一种阴离子功能化的氮杂环卡宾-锂配合物的合成与结构

氮杂环卡宾(NHC)作为有机膦的替代物在金属有机化学中的应用受到了愈来愈广泛的关注,由于其毒性小、给电子能力强、空间和电子效应很易通过改变氮原子上取代基进行调控,将这类配体用于后过渡金属催化剂,可大大改善这些催化剂在各类均相催化反应中的反应活性及选择性[1].     

马卡斯电子转移反应理论及其在有机化学中的应用

近年来电子转移反应的研究,可以认为是有机化学领域中的前沿。它在有机化学和生命过程中均占有重要地位,而关于电子转移反应的马卡斯(Mar-cus)理论,提供了一个研究这些反应的定量物理     

Pd-N-杂环卡宾化合物催化的Heck反应、Suzuki反应进展

Pd催化的C—C键偶联反应是形成碳—碳单键的重要反应之一.传统上,使用膦化合物为配体来调整催化活性及选择性.但大多数Pd-膦化合物对空气稳定性差,容易被氧化;在溶液中易于解离出膦配体而降低催化剂稳定性,通常需要给反应体系中加入较多的膦配体以保持催化剂的稳定性和活性.1991年发现的稳定N-杂环卡宾(NHC)类配体具有富含电子、给电子能力强,对金属配位能力强,结构易修饰等特点,使得金属-NHC化合物成为金属有机化学、催化等领域研究新的焦点.Pd-NHC化合物已经可催化多类有机反应,是继传统Pd-膦催化剂外的又一类高效催化剂.综述了近年来不同结构的NHC如单齿简单NHC、双齿NHC、含其它配位原子的NHC等配体与Pd的配合物在Heck反应、Suzuki反应等偶联反应中的应用.     

分子碘催化的有机化学反应

从有机合成化学的角度,按反应类型综述了分子碘作为催化剂在有机化学中的应用,碘催化的反应主要涉及保护基团的形成和裂解、氧化和还原反应、成环反应、加成反应、取代反应和重排反应等。     

分子碘催化的有机化学反应

从有机合成化学的角度,按反应类型综述了分子碘作为催化剂在有机化学中的应用,碘催化的反应主要涉及保护基团的形成和裂解、氧化和还原反应、成环反应、加成反应、取代反应和重排反应等。     

什么是元素有机化学?

什么是元素有机化学？单自兴（武汉大学化学系４３００７２）元素有机化学是化学科学中发展最迅速的分支学科之一。元素有机化学的研究，提出一系列新概念、新结构、新理论，丰富和强化了化学科学的理论宝库；元素有机化学的研究，导致众多新试剂、新催化剂、新反应、新方...     

分子碘催化的有机化学反应

从有机合成化学的角度,按反应类型综述了分子碘作为催化剂在有机化学中的应用,碘催化的反应主要涉及保护基团的形成和裂解、氧化和还原反应、成环反应、加成反应、取代反应和重排反应等.     

有机金属化学

化学这门学科以往曾仔细加以分类,认为除了物理化学外,可分成无机化学和有机化学二大类,但是,最近二十年来,由于无机化学和有机化学的相结合,出现了第三类化学,即有机金属化学。它的飞速发展,已成为当前最活跃的化学领域之一。在有机化学教科书中详细介绍的Grignard试剂,是非常有用的反应试剂,而它本身就是烷基和镁相结合的有机金属化合物。Reformatsky反应中的反应试剂就是BrZnCH_2COOR这一有机锌化合物。具有齐聚结构的烷基锂既是阴离子聚合的催化剂,又是有机合成中有用的试剂。早已众所周知的以Sandmeyer,Gattermann,Ullmann,等人命名的反应一向看作是应用铜催化剂的反应,现在则可看作是有机铜化合物的反应。有机金属化学之所以迅速发展,是以二茂铁结构之阐明,及Ziegler-Natta催化剂之发     

四卤化碳: 强碱反应体系顺磁共振研究

单电子转移反应是物理有机化学中十分活跃的研究领域之一,现已发现许多有机反应中都存在着单电子转移过程。探讨不同的单电子转移反应体系,了解其中电子给、受体之间的相互作用,不仅对深入了解反应机理有理论     

非金属有机催化剂及其在有机化学反应中的应用

非金属有机催化剂在有机化学反应中有着独特的催化性能和优良的催化效果,尤其是在不对称合成中应用广泛.综述了近年来几类常用的非金属有机催化剂和它们所催化的各类有机化学反应包括不对称合成反应,同时对其催化机理做了总结.     

Interface Engineering in Two‐Dimensional Heterostructures: Towards an Advanced Catalyst for Ullmann Couplings

The design of advanced catalysts for organic reactions is of profound significance. During such processes, electrophilicity and nucleophilicity play vital roles in the activation of chemical bonds and ultimately speed up organic reactions. Herein, we demonstrate a new way to regulate the electro‐ and nucleophilicity of catalysts for organic transformations. Interface engineering in two‐dimensional heteronanostructures triggered electron transfer across the interface. The catalyst was thus rendered more electropositive, which led to superior performance in Ullmann reactions. In the presence of the engineered 2D Cu₂S/MoS₂ heteronanostructure, the coupling of iodobenzene and para‐chlorophenol gave the desired product in 92 % yield under mild conditions (100 °C). Furthermore, the catalyst exhibited excellent stability as well as high recyclability with a yield of 89 % after five cycles. We propose that interface engineering could be widely employed for the development of new catalysts for organic reactions.     

Pd nanoparticles supported on amphiphilic porous organic polymer as an efficient catalyst for aqueous hydrodechlorination and Suzuki-Miyaura coupling reactions

Developing efficient and recyclable heterogeneous catalysts for organic reactions in water is important for the sustainable development of chemical industry. In this work, Pd nanoparticles supported on DABCO-functionalized porous organic polymer was successfully prepared through an easy copolymerization and successive immobilization method. Characterization results indicated that the prepared catalyst featured big surface area, hierarchical porous structure, and excellent surface amphiphilicity. We demonstrated the use of this amphiphilic catalyst in two case reactions, i.e. the aqueous hydrodechlorination and Suzuki-Miyaura coupling reactions. Under mild reaction conditions, the catalyst showed high catalytic activities for the two reactions. In addition, the catalyst could be easily recovered and reused for several times. Also, no obvious Pd leaching and aggregation of Pd nanoparticles occurred up during the consecutive reactions.     

Immobilized Pd on a NHC functionalized metal–organic framework MIL-101(Cr): an efficient heterogeneous catalyst in Suzuki−Miyaura coupling reaction in water

A novel Pd−NHC functionalized metal–organic framework (MOF) based on MIL-101(Cr) was synthesized and used as an efficient heterogeneous catalyst in the C-C bond formation reactions. Using this heterogeneous Pd catalyst system, the Suzuki−Miyaura coupling reaction was accomplished well in water, and coupling products were obtained in good to excellent yields in short reaction time. The Pd−NHC−MIL-101(Cr) was characterized using some different techniques, including Fourier transform-infrared, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy, inductively coupled plasma and elemental analysis. The microscopic techniques showed the discrete octahedron structure of MIL-101(Cr), which is also stable after chemical modification process to prepare the catalyst system. The TEM images of the catalyst showed the existence of palladium nanoparticles immobilized in the structure of the catalyst, while no reducing agent was used. It seems that the NHC groups and imidazolium moieties in the structure of the MOF can reduce Pd (II) to Pd (0) species. This modified MOF substrate can also prevent aggregation of Pd nanoparticles, resulting in high stability of them in organic transformation. The Pd−NHC−MIL-101(Cr) catalyst system could be simply extracted from the reaction mixture, providing an efficient synthetic method for the synthesis of biaryls derivatives using the aforementioned coupling reaction. The Pd−NHC−MIL-101(Cr) catalyst could be recycled in this organic reaction with almost consistent catalytic efficiency.     

Reversibility of electrode reactions involving organic compounds

A general empirical approach allowing one to describe the kinetics and evaluate the mechanism of the electrode electron transfer reactions is offered. The approach is based on the electrode potentials, the vertical ionization potentials (oxidation), and the affinity to electron (reduction). An equation linking kinetic and thermodynamic parameters is derived. Electrode reactions involving organic compounds are discussed in polarographic terms. The conclusion is drawn that most electron transfer reactions involving organic compounds are reversible, and that the irreversibility of the net electrode reaction is due to the irreversibility of subsequent chemical and electrochemical stages. An experimental observation of the slow electron transfer is possible in the cases of a substantial reorganization of molecules in the presence of fast subsequent chemical and electrochemical reactions.     

Recent Developments on Catalytic Applications of Nano-Crystalline Magnesium Oxide

Nanocrystalline metal oxides, MgO, CuO, ZnO, TiO₂ as catalysts or catalyst supports have been received much attention in the recent years, especially nanocrystalline magnesium oxide (NAP-MgO) has been used as a recyclable catalyst for Wittig, Wadsworth–Emmons, aza-Michael, Baylis–Hillman, Strecker, Aldol, Claisen-Schmidt condensation and other useful organic reactions. In general, it is reported that nanocrystalline magnesium oxide shows better activity in many organic reactions. These high reactivities are due to high surface areas combined with unusually reactive morphologies. The nanomaterials were also explored as supports to make supported metal catalysts for the organic reactions. The higher activity of these catalysts was studied partly to understand the mechanism of the reaction, the putative reaction pathways were preliminarily presented with the help of spectroscopic support, XPS, silicon, and phosphorus NMR spectroscopy. The catalysts are recovered and reused for several cycles. These catalytic systems are expected to contribute to the development of benign chemical processes.     

Concentration Dependent Catalytic Activity of Glutathione Coated Silver Nanoparticles for the Reduction of 4-Nitrophenol and Organic Dyes

In the present study, we have synthesized glutathione modified silver nanoparticles (GSH-AgNPs) in aqueous medium and are characterized by absorption, high resolution transmission electron microscope (HR-TEM), selective area electron diffraction (SAED) pattern, dynamic light scattering (DLS), Zeta potential and Fourier transform infrared (FT-IR) spectroscopic measurements. Catalytic activity of GSH-AgNPs has been evaluated for the reduction reactions of 4-nitrophenol (4-NP), methylene blue (MB dye) and eosin Y (EY dye) in presence of sodium borohydride including the effect of catalyst concentration on the catalytic activity. Furthermore, the rate constants of reduction reactions are determined, which are linearly enhanced upon increasing the concentrations of GSH-AgNPs. It is explored that reduction reactions such as 4-NP, organic dyes by NaBH₄ in the presence of catalyst follow a pseudo first order kinetics. The catalytic reduction of 4-NP and organic dyes proceed with a faster rate even in the presence of nanomolar concentration of catalyst.     

Mechanistic study of alcohol oxidation by the Pd(OAc)(2)/O(2)/DMSO catalyst system and implications for the development of improved aerobic oxidation catalysts

The Pd(OAc)2/O2/DMSO catalyst system displays impressive versatility in the aerobic oxidation of organic substrates, ranging from alcohols to olefins. This report details mechanistic insights into these reactions. Dimethyl sulfoxide (DMSO) plays no redox role in the chemistry, and kinetic experiments identify the turnover-limiting step as DMSO-promoted oxidation of palladium(0) by molecular oxygen. The "chemical oxidase" pathway characterized for this catalyst system holds great promise for the design of new aerobic oxidation reactions.     

Efficient photochemical electron transfer sensitization of homogeneous organic reactions

Photochemical electron transfer induced reactions have become an interesting tool in organic synthesis since transformations can be easily performed which are difficult or impossible with more conventional organic reactions. In this context, electron transfer sensitized reactions are frequently used since the sensitizer can be considered as a catalyst. Various intermediates such as radical ions with a variety of reaction possibilities are involved. Nevertheless, the reactions have been performed with high yields and high selectivities. Particular attention is paid to the stability of the sensitizer. Reaction steps regenerating the sensitizer from different intermediates are discussed. In photochemical electron donor and acceptor sensitized transformations, these steps are often part of the main reaction course. In other cases, co-sensitizers or mediators significantly enhance the efficiency of the transformations although the number of reactive intermediates is increased.     

A highly enantioselective [4+2] cycloaddition involving aldehydes and β,γ-unsaturated-α-keto esters

A stereoselective inverse electron demand oxo-Diels-Alder reaction involving electron poor dienes (γ-aryl-β,γ-unsaturated-α-keto ester) and electron rich dienophiles has been studied. These cycloaddition reactions are extremely useful for the construction of O-, N-, S-centered heterocyclic compounds, which are routinely used in both synthetic organic and medicinal chemistry. The [4+2] hetero cycloaddition reactions involving various aldehydes and β,γ-unsaturated-α-keto esters were carried out in which three different types of substituted proline catalysts were examined. For these reactions, high selectivities (enantiomeric excess 93–98%) were obtained using catalyst 3. Due to the bulkiness of catalyst 3, compared to the other catalysts tested, it is more efficient at catalyzing these type reactions.     

Synthesis of nanomagnetic supported thiourea–copper(I) catalyst and its application in the synthesis of triazoles and benzamides

A novel nanomagnetic supported thiourea–copper(I) complex and inorganic–organic Takemoto‐like hybrid nanomagnetic catalyst was designed, and synthesized. The prepared naomagnetic catalyst was characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, energy‐dispersive X‐ray analysis, transmission and scanning electron microscopies, thermogravimetry, nitrogen adsorption/desorption, zeta potential and vibrating sample magnetometry. Furthermore, the fabricated dual‐role inorganic–organic hybrid catalyst shows a striking and robust catalytic activity for the synthesis of triazoles and benzamides through click and coupling reactions, respectively, under mild and eco‐friendly reaction conditions.