The Clicked Pyridyl‐Triazole Ligand: From Homogeneous to Robust,Recyclable Heterogeneous Mono‐ and Polymetallic Palladium Catalysts for Efficient Suzuki–Miyaura,Sonogashira, and Heck Reactions

Various mono‐ and polymetallic palladium complexes containing a 2‐pyridyl‐1,2,3‐triazole (pyta) ligand or a nonabranch‐derived (nonapyta) ligand have been synthesized by reaction of palladium acetate with these ligands according to a 1:1 metal‐ligand stoichiometry and used as catalysts for carbon‐carbon cross‐coupling including the Suzuki–Miyaura, Sonogashira and Heck reactions. The unsubstituted monopalladium and nonapalladium complexes were insoluble in all the reaction media, whereas tri‐ and tetranuclar palladium complexes were soluble, which allowed conducting catalysis under either homogeneous or heterogeneous conditions. The organopalladium complexes were characterized by standard analytical and spectroscopic methods and by thermogravimetry showing decomposition above 110 °C. Both types of catalysts showed excellent activity for these cross carbon‐carbon bond formations involving aryl halides including activated aryl chlorides or acyl chloride. Besides the comparison between homogeneous and heterogeneous catalysis, the key feature of these catalysts is their remarkable robustness that allowed recycling at least ten times in the example of the Heck reaction with excellent yields and without significant reduction of the conversion.     

Comparison of immobilized Box and azaBox–Cu(II) complexes as catalysts for enantioselective Mukaiyama aldol reactions

Enantioselective Mukaiyama aldol reactions of different α-ketoesters was tested with copper complexes of chiral Box and azaBox ligands in both homogeneous and heterogeneous systems. Results in the homogeneous reactions were greatly influenced by the nature of the ketoester, the chiral ligand, and the reaction solvent. In the case of supported catalysts, the use of strongly coordinating azaBox ligands prevented the leaching of metal but reduced the Lewis acidity, and thus the catalytic activity, and did not solve the problem of poisoning by strong coordination of products, byproducts, or solvents. The counter-ion effect also was very significant, and electrostatic immobilization was efficient only with Box ligands (up to 86% ee at room temperature), whereas covalent immobilization allowed the use of azaBox ligands (up to 85% ee at room temperature) in the heterogeneous phase. Recovered deactivated solids could be reused in a reaction with a completely different mechanism that does not require acid centers, such as cyclopropanation.     

In situ XAFS Characterization of Supported Homogeneous Catalysts

Heterogenization of homogeneous catalysts explores the cross-fertilization of homogeneous and heterogeneous catalysts to combine most of their advantages. The molecular dispersion of active sites in these materials limits the application of conventional spectroscopic techniques utilized for the characterization of heterogeneous catalysts. The X-ray absorption spectroscopy is the most suitable tool to characterize the molecular species present in these catalysts because this technique is sensitive to short-range structural orders, element-specific and amenable to in situ studies. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies for selective examples of supported homogeneous catalysts are reviewed. Supported liquid phase catalysts (supported Wacker-type catalysts for CO oxidation), intercalated homogeneous catalysts, supported metal complexes for the olefin polymerization and tethered homogeneous catalysts are included.     

负载液相催化剂的研究进展

负载液相催化剂是一种新型的“混合型”催化剂,它结合了均相催化高活性、高选择性和多相催化接触面积大、容易分离的优点,有广阔的应用前景。综述了迄今为止关于负载液相催化剂的研究进展,总结了负载液相催化剂的特点及其在许多重要化学反应中的应用。     

Environmentally benign multiphase catalysis with dense phase carbon dioxide

Environmental concerns stemming from the use of conventional solvents and from hazardous waste generation have propelled research efforts aimed at developing benign chemical processing techniques that either eliminate or significantly mitigate pollution at the source. This paper provides an overview of heterogeneous and homogeneous catalysis in dense phase CO₂, considered a green solvent. In addition to solvent replacement, the demonstrated advantages of using dense phase CO₂ include the enhanced miscibility of reactants, such as O₂ and H₂ which eliminate interphase transport limitations, and the chemical inertness of CO₂. Further, the physicochemical properties of CO₂-based reaction media can be pressure-tuned to obtain unique fluid properties (e.g. gas-like transport properties, liquid-like solvent power and heat capacities). The advantages of CO₂-based reaction media for optimizing catalyst activity and product selectivity are highlighted for a variety of reactions including alkylation on solid-acid catalysts, hydrogenation on supported noble metal catalysts and a broad range of homogeneous oxidations with transition metal catalysts and dioxygen as an oxidant. Through these examples, the need is emphasized for a systematic approach to research and development of supercritical carbon dioxide based processes, taking into account conventional multiphase reaction engineering principles, catalytic chemistry and phase behavior.     

纳米多相催化材料在常温反应中的应用

近年来,纳米材料在化学反应过程中扮演着越来越重要的角色。纳米材料作为多相催化剂,具有高活性、高选择性、高稳定性而且易于回收利用等优点。将精心设计的纳米材料用于催化一系列反应,使其在常温下进行,可以促进资源的高效利用和节能减排,在化工领域有着广阔的应用前景。本文详细介绍了以下几种类型的纳米材料,即金属纳米粒子材料、固载型金属离子复合物纳米材料、金属氧化物纳米材料和固体酸纳米材料。并阐述了上述纳米材料的结构特点及在催化方面的优势,同时结合实例,着重探讨了上述纳米材料作为多相催化剂在氧化反应、还原反应、偶联反应等多种节能高效反应中的应用。纳米材料因其多方面的优点以及广阔的应用范围,是一种极具发展潜力的多相催化材料。     

Supported ionic liquids: versatile reaction and separation media

The latest developments in supported ionic liquid phase (SILP) systems for catalysis and separation technology are surveyed. The SILP concept combines the advantages of homogeneous catalysis with heterogeneous process technology, and a variety of reactions have been studied where supported ionic liquid catalysts proved to be more active and selective than common systems. In separation applications the use of supported ionic liquids can facilitate selective transport of substrates across membranes.     

非均相金属钯配体催化剂的研究进展

Suzuki-Miyaura反应是一类具有工业化应用前景的C-C键合成反应。反应多数是在均相金属钯配体催化剂催化下完成。均相催化具有催化效率高、产品选择性好等优点,但催化剂回收困难,增加了反应成本,限制了其应用。非均相金属钯配体催化剂是将均相金属钯配体催化剂固载到载体上,使其在不影响反应活性和选择性的同时,实现循环使用,已成为Suzuki-Miyau-ra反应的研究热点。对几年来以有序介孔材料MCM-41和SBA-15、无机载体SiO2和Al2O3、聚苯乙烯和聚乙二醇等合成材料以及天然高分子材料为载体,制备非均相金属钯配体催化剂的方法及其催化性能进行了综述。     

Development of a continuous process for the hydroformylation of long-chain olefins in aqueous multiphase systems

The challenging task of homogeneous catalysis is the efficient combination of reaction and catalyst recycling. In the hydroformylation of long-chain olefins generally cobalt-based catalysts are used, but in our investigation we used rhodium-based catalysts, because of their higher activity in comparison to cobalt catalysts. In hydroformylation reactions, the recycling of the expensive rhodium catalyst as well as the selectivity to linear aldehydes are very challenging. Multiphase systems offer the possibility to increase the interfacial area during reaction on the one hand and to separate the metal–ligand complexes easily from the organic product phase after reaction, to recycle the expensive catalyst for further reactions, on the other hand. Solubilisers such as surfactants or polar solvents can be used to formulate such a tuneable solvent system. Upon cooling of the reaction mixture, phase separation is achieved. Based on that combination of reaction and phase separation for catalyst recycling, a novel process concept was developed for the hydroformylation of long-chain olefins. In order to show the applicability of that concept in a continuous process a fully automated miniplant was designed.     

Attempts to Fill the Gap Between Enzymatic, Homogeneous, and Heterogeneous Catalysis

Bio-inspired and single site metal complex catalysts have been discussed to direct towards a rational design of solid heterogeneous catalysts. When concepts derived from catalytic antibodies, molecular imprinting and molecular recognition, and site isolation and modification by appropriate ligands are combined, with new techniques to prepare, tailor made solid materials, catalysts can be prepared that improve reaction rate and selectivity by increasing the concentration and activation of reactants in the vicinity of the active sites, and by stabilizing transition states or intermediate products. It is also shown that enzymatic, homogeneous and hetergeneous catalysts can be combined to perform “one-pot” cascade reactions.     

Heck reactions catalyzed by oxide-supported palladium – structure–activity relationships

The catalytic activity and selectivity of palladium supported on various metal oxides in carbon–carbon coupling reactions of aryl bromides with styrene (Heck reaction) were investigated. The activity is determined by the nature of the oxide support and the Pd dispersion (structure–activity relationships). The relation of homogeneous (leaching) and heterogeneous mechanisms is discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Poly(norbornene)‐Supported N‐Heterocyclic Carbenes as Ligands in Catalysis

In this contribution, we present the synthesis of norbornene‐supported N‐heterocyclic (NHC) carbenes. These functionalized norbornenes were polymerized via ring‐opening metathesis polymerization in a controlled fashion either before or after metalation with a variety of palladium and ruthenium precursors resulting in the formation of polymer‐supported NHC‐based metal catalysts. The activities of the palladium‐based catalysts in the Suzuki–Miyaura, Sonogashira and Heck coupling reactions were studied in detail. In all cases, the polymeric catalysts demonstrated the same activity as their small molecule analogues. Furthermore, we carried out preliminary investigations into the stability of these catalysts using poisoning studies. A clear dependence of the stability of the polymer‐supported catalysts on their palladium precursor was observed with palladium acetate‐based polymeric NHC catalysts being the most stable. Finally, we have studied the reactivity of our supported NHC ruthenium complexes as catalysts for ring‐closing metathesis. Again, in all cases good conversions were observed with comparable activities to other supported NHC‐ruthenium catalysts. Lastly, we were able to remove the ruthenium catalysts from the solution quantitatively demonstrating the possibility of metal removal.     

Reaktions- und verfahrenstechnische Aspekte der Heterogenisierung homogen-katalysierter Synthesen

Reaction and process engineering aspects of transforming homogenous catalytic syntheses into heterogeneous processes. In order to avoid the separation of the catalyst in homogeneous catalytic processes, the preparation of supported phase catalysts has attracted widespread attention in recent years. Most interest has focussed on the immobilization of transition-metal complexes on solid supports for catalyzing carbon monoxide and olefin reactions. After a survey of the development of solid supported phase (SSP)- and supported liquid phase (SLP)-catalysts two reactions in which SSP-catalysts have been applied are considered in detail: The carbonylation of methyl acetate to acetic anhydride and the stereoselective hydrogenation of 2-acylaminocinnamic acid to (S)-phenylalanine, a derivative of L -DOPA. In order to discuss the favourable characteristics and the disadvantages of SSP-catalysts, they are compared to soluble catalysts. Furthermore, the design of both processes is discussed.     

Liquid–Liquid Phase Transfer Catalysis: Basic Principles and Synthetic Applications

Abstract

Bio‐inspired and single site metal complex catalysts have been discussed to direct towards a rational design of solid heterogeneous catalysts. When concepts derived from catalytic antibodies, molecular imprinting and molecular recognition, and site isolation and modification by appropriate ligands are combined, with new techniques to prepare, tailor made solid materials, catalysts can be prepared that improve reaction rate and selectivity by increasing the concentration and activation of reactants in the vicinity of the active sites, and by stabilizing transition states or intermediate products. It is also shown that enzymatic, homogeneous and hetergeneous catalysts can be combined to perform “one‐pot” cascade reactions.     

Vanadium Complexes Based Polymer Supported Catalysts: A Brief Account of Research from Our Group

Solid supported catalysts can go a long way in developing catalyst based technology because of their high efficiency with recyclability and easy separation from the reaction mixture. Immobilizations of homogeneous catalysts through covalent bond with chloromethylated polystyrene cross-linked with divinylbenzene and develop them as environmentally safe heterogeneous catalysts for oxidation reaction have attracted attention in recent years. Recently, effort from our research laboratory was to synthesize new recyclable polymer-supported vanadium complexes based heterogeneous catalysts. Thus, chloromethylated polystyrene cross linked with 5% divinylbenzene was used as support to prepare variety of polymer supported vanadium catalysts. These catalysts have successfully been used for the oxidation and oxidative bromination of various organic substrates. Keeping in mind the industrial usage of these heterogeneous catalysts, the leaching and recycle ability of all polymer-supported catalysts have also been tested. Most catalysts are stable and do not leach during the catalytic reactions.     

Oxidative Heck Coupling Using Pd(II) Supported on Organosilane-Functionalized Silica Mesocellular Foam

Oxidative Heck couplings of arylboronic acids and olefins are carried out under air to facilitate reoxidation of palladium without the need for an added co-oxidant using Pd(II) supported on silica surface-tethered bipyridyl, iminopyridine, or 3-aminopropyl ligands. Use of silica-supported iminopyridine or bipyridine ligands gives active catalysts, with the bipyridine-based catalyst being most efficient. The Heck products are formed with high yields and selectivities over the 1,4-addition product, and the silica supported bipyridine-based catalyst is easily recovered via simple filtration. Unlike similar supported catalysts in traditional Heck reactions involving aryl halides and olefins, the catalysts presented here can be used for multiple catalytic cycles without activity or selectivity loss.     

Microgels as new support materials for heterogeneous cocatalysts in ethylene polymerization reactions

Microgels are monodisperse poly(organosiloxane) microparticles that can be functionalized at their surface. These materials were tested as supports for heterogeneous cocatalysts of the methylaluminoxane type and were used for the polymerizations of olefins with transition‐metal catalysts. The cocatalysts were synthesized directly on the surfaces of the microgel particles by the partial hydrolysis of trimethylaluminum and were then used for the activation of homogeneous catalyst precursors. Complexes of various chemical natures were successfully activated and optimized through variations in the Al/H₂O ratio used for the synthesis. Metallocene dichloride complexes and coordination compounds of iron and nickel were tested as catalysts for ethylene polymerization, and the results were compared with the results for the homogeneous systems and heterogeneous systems supported on silica gel (SiO₂). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3021–3029, 2002     

Synthesis of condensation polymers catalyzed by palladium-graphite

Palladium-graphite (Pd---Gr) was applied to polycondensations as a heterogeneous palladium catalyst. Catalytic activities of Pd---Gr for the Heck reaction and a carbonyl insertion reaction were investigated using the model reactions. Polycinnamamide was synthesized through the Heck reaction of N, N′-(3,4′-oxydiphenylene)bis(acrylamide) and bis(4-iodophenyl) ether catalyzed by Pd---Gr. The polymerization proceeded efficiently in the presence of tributylamine, but required a long reaction time compared with the case of homogeneous catalysts. The resulting polymer was almost white in color, which means that it was less contaminated by palladium metal. The removal and recycling of Pd---Gr were much easier than the case of homogeneous catalysts. Aramid was also synthesized through the carbonyl insertion reaction of m-diiodobenzene and bis(4-aminophenyl) ether catalyzed by Pd---Gr. The rate of carbon monoxide consumption for the polymerization catalyzed by Pd---Gr was almost equal to that catalyzed by the homogeneous palladium catalyst. In both cases, the structures of the resulting polymers were identical to those prepared by homogeneous palladium catalysts.     

Model Systems in Heterogeneous Catalysis: Selectivity Studies at the Atomic Level

Reaching 100% selectivity is the theme of the twentyfirst century in heterogeneous and heterogenized homogeneous catalysis. To study chemical reactivity at the atomic scale, model systems have been prepared and characterized. We discuss selectivity of hydrogenation and dehydrogenation reactions on supported Pd particles, methanol oxidation at vanadium oxide model catalysts and, at last, the design of model catalysts with a well defined charge state of the metal, i.e., Au catalyst model systems.     

羰基化合物直接还原胺化合成伯胺催化剂研究进展

胺类化合物是一类重要的化工原料和中间体，在农药、医药、染料、高分子聚合物等领域有着广泛的应用。通过羰基化合物（醛或酮类）的还原胺化来制备胺类化合物是当前的研究热点。研究表明，贵金属基和非贵金属基的多相和均相催化剂均能够高效催化醛或酮类的还原胺化反应。本文对近年来羰基化合物直接还原胺化（或一锅法）合成伯胺的研究现状进行了综述，包括还原胺化反应、催化剂、反应条件、底物适用范围和催化作用机制等，其中重点阐述了直接还原胺化催化剂的研究进展。文章指出：通常多相催化剂具有活性高以及可重复使用等优点，而均相催化剂的优势在于催化效率高，伯胺选择性高；另一方面，以Pd、Rh、Ru等为代表的贵金属催化剂催化性能优异，但价格昂贵，因此可采用Co、Ni等性能同样优异但价格相对低廉的非贵金属催化剂以降低成本。文中提出，催化效率高、反应条件温和、普适性高的羰基化合物还原胺化催化剂应成为未来重点研究方向。