Asymmetric reactions catalysed by polymeric cinchona alkaloids

Asymmetric catalysis by acrylonitrile-cinchona alkaloid copolymers (AN-CA) in Michaeltype reactions has been studied. The copolymers having a free amino alcohol part in the alkaloid moiety gave higher optical yields than other existing polymer-supported alkaloid catalysts. AN-CA catalysts were easily recovered from the reaction mixture with retention of enantioselectivity, a decided advantage over monometric catalysts. In some reactions AN-CA exhibited a distinct polymer effect which lead us to propose a new concept of stereo control: participation of C(3)-chirality in the enantioface differentiating step (C(3)-control). The catalytic behaviour of acrylamide-CA copolymer in asymmetric epoxidation under phase-transfer conditions was also studied.     

The use of soluble polymers to effect homogeneous catalyst separation and reuse

The use of soluble polymeric ligands for homogeneous catalysts separation is reviewed with emphasis on work from the author's laboratory. Examples discussed include polyethylene-bound catalysts, poly(alkene oxide)-bound catalysts, poly(N-isopropylacrylamide)-bound catalysts, fluorous polymer-bound catalysts and amphoteric polymer-bound catalysts. The utility of these systems is also discussed in the broader context of polymer-supported catalysis and the advantages and limitations of soluble polymeric ligands are discussed in this context.     

Polystyrene-supported acid catalysis

The present state of polymer-supported acid catalysis is considered. Models describing the catalytic action of gel-like and macroporous resin catalysts are presented. By chemical modification of poly (styrene-co-divinylbenzene) matrices, e.g. different ways of sulphonation, nitration, chlorination, fluorination and sulphoalkylation, the activity/selectivity and thermal stability of sulphonic acid resin catalysts can be improved. The synthesis of polymer-supported Lewis acids is described. By comparison to AlCl₃ higher catalytic activities are obtained with the use of AlBr₃.     

Polymer-supported aza-15-crown-5 as effective catalyst for phase-transfer reactions

Summary Immobilized aza-15-crown-5 were prepared by the reaction of chloromethylated polystyrene resin with N-(2-hydroxyethyl)-aza-15-crown-5. These polymer-supported crowns were very effective catalysts of nucleophilic substitution reactions carried out under the conditions of the two-phase (L-S) or three-phase (L-S-L) catalysis.     

Rational approach to polymer-supported catalysts: synergy between catalytic reaction mechanism and polymer design

Supported catalysis is emerging as a cornerstone of transition metal catalysis, as environmental awareness necessitates "green" methodologies and transition metal resources become scarcer and more expensive. Although these supported systems are quite useful, especially in their capacity for transition metal catalyst recycling and recovery, higher activity and selectivity have been elusive compared with nonsupported catalysts. This Account describes recent developments in polymer-supported metal-salen complexes, which often surpass nonsupported analogues in catalytic activity and selectivity, demonstrating the effectiveness of a systematic, logical approach to designing supported catalysts from a detailed understanding of the catalytic reaction mechanism. Over the past few decades, a large number of transition metal complex catalysts have been supported on a variety of materials ranging from polymers to mesoporous silica. In particular, soluble polymer supports are advantageous because of the development of controlled and living polymerization methods that are tolerant to a wide variety of functional groups, including controlled radical polymerizations and ring-opening metathesis polymerization. These methods allow for tuning the density and structure of the catalyst sites along the polymer chain, thereby enabling the development of structure-property relationships between a catalyst and its polymer support. The fine-tuning of the catalyst-support interface, in combination with a detailed understanding of catalytic reaction mechanisms, not only permits the generation of reusable and recyclable polymer-supported catalysts but also facilitates the design and realization of supported catalysts that are significantly more active and selective than their nonsupported counterparts. These superior supported catalysts are accessible through the optimization of four basic variables in their design: (i) polymer backbone rigidity, (ii) the nature of the linker, (iii) catalyst site density, and (iv) the nature of the catalyst attachment. Herein, we describe the design of polymer supports tuned to enhance the catalytic activity or decrease, or even eliminate, decomposition pathways of salen-based transition metal catalysts that follow either a monometallic or a bimetallic reaction mechanism. These findings result in the creation of some of the most active and selective salen catalysts in the literature.     

聚合物固载催化剂的研究进展

综述了近年来聚合物固载催化剂的研究进展。介绍的聚合物固载催化剂有6类，包括离子交换树脂催化剂、聚合物固载的相转移催化剂、聚合物固载的酸催化剂、聚合物固载的碱催化剂、聚合物固载的金属催化剂、聚合物固载的生物催化剂等。     

聚合物固载催化剂的研究进展

介绍聚合物固载催化剂有6类,包括离子交换树脂催化剂,聚合物固载的相转移催化剂,聚合物固载的酸催化剂,聚合物固载的碱催化剂,聚合物固载的金属催化剂,聚合物固载的生物催化剂等。综述了近年来聚合物固载催化剂的研究进展。     

联萘酚纳米孔道配位聚合物催化剂的研究进展

纳米多孔材料可用作催化剂、气体储存材料和光电子器件,是目前新型多孔材料的研究热点之一。手性联萘酚配体所修饰的催化剂是一种很优异的C2轴对称手性诱导源,可以催化各种α,β-不饱和羰基化合物,具有良好的催化活性和对映选择性。本文对由手性联萘酚类配体所修饰的小分子催化剂、聚合物负载的催化剂和自负载催化剂,在不饱和羰基化合物催化不对称环氧化反应中的应用进行了综述。本文介绍了对手性联萘酚纳米多孔配位聚合物的研究。     

Stability and recycling of polymer-supported Mo(VI) alkene epoxidation catalysts

As a prelude to commissioning a reactive distillation column (RDC) for the continuous epoxidation of cyclohexene using t-butylhydroperoxide and a heterogeneous polymer-supported Mo(VI) catalyst, the long-term stability of three candidate polymer-supported Mo catalysts has been evaluated. The polymer catalysts are a polybenzimidazole-supported species, PBI.Mo, and two poly(styrene-divinylbenzene) resin-based species, Ps.AMP.Mo1 and 2, prepared in-house by amination of vinyl benzyl chloride-containing resins using 2-aminomethyl pyridine, followed by loading with Mo. The stability of each polymer catalyst was assessed by recycling a sample 10 times in small batch reactions using conditions that will form the basis of the continuous process. At the same time the loss of Mo from each support has been investigated by isolating any residue from reaction supernatant solutions, following removal of the heterogeneous polymer catalyst, and then using the residues as potential catalysts in epoxidation reactions. This is a powerful technique for identifying unambiguously loss of catalytically active Mo from the support and is not dependent on Mo analytical procedures. All three polymer catalysts are highly active and selective in 10 consecutive reactions but the supernatant solutions also contain catalytically active Mo residues. In the case of PBI.Mo and Ps.AMP.Mo2 the contribution to catalysis from homogeneous Mo species lost from the supports is all but eliminated after aging through 10 cycles, but in the case of Ps.AMP.Mo1 the contribution from leached Mo species remains significant even after similar aging. The major factor determining this differential behaviour seems to be the mole ratio of polymer-bound ligand to Mo which must be significantly above unity to provide long-term retention of Mo.     

Polymer-supported N-heterocyclic carbene-iron(III) catalyst and its application to dehydration of fructose into 5-hydroxymethyl-2-furfural

Polymer-supported NHC–metal catalysts were prepared from chloromethyl polystyrene resin via two-step reaction. Metals were loaded into 1.6 – 16 mol% of total imidazolium and the remaining imidazolium chloride salt provided ionic liquid moiety. The formation of metal complex with the polymer-supported NHC ligand was analyzed by ATR FT-IR, XRD, and XPS. The synthesized polymer-supported NHC–metal catalysts were applied to the dehydration of fructose into HMF. The environmentally benign and inexpensive polymer-supported NHC–Fe^III catalyst showed good catalytic activity and yielded HMF at 73% (with a conversion of 97%). It could also be reused without significant loss of catalytic activity.     

可溶聚合物支载催化剂

可溶聚合物支载催化剂是当今“绿色化学”研究的热点问题之一。本文介绍了近几年来可溶聚合物支载催化剂,包括可溶聚乙二醇、可溶聚丙烯酰胺和可溶非交联聚苯乙烯支载催化剂的研究情况及其在有机合成中的应用。     

Hydrogenation of Citral Over a Polymer Fibre Catalyst

A polymer-supported Pd catalyst was investigated in hydrogenation of citral (3,7-dimethyl-2,6-octadienal), which is a stereoisomer with an isolated and a conjugated double bond as well as a carbonyl group. The catalyst was a fibrous polymer-supported catalyst modified with functional groups and immobilized metals. A comparison of the polymer-supported catalyst with conventional catalysts was made.     

The dicarbonylation and hydrodimerization of unsaturated hydrocarbons via heterogeneous palladium catalysis

Graphite and polymer-supported palladium catalysts, coupled with copper/lithium cocatalysts, have been found very effective for the oxidative carbonylation of unsaturated hydrocarbons. Hex-3-ene-1,6-dioate has been generated in 85% selectivity from 1,3-butadiene,-olefins yield dimethyl succinate derivatives. Butadiene hydrodimerization via analogous platinum catalysis selectively provides 1,6-octadiene, or 2,7-octadienyl formate. Mechanisms for the product selectivity are described.     

Phase-transfer catalytic activity of polymer-supported macrocyclic polyethers

Polymer-supported crown-ethers 9 and 11 (4.5-62% ring substitution) have been obtained by the reaction of 1% crosslinked chloromethylated polystyrenes with (hydroxymethyl) and (ω-hydroxynonyl)-18-crown-6, respectively. (Hydroxymethyl) and (ω-hydroxynonyl) [2.2.2] cryptands have also been prepared and linked in a similar way to afford catalysts 10 and 12 (3-6% ring substitution). Condensation of (aminomethyl) and (ω-aminodecyl [2.2.2] crypands with carboxylated 1% crosslinked polystyrene gave catalysts 13 and 14 (5-20% ring substitution). Phase-transfer catalytic activity of polymer-supported crown-ethers and cryptands has been tested in anion promoted nucleophilic aliphatic substitutions, and compared with that of polymer-supported phosphonium salts. The results indicate that catalytic activity of crown-ethers strongly depends on the combination of three parameters: the nature of the nucleophile, the percent ring substitution, and the presence of a spacer chain. Catalytic activity of cryptands is higher than that of crown-ethers and quaternary salts with similar percent ring substitution. It is much less dependent on the nature of the anions and on the presence of a spacer chain. As for the related quaternary salts, phase-transfer reactions promoted by polymer-supported crown-ethers and cryptands follow a mechanism identical with that observed for soluble catalysts: the reactions occur in the organic shell surrounding a complexed ligand; anions are exchanged at the water-organic solvent interface, the exchange not requiring the concomitant transfer of cationic counterparts.     

Functional mesoporous poly(ionic liquid)-based copolymer monoliths: From synthesis to catalysis and microporous carbon production

Ionic liquid-functionalized mesoporous polymeric networks with specific surface area up to 935 m²/g have been successfully synthesized one pot by solvothermal copolymerization of divinylbenzene and monomeric ionic liquids. The as-obtained polymers exhibit a monolithic structure featuring large pore volumes, an abundant mesoporosity and an adjustable content of ionic liquids. The effect of the reaction conditions on the pore structure has been studied in detail. These poly(ionic liquid)-based porous networks (PILPNs) have then been employed as precursors in two distinct applications, namely organocatalysis and production of microporous carbon monoliths. Selected organocatalyzed reactions, including carbonatation of propylene oxide by cycloaddition with carbon dioxide, benzoin condensation, and cyanosilylation of benzaldehyde have been readily triggered by PILPNs acting as crosslinked polymer-supported (pre)catalysts. The two latter reactions required the prior deprotonation of the imidazolium salt units with a strong base to successfully generate polymer-supported N-heterocyclic carbenes, referred to as poly(NHC)s. Facile recycling and reuse of polymer-supported (pre)catalysts was achieved by simple filtration owing to the heterogeneous reaction conditions. Furthermore, PILPNs could be easily converted into microporous carbon monoliths via CO₂ activation.     

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.     

Engineering selectivity into polymer-supported reagents for transition metal ion complex formation

Polymer-supported reagents are widely employed in the complexation of metal ions for applications in separations science, organic reactions (as catalysts) and in analytical chemistry (for processes requiring metal ion enrichment, detection and quantification). Various strategies for the continued development and optimization of polymer-supported reagents have evolved. This review cites ways in which polymer-supported reagents can be designed to achieve improved metal ion selectivities from the viewpoint of the mechanisms involved in the complexation of transition metal ions from aqueous solutions.     

Catalytic behaviors and gas permeation properties of palladium-containing phenophthalein poly(ether sulfone)

Palladiumsupported on a high-temperature-withstanding polymer, phenophthalein poly(ether sulfone) (PES-C), exhibits very high catalytic activity both in the carbonylation of allyl bromide and in the hydrogenation of 1-octene at 40°C and atmospheric pressure. The initial activities are up to 345 mol CO/mol Pd min and 493 mol H₂/mol Pd min, respectively. The polymer-supported palladium catalysts prepared by refluxing the mixture of PdCl₂ and PES-C immersed in benzene/ethanol (1/3, v/v) prior to the preparation of the catalyst show higher catalytic activity than those obtained by refluxing the mixture of PdCl₂ and PES-C in benzene/ethanol. The Pd-containing PES-C membranes made from the polymer-supported palladium catalysts are endowed with a very specific permeability of H₂ and the corresponding Pd-containing membrane catalysts can also exhibit considerable catalytic activity for the hydrogenation of 1-octene. © 1996 John Wiley & Sons, Inc.     

N-杂环卡宾催化Stetter反应的研究进展

N-杂环卡宾作为一类新型的催化剂,已广泛应用于有机合成领域.综述了N-杂环卡宾催化Stetter反应的研究进展,包括分子间的Stetter反应、分子内的Stetter反应、聚合物支撑的Stetter反应、Stetter-Paal-Knorr反应及其在天然产物合成中的应用.     

规整结构催化剂及反应器研究进展

介绍了一种新颖的规整结构催化剂。它在废气排放处理等气相催化反应中已表现出优于常规催化剂的优良催化性能,在气液固多相催化反应领域的研究也表明它能够应用于更多的催化反应。将这种催化剂和反应器结构特性与常规催化反应中应用的固体催化剂和反应器进行了比较,结果表明它有可能替代浆态床和固定床反应器,具有良好的应用前景。