recently, it has been observed that dissociation of CFCs by capture of low-energy electrons is enhanced by several orders of magnitude when CFCs are adsorbed on the surfaces of ice films of polar molecules such as H₂O and NH₃^[5,6]. This enhancement is due to transfer of electrons in precursors of solvated states in polar molecular ice to CFCs that then dissociate^[7]. This effect should be most efficient in the lower stratosphere of about 15 km, where low-energy electrons can be produced by cosmic-ray ionization and localized in precursors of solvated electrons in PSCs^[8]. Strong and straightforward evidence of this new mechanism for ozone depletion has also been found in data obtained from field measurements (satellites, balloons, etc.)^[8]. In this talk, we will present the data from both field and laboratory measurements and discuss the new mechanism for the formation of the ozone hole.     

Enantioselective Hydrogenation of Acetophenone over Cinchonidine-Stabilized and Supported Rhodium Clusters

Because of the importance of the chirality in chemicals in everyday, the synthesis of enantiomerically pure chiral compounds has become an important academic and commercial advantage. In asymmetric synthesis field, enantioselective catalysis has been the most challenging subject over the past decades. Among the numerous enantioselective heterogeneous catalysts, the rhodium is always an unsuccessful example under favorable reaction conditions with only 20%-30% enantiomeric excess (e.e.)^[1].And almost all of papers about heterogeneous enantioselective catalysis have reported that rhodium is not suitable for heterogeneous enantioselective hydrogenation^[1-3].     

Synthesis of Mesoporous Molecular Sieves via a Novel Templating Scheme

Since Mobil researchers reported the discovery of a new family of silica-based mesoporous molecular sieves (M41S) materials in 1992^[1,2], there has been a growing interest in using these materials as heterogeneous catalysts, catalyst supports, and nanocomposite host materials for novel applications. All these applications have stimulated many researchers to synthesize mesoporous materials via different templating schemes or synthesis pathways. So far, ionic and neutral surfactant including neutral alkylamine^[3], polyethlene oxide^[4], genimi^[5], and amphiphilic triblock copolymer^[6] have been the most commonly used as templates for the directing the formation of mesoporous.     

修饰NADH模拟物的金属-有机三元环光催化制氢

将含有不同还原型烟酰烟腺嘌呤二核苷酸(NADH)活性中心模拟物的有机配体H2L1和H2L2与钴离子配位自组装获得2例具有氧化还原活性且带有正电荷的金属-有机大环Co-L1和Co-L2.选择阴离子型钌基光敏剂[Ru(dcbpy)3]4-(dcbpy=2,2'-联吡啶-4,4'-二羧酸)作为光敏中心,金属-有机大环结构作为...     

锰催化苄基C—H键氟化反应机理的理论研究

采用密度泛函理论(Density Functional Theory,DFT),对锰催化剂Mn^III(salene)F作用下苄基C—H键氟化反应的机理进行了深入的理论研究。对该反应中涉及到的重要中间体和过渡态的能量、Mulliken电荷分布、前线分子轨道等进行了分析。计算结果表明采用[Mn^IV(OH)(salene)F]和[Mn^IV(salene)F₂]为催化剂催化苄基C—H键氟化反应所需的能垒分别为11.5 kcal·mol^-1和7.6 kcal·mol^-1。可见采用双氟催化剂[Mn^IV(salene)F₂],氟化反应的能垒较低,更有利于苄基C—H键的氟化。通过轨道分析,给出了反应过程中详细的电子转移情况,从本质上分析了苄基氟化反应的机理。研究表明中心金属上的氧原子可以获得和失去电子,在C—H活化过程中起到传递电子的作用。在电子转移过程中,Mn原子是最终的电子接受体。以上结果很好地解释了实验现象,为进一步研究金属催化C—H键氟化反应提供理论支持。     

Study on Sulphided WNi/USY+Al2O3 Catalyst by XPS

Ni-promoted tungsten catalysts are widely used for hydrotreating various petroleum fractions. The catalysts have to be sulphided prior to use in industry, because sulphided catalyst has higher activity and more stability. The influence of the sulphiding conditions on the performance of WNi/Al₂O₃ has been investigated by some reseachers^[1] except for WNi/USY+Al₂O₃ hydrocracking catalyst. In this paper, the optimal sulphiding conditions of WNi/USY+Al₂O₃ have been studied by XPS.     

Palladium-Catalyzed Carbonylative Reaction of Iodine Heterocyclic Compound with Alcohol

In the past few decades, much attention has been focused on palladium-catalyzed carbonylative reactions^[1,2], which is a simple method to synthesize some complicated compounds^[3,4]. This kind of reactions, however, can be carried out only when the substrates are arylhalide, heteroaryl halide, alkene halide,aryltrifluoromethyl-sulfonate and hypervalent iodonium salt^[5] etc. Herein, we report a palladium-catalyzed carbonylative reaction between 3,7-bis(N,N-dimethylamino)-10H-dibenz[b,e] iodinium iodide(1)^[6] with alcohols (2) at ambient temperature as shown in scheme.     

Effect of SO2 on the NO Oxidation over NiO/γAl2O3 Catalyst

NO is the dominant component of NO_x. It can be easily oxidized to NO₂ over active catalysts in the oxidizing exhaust gases. And then, the high reactive NO₂ can be removed completely further through adsorption or absorption approach. However, SO₂,another main contaminant in the exhaust, is well known to poison the oxidative catalysts. A strong deactivation for metal oxides supported on Al₂O₃ was found when catalysts had been exposed to the gas containing 500ppm SO₂. It was also reported that the inhibition effect of SO₂ was enhanced at low temperatures. But recently, some studies declare that the oxidation of propane can be promoted over Pt/γ-Al₂O₃ if a small amount of SO₂ (20 ppm) is present in the feed gas^[1]. Jang et al. have also found that SO₂ has a promoting effect for the oxidation of NO to NO₂ over CO₃O₄/γ-Al₂O₃ catalyst^[2]. These observations are meaningful because the existence of SO₂ in the oxidizing exhaust is often inevitable and the problem of catalyst deactivation by SO₂ has puzzled researchers for a long time.     

ATR-FTIR Study of Si(110) Surface Hydrogenated in NH4F-Based Mixtures

RCA (Radio Corporation of America) cleaning has been the important and critical step in semiconductor manufacturing for more than 30 years^[1]. As the electronics devices are shrinking and gate oxide is getting thinner, stringent requirements on metallic impurities,organic contamination and surface roughness on silicon wafer after wet chemical cleaning have attracted more attention in the mechanism of wet etching processes on Si(111) and Si(100) surfaces^[2=11]. In the past few years wet chemical and electrochemical etching of Si(110) in NH₄F solutions has been studied by using scanning tunneling microscopy (STM)^[12] and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR)^[13-14]. In the present work, we extend our study to Si(110) surface in NH₄F/HCl mixtures by using polarized attenuated total reflection FTIR (ATR-FTIR). We have compared the ex-situ ATR-FTIR results on Si(110) in various NH₄F/HCl solutions using Ge prism. Effects of potential on hydrogen-terminated structures on Si(110) surfaces have been investigated by employing in-situ electrochemical ATR-FTIR with double side polished single crystal silicon as a prism. Our ATR-FTIR spectra are correlated with the results obtained with in-situ STM.     

Catalytic Reduction of Nitric Oxide on SiO2/AlO3-supported Transition Metal Catalysts

Selective reduction of nitric oxide in pressence of oxygen is one of the major challenges in the automobile exhaust after-treatment for lean-bum gasoline engines and diesel engines. Besides Cu-ZSM-5, Pt and Pd based noble metal catalysts, alumina-supported silver catalysts show high activities on NOx conversion to nitrogen^[1,2]. However, NO conversion activities over silver on binary oxides have rarely been studied in detail^[3], although copper on SiO₂-Al₂O₃ catalyst was reported to have a high activity^[4] Here, NOx reduction activities on SiO₂-Al₂O₃-supported transition metal catalysts prepared by sol-gel method was investigated.     

XPS Spectra of K-Ru/MWNTs Catalysts for Ammonia Synthesis

Alkali metal and alkali oxide-promoted ruthenium has been found to be one of the most active catalysts for ammonia synthesis under atmospheric pressure^[1]. Recently, We found^[2] that the K-Ru/MWNTs catalyst showed very high activity for ammonia synthesis. It is suggested that the high activity is due to the special electronic and structural properties of the carbon nanotubes. Alkali and alkali oxide doped MWNTs have been reported to be more favorable for electronic transfer and hydrogen storage^[3]. In the ammonia synthesis,these properties may play important roles. In this study, K-Ru/MWNTs and Ru/MWNTs were prepared and characterized by XPS. We found that alkali oxide can improve the Ru dispersion similar to the classic catalysts for ammonia synthesis.