Catalytic Enantioselective Flow Processes with Solid‐Supported Chiral Catalysts

Sustainability concerns are the wind in the sails for the development of novel, more selective catalytic processes. Hence, chiral catalysts play a crucial role in the green production of enantioenriched compounds. To further increase the green profile of this approach, the use of solid‐supported catalytic species is appealing due to the reduced generation of waste, as well as the possibility of reusing the precious catalyst. Even more attractive is the implementation of flow processes based on these immobilized catalysts, a flexible strategy that allows to generate from milli‐ to multi‐gram amounts of chiral product with a reduced footprint set‐up. Herein, we will present the efforts devoted in our laboratory towards the immobilization of chiral catalysts and their use in single‐pass, highly enantioselective, flow processes. Proline, diarylprolinols, other aminocatalysts, squaramides, thioureas, phosphoric acids and even chiral ligands and metal‐based catalysts constitute our current toolkit of supported species for enantioselective catalysis.     

Enantioselective hydrogenation of isophorone over Pd catalysts in the presence of(−)-dihydroapovincaminic acid ethyl ester: The effect of reduction method of Pd blacks on the enantiomeric excess

The enantioselective heterogeneous catalytic hydrogenation of isophorone in the presence of apovincaminic acid ethyl ester was investigated. Various Pd black catalysts differing in their preparation method were studied. The catalysts were characterized by different methods such as physical adsorption and chemisorption, SEM and XPS. An explanation was created for the different enantioselectivity of the catalysts being precipitated by different reducing agents.     

Enantioconvergent Substitution Reactions of Racemic Electrophiles by Organocatalysis

Over the past decades, the development of enantioselective catalysis using organocatalysts has evolved into an active research field and a number of enantioselective transformations have been established. However, despite their being a highly desirable process for the synthesis of organic molecules in an enantioenriched form, the enantioconvergent substitution reactions of racemic electrophiles using organocatalysts still present several challenges. Although intrinsic difficulties in the catalytic stereocontrol abound due to the initial chiral information of racemic electrophiles, in recent years, mechanistically diverse enantioconvergent processes have been intensively investigated in organocatalysis. This Minireview focuses on recent achievements in the development of enantioconvergent substitution reactions of racemic electrophiles using organocatalysts. The contents are classified on the basis of the mechanistic types of enantioconvergent processes.     

Rich chemistry of nitroso compounds

Nitrosobenzene or nitrosopyridine are found to be attractive electrophiles in catalytic enantioselective carbon-nitrogen and/or carbon-oxygen bond forming reactions. In the presence of designer Lewis or Br?nsted acid catalysts, catalytic enantioselective O- and N-nitroso aldol reaction or nitroso Diels-Alder reaction proceed smoothly. The scope and limitation of new catalytic processes are described.     

甲醇制备甲酸甲酯、甲缩醛和聚甲醛二甲醚的催化反应研究进展

由甲醇向下游衍生合成甲酸甲酯、甲缩醛和聚甲醛二甲醚等反应过程,不仅可以有效延伸甲醇产业链,消化业已形成的甲醇过剩产能,而且还可以带来巨大的经济和环境保护方面的效益,近年来受到研究者的广泛关注,与之相关的催化研究和开发也已取得长足的进步和发展。述评概述了近年来由甲醇出发制备甲酸甲酯、甲缩醛以及聚甲醛二甲醚等过程在催化剂制备和反应机理探索方面的研究进展,侧重介绍了贵金属催化剂上甲醇选择氧化制甲酸甲酯、钒基催化剂上甲醇选择氧化制甲缩醛以及分子筛催化剂上甲醇或甲缩醛与三聚甲醛合成聚甲醛二甲醚等催化反应过程。最后,对甲醇催化转化利用的未来发展方向进行了展望。     

氨合成催化剂及其催化反应机理研究进展

本文综述了氨合成这一最重要的工业多相催化过程80 多年来的研究进展。介绍了氨合成熔铁催化剂、氨合成钌催化剂的发展以及对氨合成催化反应机理的不同看法。     

纳米金催化剂上CO低（常）温氧化的研究

金历来被认为是催化惰性的,但近年来有关金催化剂的研究与开发引起人们的兴趣与关注。负载纳米金催化剂显示了良好的催化性能,尤其对一氧化碳氧化反应,能够在低（常）温下将CO氧化为CO₂。和其他CO氧化催化剂相比,金催化剂具有高的催化活性、稳定性和抗潮湿的性能,预示着更加广泛的应用前景。本文从制备方法、载体的性质、微粒粒径的大小、预处理、活性机理和催化反应机理等方面进行综合与评述。     

Chiral Organocatalysts in Enantioselective CO2 Utilization Reactions

The development of efficient CO₂ utilization reactions has gained a significant amount of attention in recent years. Although transformations of CO₂ to produce basic chemicals have been extensively investigated, the development of catalytic enantioselective CO₂ utilization reactions for the preparation of fine chemicals remains limited at this stage. Several excellent methods for catalytic enantioselective CO₂ utilization using chiral metal complex catalysts have been reported. Many researchers have also focused on developing organocatalyzed approaches to enantioselective CO₂ utilization, and several excellent examples have appeared in recent years. Herein, recent advances in catalytic enantioselective CO₂ utilization reactions using chiral organocatalysts are reviewed to provide a forecast for organocatalyzed enantioselective CO₂ utilization research.     

高分子负载催化剂的设计、合成及其在有机合成反应中的应用*

发展可回收和可重复利用的催化剂是过去几十年研究的一个热点,在这篇综述中,我们简要介绍了高分子负载催化剂的设计和合成策略以及这些催化剂在各种不同有机反应中的深入应用。在很多情况下,这一策略显示了它在产物的分离以及昂贵的催化剂的回收和再利用上的显著优点。与没有负载的同类催化剂相比,高分子负载的催化剂可以保持了同样的催化活性。另一方面,发展可控结构,尺寸,外观以及可溶性的线性聚合或树枝状的手性催化剂对于它们在有机合成中的应用都具有非常重要的意义。通过有机,高分子,以及材料化学家的共同努力,这一方法在跨学科间取得了很大的进展,这一发展对于决定载体的选择起到了很大的作用。因此,进一步发展高活性和高对映选择性的催化剂将仍然是这一领域的重要目标和挑战。     

Molecular complexes in water oxidation: Pre-catalysts or real catalysts

Artificial photosynthesis is considered a promising method to produce clean and renewable energy by sunlight. To accomplish this aim, development of efficient and robust catalysts for water oxidation and hydrogen production is extremely important. Owing to the advantages of easily modified structures and traceable catalytic processes, molecular water oxidation catalysts (WOCs) attract much attention during the past decade. However, the transformation of molecular WOCs to metal oxides/hydroxides or metal ions may occur under the harsh catalytic conditions, making the identification of true active species difficult. In this article, recent progress on molecular complexes acting as real catalysts or precursors toward water oxidation was briefly reviewed. We summarized the commonly used physical techniques and chemical methods that enable to distinguish homogeneous catalysts from heterogeneous catalysts. The factors that affect the nature of WOCs, such as reaction conditions, transition metal centers, and supporting ligands were discussed as well.     

Trost氮杂半冠醚手性配体在不对称催化反应中的应用

双功能手性金属络合物催化的不对称反应是目前有机化学研究的热点之一。本文综述了氮杂半冠醚手性配体与金属有机试剂络合的双金属催化剂,在催化不对称aldol反应、不对称Henry反应、不对称Michael反应、不对称Mannich反应、不对称Friedel-Crafts烷基化反应、不对称炔基化反应、不对称硅氰化反应、共聚反应、去对称化反应以及不对称Nozaki-Hiyama烯丙基化反应体系中的应用进展,重点介绍了不同催化体系对催化剂和反应底物之间立体效应和电子效应的影响,总结了控制反应立体选择性的规律以及有关催化反应的机理。     

Catalytic Asymmetric Hetero-Diels-Alder Reactions of Carbonyl Compounds and Imines

Asymmetric catalysis is a challenge for chemists: How can we design catalysts to achieve the goal of forming optically active compounds? This review provides the reader with an overview of the development of catalytic asymmetric hetero-Diels-Alder reactions of carbonyl compounds and imines. Since its discovery, the Diels-Alder reaction has undergone intensive development and is of fundamental importance for synthetic, physical, and theoretical chemists. The Diels-Alder reaction has been through different stages of development, and at the beginning of the 21st century catalytic Diels-Alder reactions are one of the main areas of focus. The preparation of numerous compounds of importance for our society is based on cycloaddition reactions to carbonyl compounds and imines. There are several parallels between the reactions of carbonyl compounds and those of imines, which, however, begin to vanish on entering the field of catalytic reactions. Why? From a mechanistic point of view some similarities can be drawn, but the synthetic development of catalytic enantioselective hetero-Diels-Alder reactions of imines are several years behind those of the carbonyl compounds. For hetero-Diels-Alder reactions of carbonyl compounds there a number of different chiral catalysts, and great progress has been achieved in developing enantioselective reactions for unactivated and activated carbonyl compounds. In contrast the development of catalytic enantioselective hetero-Diels-Alder reactions of imines is in its infancy and only few catalytic reactions have been published. This review will focus on the most important developments, and discuss the synthetic and mechanistic aspects of enantioselective hetero-Diels-Alder reactions of carbonyl compounds catalyzed by chiral Lewis acids. For the hetero-Diels-Alder reactions of imines, the diastereoselective reactions of optically substrates catalyzed by Lewis acids will be presented first, followed by the catalytic enantioselective reactions.     

新型后过滤金属烯烃聚合催化剂——镍系烯烃聚合催化剂

镍系烯烃聚合催化剂是近年来受到广泛关注的一类新型催化剂，是配位催化研究的热点之一。这类催化剂具有高催化活性、单活性中心和良好的分子剪栽性，可以在分子层次上实现烯烃聚合的分子设计与组装。本文介绍了镍系烯烃聚合催化剂的发展和研究概况，并评述了聚合特性及最新研究进展。     

新型后过渡金属烯烃聚合催化剂－－镍系烯烃聚合催化剂*

镍系烯烃聚合催化剂是近年来受到广泛关注的一类新型催化剂,是配位催化研究的热点之一。这类催化剂具有高催化活性、单活性中心和良好的分子剪栽性,可以在分子层次上实现烯烃聚合的分子设计与组装。本文介绍了镍系烯烃聚合催化剂的发展和研究概况,并评述了聚合特性及最新研究进展。     

Nanocarbons for Catalytic Desulfurization

Nanocarbon catalysts are green and sustainable alternatives to metal‐based catalysts for numerous catalytic transformations. The application of nanocarbons for environmental catalysis is an emerging research discipline and has undergone rapid development in recent years. In this focus review, we provide a critical analysis of state‐of‐the‐art nanocarbon catalysts for three different catalytic desulfurization processes. In particular, we focus on the advantages and limitations as well as the reaction mechanisms of the nanocarbon catalysts at the molecular level.     

Enantioselective C?C and C?H Bond Formation Mediated or Catalyzed by Chiral ebthi Complexes of Titanium and Zirconium

The development of catalytic processes that effect enantioselective bond formation under mild conditions is an important and challenging task in modern chemical synthesis. In this connection, chiral C₂-symmetric ansa-metallocenes (bridged metallocenes) have found notable applications as catalysts. This article discusses the chemistry of this class of chiral metallocene complexes with regard to their utility in catalytic and enantioselective C? C and C? H bond formation reactions. In addition, where applicable, a brief comparison with other related catalytic enantioselective processes is offered. Many of the reactions effected with high levels of enantioselectivity by catalytic amounts of these complexes are of great significance to the preparation of new materials and in the synthesis of therapeutic agents. For example, zirconocene complexes readily catalyze the enantioselective addition of alkylmagnesium halides to alkenes, and cationic zirconocene complexes may promote the highly stereoregulated copolymerization of terminal alkenes. Furthermore, the related chiral titanocenes are involved in an impressive range of useful asymmetric catalytic reactions, including the enantioselective hydrogenation of olefins and reduction of imines or ketones. This review attempts to bring together the practical aspects of the use of [(ebthi)M] complexes of Group 4 transition metals (catalyst synthesis and resolution), outline the manner in which the C₂-symmetric chiral ligands are believed to initiate stereoselective bond formation, and highlight the aspects of this chemistry that are less well understood and require further research.     

Enantioselective organocatalytic intramolecular Diels-Alder reactions. The asymmetric synthesis of solanapyrone D

The first direct enantioselective organocatalytic intramolecular Diels-Alder reaction has been accomplished. The use of iminium catalysis has provided a new catalytic strategy for the enantioselective [4 + 2] cycloisomerization of a wide variety of tethered diene-enal systems. The use of imidazolidinones 1 and 2 as the asymmetric catalysts has been found to mediate the enantioselective construction of [4.4.0] and [4.3.0] ring systems. Application of this methodology to the highly efficient asymmetric synthesis of the marine metabolite solanpyrone D has also been accomplished. A diverse spectrum of aldehyde substrates can also be accommodated in this new organocatalytic transformation. Importantly, this technology has been utilized to execute the first enantioselective, catalytic Type II IMDA reaction.     

非均相催化烯烃交叉复分解反应

烯烃交叉复分解反应作为石油化工领域一种重要过程,为各种单烯烃间的互相转化提供了一条有效的途径。特别是在利用正丁烯生产丙烯和其它重要单烯烃方面,复分解反应受到越来越多的重视。本文对烯烃交叉复分解反应(CM)的进展进行了综述,讨论了CM各种工艺的技术特点及反应机理,重点介绍了WO₃/SiO₂、Re₂O₇/Al₂O₃、MoO₃/Al₂O₃3类催化剂的最新改进及相应的理论分析,试图理清催化剂今后发展的思路,为进一步改进催化剂的性能提供相关的依据。     

Dendrons and dendritic catalysts immobilized on solid support: Synthesis and dendritic effects in catalysis

Dendrimers, the aesthetically beautiful macromolecules displaying a variety of potentially useful architecture‐induced properties, are traditionally assembled in solution. However, since 1988, a number of dendritic structures have been assembled on insoluble organic and inorganic polymers, and thus dendronized supports have been formed. One of the major applications of these new materials is in the field of heterogeneous catalysis. Supported dendritic catalytic systems, bearing the catalytic units on the dendron periphery, have been examined in the last 5 years in such reactions as hydroformylation, Heck and other Pd‐catalyzed C? C bond formations, oxidation, and enantioselective addition to aldehydes. In the majority of these studies, substantial dendritic effects on the reactivity, selectivity, or recyclability of the catalysts were observed. Although a number of factors have been suggested as sources of the effects, it is most likely that the phenomenon has a multicomponent origin. Additional research, including a full determination of the effects and their causes, is likely to lead to markedly better heterogeneous catalytic systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 235–262, 2005     

Hot electron generation on metal catalysts under surface reaction: Principles,devices, and application

Transfer of charge through metal-support interfaces leads to an increase in the activity of mixed catalysts. In this review, we consider the main aspects of research aimed at studying processes that create and allow interphase transfer of highly excited (hot) charge carriers in supported catalysts, and discuss the effect of these phenomena on catalytic activity.