Ligand-stabilized metal nanoparticles in organic solvent

This critical review reports the fundamental behavior of metal nanoparticles in different organic solvents, i.e., metal organosol. An overview on metal organosol and then their smart synthetic approaches, characterization, and potential applications in the fields of catalysis and spectroscopy with special emphasis on SERS are embodied. Aspects of organosol fabrication, stabilization, morphology control, growth mechanisms, and physical properties as mono- and bimetallic nanoparticles are discussed. The article inspires the repetitive usage of metal nanoparticles as stable deliverable organic and molecular compounds.     

各向异性金纳米粒子的制备及其在催化中的应用

尽管有关金纳米粒子催化的研究工作很多,但其中大多数都是采用传统的浸渍法将金盐负载到载体上、共沉淀或沉积-沉淀法制得负载的纳米粒子,但这些方法并未吸收最新的纳米技术。最近,金催化剂的研究者开发了在胶态悬浮液中制取金属纳米粒子,然后进行固载,从而使得单金属和双金属催化剂的催化活性和形貌控制取得较大进展。另一方面,最近十年出现了金纳米粒子合成的高级控制技术,得到了许多各向异性的金纳米粒子,且很容易制得新的形貌,可以控制纳米粒子的表面原子配位数和光学特性(可调的等离子体带),这些都与催化密切相关。这些形貌包括纳米棒、纳米星、纳米花、树枝状纳米结构或多面体纳米粒子等。除了高度关注各向异性金纳米粒子的最新开发的制备方法和性质,本综述也清楚地总结了这些纳米粒子独特的催化性能,以及通过提供更高催化性能的金催化剂、控制暴露的活性位,以及热、电和光催化的鲁棒性和可调性,从而给多相催化领域带来令人惊奇的潜在变革。     

A general synthetic strategy for oxide-supported metal nanoparticle catalysts

Despite recent exciting progress in catalysis by supported gold nanoparticles, there remains the formidable challenge of preparing supported gold catalysts that collectively incorporate precise control over factors such as size and size-distribution of the gold nanoparticles, homogeneous dispersion of the particles on the support, and the ability to utilize a wide range of supports that profoundly affect catalytic performance. Here, we describe a synthetic methodology that achieves these goals. In this strategy, weak interface interactions evenly deposit presynthesized organic-capped metal nanoparticles on oxide supports. The homogeneous dispersion of nanoparticles on oxides is then locked in place, without aggregation, through careful calcination. The approach takes advantage of recent advances in the synthesis of metal and oxide nanomaterials and helps to bring together these two classes of materials for catalysis applications. An important feature is that the strategy allows metal nanoparticles to be well dispersed on a variety of oxides with few restrictions on their physical and chemical properties. Following this synthetic procedure, we have successfully developed efficient gold catalysts for green chemistry processes, such as the production of ethyl acetate from the selective oxidation of ethanol by oxygen at 100 degrees C.     

Selective oxidation using gold

This critical review covers the recent development of the catalytic properties of gold in the selective oxidation of organic compounds, highlighting the exciting contribution to the art of catalysis. The unique, outstanding properties of nanometre-scale particles of gold, a biocompatible non-toxic metal, have allowed the development of a new generation of stable and selective catalysts for the conversion of many organic feedstocks to valuable chemicals. A critical discussion of the results of different research groups is presented along with attempts to correlate the catalytic properties with catalyst morphology in non-equivalent series of experiments.Particular emphasis has been given to the international efforts towards optimised synthesis of products of industrial appeal such as propylene oxide, vinyl acetate monomer, cyclohexanol/cyclohexanone, gluconic acid and glyceric acid (168 references).     

Catalytically active gold on ordered titania supports

Almost two decades have passed since supported Au nanoparticles were found to be active for CO oxidation. This discovery inspired extensive research addressing the origin of the unique properties of supported Au nanoparticles, the design and synthesis of potentially technical Au catalysts, and the extension of Au catalysis to other reactions. This tutorial review summarises the current understanding of the origin of the unique properties of titania-supported Au catalysts for carbon monoxide oxidation. The key issues of catalysis by nanostructured Au, effects of oxide support and active site/structure, especially those provided from model studies are discussed in detail. The successful synthesis of a highly catalytically active gold bilayer may lead to the design and synthesis of practically active Au nanofilm catalysts.     

Catalysis by gold dispersed on supports: the importance of cationic gold

There are many examples of catalysis in solution by cationic complexes of gold, and recent results, reviewed here in this critical review, demonstrate that cationic gold species on oxide and zeolite supports are also catalytically active, for reactions including ethylene hydrogenation and CO oxidation. The catalytically active gold species on supports are evidently not restricted to isolated mononuclear gold complexes, but include gold clusters, which for at least some reactions are more active than the mononuclear complexes and for some reactions less active. Fundamental questions remain about the nature of cationic gold in supported catalysts, such as the nature of the cationic gold clusters and the nature of gold atoms at metal-support interfaces (88 references).     

Development of heterogeneous olympic medal metal nanoparticle catalysts for environmentally benign molecular transformations based on the surface properties of hydrotalcite

In this review, we describe the development by our research group of highly functionalized heterogeneous Olympic medal metal (gold, silver, and copper) nanoparticle catalysts using hydrotalcite as a support, aimed towards Green and Sustainable Chemistry. Olympic medal metal nanoparticles can cooperate with the basic sites on the hydrotalcite surface, providing unique and high performance catalysis in environmentally-benign organic transformations such as aerobic oxidation of alcohols, lactonization of diols and selective deoxygenation of epoxides and nitro aromatic compounds.     

Strained small rings in gold-catalyzed rapid chemical transformations

Gold-catalyzed reactions, which have been widely explored over the past several years, are powerful tools in organic synthesis to access complex molecular frameworks, and some corresponding excellent reviews have been reported. However, little attention has been paid to summarize the reactions of strained small-ring-containing molecules catalyzed by gold. This critical review mainly puts its emphasis on the recent progress in the field of gold-catalyzed transformations of cyclopropyl-, cyclopropenyl-, epoxy- and aziridinyl-containing molecules. The rapid construction of interesting building blocks in organic synthesis from strained small rings catalyzed by gold has been summarized in this review (106 references).     

Facile functionalization of gold nanoparticles via microwave-assisted 1,3 dipolar cycloaddition

This contribution describes a simple and facile method for the functionalization of thiol-coated gold nanoparticles using microwave-assisted 1,3 dipolar cycloadditions. The developed procedure allows for the attachment of terminal alkynes onto azide-containing gold nanoparticles in nearly quantitative conversions within minutes. The utility of the method has been demonstrated by attaching a library of substituted alkynes onto gold nanoparticles in nearly quantitative yields. In a proof of principle study, we demonstrate the potential use of this methodology in catalysis by attaching palladium catalysts to the azide-containing gold nanoparticles and investigate the resulting materials as supported catalysts in Suzuki couplings. Activities that rival the nonsupported analogues were observed, demonstrating that the nanoparticle support does not interfere with the catalytic activity.     

Metal Nanoparticles Syntheses on Ionic Liquids Functionalized Mesoporous Silica SBA‐15

Supported metal nanoparticles hold great promise in heterogeneous catalysis as active and reusable catalysts for various organic transformations. Preparation methods of metal nanoparticles with excellent control over size, shape, and morphology on supports has significantly advanced to improve the performances of the resulting catalysts. Here, we aim to discuss the development of supported metal nanoparticles on mesoporous silica SBA‐15 in the presence of immobilized ionic liquids mostly based on examples from the previously reported results. This review highlights the preparation methods for size‐controlled syntheses and the immobilization of metal nanoparticles on solid supports, especially SBA‐15 by various techniques.     

Water‐ and Organo‐Dispersible Gold Nanoparticles Supported by Using Ammonium Salts of Hyperbranched Polystyrene: Preparation and Catalysis

Gold nanoparticles (1 nm in size) stabilized by ammonium salts of hyperbranched polystyrene are prepared. Selection of the R groups provides access to both water‐ and organo‐dispersible gold nanoparticles. The resulting gold nanoparticles are subjected to studies on catalysis in solution, which include reduction of 4‐nitrophenol with sodium borohydride, aerobic oxidation of alcohols, and homocoupling of phenylboronic acid. In the reduction of 4‐nitrophenol, the catalytic activity is clearly dependent on the size of the gold nanoparticles. For the aerobic oxidation of alcohols, two types of biphasic oxidation are achieved: one is the catalyst dispersing in the aqueous phase, whereas the other is in the organic phase. The catalysts are reusable more than four times without loss of the catalytic activity. Selective synthesis of biphenyl is achieved by the homocoupling of phenylboronic acid catalyzed by organo‐dispersible gold nanoparticles.     

Host-guest sensing by calixarenes on the surfaces

The present critical review reports on recent developments of optical nanoparticles based on the association of gold, silver, silica and quantum dots and calixarenes. These hybrid organic-inorganic compounds characterized by a thick organic layer self-assembled on the surface of a core of mineral surface atoms take advantage of the supramolecular recognition of luminescent calixarenes to fabricate nanodevices of nanoparticle size, capable of detecting metal cations, polyaromatic hydrocarbons and pesticides. Also presented is an explanation of the involvement of such nanoparticles in biochemical systems. This critical review provides an overview of their preparation, the manner in which they are characterized, and their use (108 references).     

Synthesis of Fused Oxazolocoumarins from o‐Hydroxynitrocoumarins and Benzyl Alcohol Under Gold Nanoparticles or FeCl3 Catalysis

Synthesis of fused oxazolocoumarins has been achieved from the one‐pot tandem reactions of o‐hydroxynitrocoumarins with benzyl alcohol in toluene under catalysis in a sealed tube at 150°C. The catalysis was performed by gold nanoparticles supported on TiO₂ (0.4 mol% Au) or FeCl₃ (5%) or silver nanoparticles supported on TiO₂ (1.7 mol% Ag).     

Synergistic effect in an Au-Ag alloy nanocatalyst: CO oxidation

Au-Ag alloy nanoparticles supported on mesoporous aluminosilicate have been prepared by one-pot synthesis using hexadecyltrimethylammonium bromide (CTAB) both as a stabilizing agent for nanoparticles and as a template for the formation of mesoporous structure. The formation of Au-Ag alloy nanoparticles was confirmed by X-ray diffraction (XRD), ultraviolet-visible (UV-vis) spectroscopy, and transmission electron microscopy (TEM). Although the Au-Ag alloy nanoparticles have a larger particle size than the monometallic gold particles, they exhibited exceptionally high activity in catalysis for low-temperature CO oxidation. Even at a low temperature of 250 K, the reaction rate can reach 8.7 x 10(-6) mol.g(cat.)(-1).s(-1) at an Au/Ag molar ratio of 3/1. While neither monometallic Au@MCM-41 nor Ag@MCM-41 shows activity at this temperature, the Au-Ag alloy system shows a strongly synergistic effect in high catalytic activity. In this alloy system, the size effect is no longer a critical factor, whereas Ag is believed to play a key role in the activation of oxygen.     

Gold catalysis in organic transformations: A review

This review updates the explosive development of gold catalysis for organic transformation focusing on the current literature over last 3 years. Recent investigations have shown that gold catalysis provides catalytically active systems, whereas selectivity and reusability are advantages over noncatalyzed organic transformations. The collected literature is focusing for new organic reactions and synthetic methodologies. Gold can also be suggested for green processes dedicated to fine chemicals, pharmaceuticals, and the food industry due to its recognized biocompatibility. The current review is focused on new methods in the organic synthesis that could be of interest in the wide area of organic chemistry for developing new catalytic pathways.     

Nanoparticles as recyclable catalysts: the frontier between homogeneous and heterogeneous catalysis

Interest in catalysis by metal nanoparticles (NPs) is increasing dramatically, as reflected by the large number of publications in the last five years. This field, "semi-heterogeneous catalysis", is at the frontier between homogeneous and heterogeneous catalysis, and progress has been made in the efficiency and selectivity of reactions and recovery and recyclability of the catalytic materials. Usually NP catalysts are prepared from a metal salt, a reducing agent, and a stabilizer and are supported on an oxide, charcoal, or a zeolite. Besides the polymers and oxides that used to be employed as standard, innovative stabilizers, media, and supports have appeared, such as dendrimers, specific ligands, ionic liquids, surfactants, membranes, carbon nanotubes, and a variety of oxides. Ligand-free procedures have provided remarkable results with extremely low metal loading. The Review presents the recent developments and the use of NP catalysis in organic synthesis, for example, in hydrogenation and C--C coupling reactions, and the heterogeneous oxidation of CO on gold NPs.     

Update on selective oxidation using gold

This critical review aims to update the recent development in the selective oxidation of organic compounds by gold catalysis, highlighting the progress in the last three years. Following the impressive developments in the last decades, several protocols for catalytic oxidation are today available, which are based on the extraordinary properties of gold in terms of catalytic activity, selectivity, reusability and resistance to poisons. Beside many other applications, gold can be recommended for green processes dedicated to fine chemicals, pharmaceuticals and the food industry owing to its recognized bio-compatibility. The collected literature is focused on experiments concerning the oxidation of different chemical groups and could be of interest, in the wide area of organic chemistry, for improving previous processes or for exploring new catalytic pathways (174 references).     

共价有机框架材料在多相催化领域的研究进展（英文）

共价有机框架(COFs)材料是近年来在拓扑学基础上发展起来的一类新型有机多孔聚合物,是有机单体通过可逆共价键连接而形成的晶型多孔材料,具有拓扑结构"可设计"、比表面积大、结构规整、孔道均一、孔径可调节以及易于修饰和功能化等优点.与金属有机框架材料(MOFs)相比,由于COFs是以共价键连接形成空间网络结构,具有较好的热稳定性和化学稳定性,又被称为"有机分子筛".COFs的构筑单体为有机小分子,有机小分子来源广泛而且种类繁多,使得构筑单体多样化,便于通过构筑单体来调控目标材料的结构和功能.自2005年首次报道以来,COFs以其独特的结构和优越的性能,吸引了广大科研工作者的极大兴趣,对其结构设计、可控合成、结构解析以及功能探索成为了研究热点,在气体吸附与分离、光电材料等领域展现出了广阔的应用前景.特别是在催化领域,由于COFs材料的多孔性、敞开的孔道结构、良好的稳定性以及易于修饰的特点,采用COFs作为催化剂以及催化剂载体受到了人们普遍的关注.作为催化剂,COFs可分为本征型催化剂和负载型催化剂.本征型催化剂的设计方法是基于"自下而上"策略将催化活性中心嵌入材料骨架之中;负载型催化剂的设计方法是以COFs为载体,通过后修饰方式负载金属颗粒或离子来构建多相催化剂.本征型COFs催化剂是在分子水平上引入催化活性中心,具有活性位点均匀分散、数量可控的特点,而且COFs规整均一的孔道结构有利于底物的传质,也为择形催化提供了可能;负载型催化剂通过后修饰方式引入催化活性中心,由于COFs以共价键连接,催化剂稳定性较高.COFs载体具有较大的比表面积,使得催化活性位点分散性好,也有利于底物与催化活性位点的结合.本文综述了COFs作为多相催化剂在催化领域的发展状况,按照COFs引入催化活性位点的类别,如单催化位点、双催化位点以及负载的金属纳米粒子进行了细致的阐述,重点讨论了COFs催化剂的设计理念、制备方式、功能化策略、材料的稳定性、催化活性以及选择性等内容.此外,对COFs作为光催化剂以及电催化剂方面的研究也进行了详细的介绍.最后,我们讨论了COFs在未来催化领域所面临的问题及挑战,并展望了COFs在超分子催化以及酶催化等方面的应用前景.     

Recent advances in gold-complex and chiral organocatalyst cooperative catalysis for asymmetric alkyne functionalization

Homogeneous gold catalysis has demonstrated the preponderant capability of realizing a broad range of synthetically versatile alkyne functionalization over the last two decades. Though catalytic asymmetric alkyne transformation has focused on the principle of using gold catalysts either associated with chiral phosphine ligand or combined with chiral counterion, a variety of breakthroughs have been reported with the application of gold-complex and chiral organocatalyst cooperative catalysis strategy, which could enable the challenging transformations that cannot be realized by mono-catalysis with excellent stereoselectivity. This review will cover two general protocols in this field, including relay catalysis and synergistic catalysis, with emphasis on the detailed cooperative catalysts models to illustrate the roles of the two catalysts and highlight the potential synthetic opportunities offered by asymmetric cooperative catalysis.     

Comparison study of the solution phase versus solid phase place exchange reactions in the controlled functionalization of gold nanoparticles

Gold nanoparticles offer tremendous potential in the areas of nanoelectronics, bio- and chemosensors, and catalysis. However, before these applications are realized, the surface functionality of nanoparticles must be better controlled. Our lab has recently reported a novel synthetic approach for making monofunctionalized nanoparticles through a solid phase place exchange reaction. Monofunctionalized gold nanoparticles may also be prepared through a solution phase place exchange reaction. In this study, we compared the efficiency of these two separate approaches toward controlled functionalization of gold nanoparticles by (1)H NMR, Fourier transform infrared (FT-IR), and transmission electron microscopy (TEM) analysis. We found that the solid phase place exchange approach is much more efficient at producing monofunctionalized gold nanoparticles. (1)H NMR data were used to give a semiquantitative count of substituted bifunctional ligands, and FT-IR spectra supported these findings. Furthermore, we used a diamine coupling reaction of nanoparticles to show the presence of single or multiple functional groups on the nanoparticle surface by TEM analysis.