Dendronized Poly(Ru‐BINAP) Complexes: Highly Effective and Easily Recyclable Catalysts For Asymmetric Hydrogenation

A new kind of dendronized polymeric chiral BINAP ligands has been synthesized and applied to the Ru‐catalyzed asymmetric hydrogenation of simple aryl ketones and 2‐arylacrylic acids. These dendronized poly(Ru‐BINAP) catalysts exhibited high catalytic activity and enantioselectivity, very similar to those obtained with the corresponding parent Ru(BINAP) and the Ru(BINAP)‐cored dendrimers. It was found that the pendant dendrons had a major impact on the solubility and the catalytic properties of the polymeric ligands. These polymeric catalysts could be easily recovered from the reaction solution by using solvent precipitation, and the reused catalyst showed no loss of activity or enantioselectivity.     

Studies on immobilized polymer-bound imidazole copper(II) complexes as catalysts. Part II. immobilization of copper(II) complexes of poly(styrene-co-n-vinylimidazole) by quaternization or adsorption on silica and their catalyses of oxidative coupling of 2,6-disubstituted phenols

Copper(II) complexes of poly(styrene-co-N-vinylimidazole) (Cu(II)-PS-im) were immobilized on modified silica by quaternization or on unmodified silica by adsorption and these immobilized polymer-bound complexes were applied as catalysts for oxidative coupling polymerization of 2,6-dimethylphenol (DMP) in toluene / methanol (13 / 2 v / v). Higher average chain loading (α) of PS-im with imidazole groups, e.g. a ⩾ 17%, was essential for successful adsorption. A main role of hydroxide appears to be production of more reactive phenolate anions from DMP. A rise in reaction rate was not observed for high ligand / Cu, which probably resulted from too high viscosity of the silica suspension at high ligand / Cu. In a batch process under comparable conditions both types of immobilized polymer catalysts were found to have the same preference for poly-2,6-dimethyl-1,4-phenyleneoxide formation as non-immobilized Cu(II)-PS-im and their low molar mass analogue. However, they were five times less active than non-immobilized ones, which was explained primarily in terms of a reduced effective ligand / Cu ratio after the immobilization of polymeric ligands. Application of both types of immobilized polymer catalysts in a continuous stirred tank reactor (CSTR) for oxidative coupling of 2,6-di-tert-butylphenol was successful. A stable phenol conversion was obtained in CSTR under suitable conditions for at least 120 hours.     

Polymer-supported molybdenum and vanadium catalysts for epoxidation of alkenes by alkyl hydroperoxides

Polymer-supported molybdenum and vanadium catalysts were synthesized using gel-type crosslinked copolymers with microheterogeneous structure. The supports were composed of inert ethylene–propylene rubber and crosslinked high molecular weight poly(ethylene oxide) matrices and polymeric ligands grafted or forming interpenetrating networks: poly(acrylic acid), poly(methacrylic acid), poly(4-vinylpyridine), and polyvinyl alcohol. Catalytic activity and selectivity of some of these complexes were tested in epoxidation of styrene by ethylbenzene hydroperoxide. Molybdenyl cations are strongly coordinated with pyridine-containing copolymers giving catalysts of high activity and selectivity. They provide conversion and selectivity above 70%. Because of the microheterogeneous mosaic-like structure of the supports, better accessibility of the active sites is achieved.     

Designing Phase Selectively Soluble Polymer-Supports for Dimethylaminopyridine and Phosphine-Ligated Pd(0) Catalysts

Soluble poly(4-alkylstyrene) containing 4-methyl-, 4-tert-butyl, 4-dodecyl-, and 4-octadecylstyrene were formed either with monomers containing dyes-, ligands, or catalysts or with 5–10 mol% of 4-chloromethylstyrene and studied as supports for ligands or catalysts. Studies with dye-labeled polymers showed that polymers containing longer alkyl groups alone or at ca. 10 mol% loading are highly soluble in heptane can be used to separate and recycle organo- and transition metal catalysts.     

Designing Phase Selectively Soluble Polymer-Supports for Dimethylaminopyridine and Phosphine-Ligated Pd(0) Catalysts

Soluble poly(4-alkylstyrene) containing 4-methyl-, 4-tert-butyl, 4-dodecyl-, and 4-octadecylstyrene were formed either with monomers containing dyes-, ligands, or catalysts or with 5–10 mol% of 4-chloromethylstyrene and studied as supports for ligands or catalysts. Studies with dye-labeled polymers showed that polymers containing longer alkyl groups alone or at ca. 10 mol% loading are highly soluble in heptane can be used to separate and recycle organo- and transition metal catalysts.

     

Recent Advances in Asymmetric C?C and C‐Heteroatom Bond Forming Reactions using Polymer‐Bound Catalysts

The synthesis of enantiomerically pure compounds is one of the major challenges in organic synthesis. In this review, we present the state of the art in asymmetric catalysis using immobilized chiral ligands and complexes for asymmetric C C and C‐heteroatom bond forming reactions. Chiral catalysts based on dendrimers and soluble polymeric supports are considered. In particular, addition reactions to carbon‐carbon double bonds, asymmetric 1,2‐addition reactions using, e.g., dialkylzinc reagents, metal‐catalyzed substitution reactions and cycloaddition reactions are covered. Specific emphasis is placed on enantioselective epoxidation and aldol reactions. A further aspect is the (hetero) Diels–Alder reaction catalyzed by immobilized ligands.     

The synthesis and characterization of polymer-bound diaryliodonium salts and their use in photo and thermally initiated cationic polymerization

Summary A new method for the synthesis of polymer-bound diaryliodonium salts has been developed which facilitates the preparation of these polymeric initiators. The polymer-bound diaryliodonium salts were used in both photo and thermally initiated cationic polymerizations.     

Chemical modification of polystyrene

Summary Sulfinate functional groups have been introduced on selected positions of the aromatic rings of soluble or crosslinked polystyrene via lithiation reactions followed by quenching with sulfur dioxide. The sulfinate polymers have good stability, can be stored at room temperature, and can be used for ion-exchange or as nucleophiles to produce polymer-bound sulfones. Good functional yields of polystyrene resins with sulfone pendant groups can be obtained by reaction of the polymeric sulfinates with various alkyl halides under phase transfer or classical conditions.     

Transition metal complexes bound to macroporous resins carrying nitrile groups. Effect of matrix structure on the activity of supported catalysts

Two groups of resins bearing nitrile (CN) groups based on macroporous copolymers of acrylonitrile and divinylbenzene (AN/DVB) and terpolymers of styrene, acrylonitrile and divinylbenzene (S/AN/DVB) have been used as polymer matrices for the immobilization of Rh(I), Pt(II) and Pd(II) complexes. A group of four S/DVB resins functionalized with the CN ligands have been prepared and used for comparison. The resins differ in their chemical and physical structure, local concentration of the CN groups and their availability. Characterization of the heterogeneous complexes by IR spectroscopy confirmed the coordination of the metal ions to the polymer-CN ligands. The catalytic behaviour of the immobilized complex catalysts was tested in the hydrosilylation of 1-hexene. The activity of the polymer-bound catalysts strongly depends on the structure of the support used. The largest effect of the chemical structure of the polymer was found for the catalysts immobilized on the AN/DVB resins, while the polymer morphology played the major role in the high activity of the catalysts attached to the S/N/DVB resins. Lower activity was found for the systems bound to the functionalized S/DVB resins. Both polymer-supported Pt and Rh systems appeared to be highly effective for the hydrosilylation of the CC double bonds, but the platinum catalysts proved to be considerably more active. The rhodium catalysts were found efficient in the hydrosilylation of ketones. The immobilized Pd(II) complex was reduced to the metallic Pd by hydrosilanes. The supported Pt catalyst remained active when recycled 5 times, while the activity of the rhodium systems gradually decreased. The results offer the possibility of choosing the most suitable polymer matrix for the immobilization of metal complex catalysts for use in hydrosilylation and other catalytic reactions.     

Comparative studies on the performance of immobilized quaternary ammonium salt catalysts for the addition of carbon dioxide to glycidyl methacrylate

The addition of carbon dioxide to glycidyl methacrylate (GMA) was investigated in a semi-batch reactor using immobilized quaternary ammonium chloride catalysts. Five different catalysts were prepared with the following supports: (1) soluble poly(ST-co-VBC)[C1], (2) insoluble poly(ST-DVB-VBC)[C2], (3) macroporous poly(ST-DVB-VBC)[C3], (4) poly(ST-co-VBC)-MMT[C4], (5) modified MCM-41[C5]. The addition of carbon dioxide to GMA can be considered as pseudo first-order with the concentration of GMA. The soluble poly(ST-co-VBC)-supported catalyst containing benzyltributylammonium chloride group showed the highest reaction rate. The order of the pseudo first-order rate constant for the catalysts was C1 > C3 > C2 > C4 > C5. The activation energy for the C1–C5 catalysts was 11.5, 28.1, 20.8, 36.6 and 39.3 kJ/mol, respectively. The immobilized catalysts can be reused for at least four successive runs without any considerable loss of their initial reactivities.     

Comparison of water permeation behaviour in poly(dimethylsiloxane), poly(ether ether ketone), and glass fibre reinforced composites using dielectric spectroscopy

Abstract

This paper describes the use of dielectric spectroscopy to characterise the absorption of water by three different classes of polymeric materials: an elastomer, poly(dimethylsiloxane); a thermoplastic, poly(ether ether ketone); and two composites, polyester and vinyl ester glass fibre reinforced laminates (GRP). Novel approaches have been used to assess water absorption by the elastomer and the GRP and the results are critically assessed. The data for all the materials are discussed in the context of their molecular structures. The applicability and limitations of these dielectric methods for the assessment of water absorption in polymeric materials that have considerably different physical properties is demonstrated.     

Engineering Polymer‐Enhanced Bimetallic Cooperative Interactions in the Hydrolytic Kinetic Resolution of Epoxides

Through systematic variations of the length of oligo(ethylene glycol)‐based linkers and the catalyst density of poly(styrene)‐supported cobalt‐salen catalysts, we have elucidated an optimal catalyst flexibility and density of polymeric Co‐salen catalysts for the hydrolytic kinetic resolution (HKR) of racemic terminal epoxides that follows a bimetallic cooperative pathway. The optimized polymeric catalyst brings the two cooperative Co‐salen units to a favorable proximity efficiently and hence displays significantly improved catalytic performance in the HKR compared with its monomeric small molecule analogue. Complex Co(5b) , representing the most active poly(styrene)‐supported HKR catalyst known so far, can effect the resolution of a variety of epoxides to reach ≥98 % ee in 6–24 h with a low cobalt loading of 0.01–0.1 mol %.     

Electrostatic Assembly with Poly(ferrocenylsilanes)

New frontiers in polymer science involve the incorporation of functional species into material systems. The electrostatic layer-by-layer (LBL) self-assembly technique constitutes a versatile tool for nano- and microscale fabrication of devices and novel material structures. Although a rapidly growing attention has been paid to this area, most of the studies conducted were based on organic polymeric electrolytes. Due to synthetic developments, new polymeric structures with inorganic elements and transition metals incorporated in the main chain have become accessible. With the development of new synthesis routes, organometallic poly(ferrocenylsilane) polycations and polyanions emerged. Their charged nature and water-solubility made them excellent candidates for the extension of electrostatic multilayer assembly to organometallic polymeric materials. The present review gives a concise summary on the LBL fabrication of organometallic thin films and microcapsules based on water-soluble poly(ferrocenylsilane) polyions. The unique functions of these structures come from the molecular structure of poly(ferrocenylsilanes), in which silicon atoms and redox-active ferrocene units are present. In this context, the diverse application potentials of these organometallic multilayer structures are also discussed. This article is dedicated to Professor Ian Manners in honor of his great scientific accomplishments, with friendship and sincere respect.     

Spontaneous zwitterionic copolymerisation: An undervalued and efficacious technique for the synthesis of functional degradable oligomers and polymers

The spontaneous zwitterionic copolymerisation (SZWIP) of compatible nucleophilic and electrophilic monomers is a relatively unknown and unexplored method for the synthesis of (predominantly alternating) degradable co- and terpolymers. A wide range of monomers allows for the synthesis of different polymer classes with various functionalities, including poly(aminoester)s, poly(ester amide)s and poly(phosphoester)s. In this review, we discuss this undervalued copolymerisation method and its potential for the facile preparation of functional polymeric systems. In this context, the polymers synthesised to date by SZWIP as well as recent insights into this polymerisation technique are highlighted. Post-polymerisation modifications and applications of polymers obtained by SZWIP are also discussed.     

开环移位聚合制备环烯烃聚合物的新进展

在简要评述环烯烃聚合物的制备方法和各自特点的基础上,针对开环移位聚合反应所涉及的卡宾(Crubbs)催化体系,重点论述了最具前景的Grubbs催化剂的催化机理以及其配体、聚合工艺条件等对聚合过程及产物特性的影响。此外还介绍了开环产物所带有的大量残余双键的加氢过程所需催化剂种类及其特点。     

Catalytic oxidation of alcohols using molecular oxygen mediated by poly(ethylene glycol)-supported nitroxyl radicals

The selective catalytic oxidation of alcohols over a mixture of copper(I) chloride and a number of linear ‘linker-less’ or ‘branched’ poly(ethylene glycol)-supported nitroxyl radicals of the 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) family as a catalyst system has been investigated in the presence of molecular oxygen in a batch reactor. It is found that the activity profile of the polymer-supported nitroxyl radicals is in good agreement with that of low-molecular weight nitroxyl catalysts, for example, allylic and benzylic alcohols are oxidised faster than aliphatic alcohols. The oxidations can be tuned to be highly selective such that aldehydes are the only oxidation products observed in the oxidation of primary alcohols and the oxidations of secondary alcohols yield the corresponding ketones. A strong structural effect of the polymeric nitroxyl species on catalytic activity that is dependent upon their spatial orientation of the nitroxyl radicals is particularly noted. The new soluble macromolecular catalysts can be recovered readily from the reaction mixture by solvent precipitation and filtration. In addition, the recycled catalysts demonstrate a similar selectivity with only a small decrease in activity compared to the fresh catalyst even after five repetitive cycles.     

Studies of cyclic and linear poly(dimethyl siloxanes): 6. Effect of heat

Cyclic and linear poly(dimethyl siloxanes) were heated under vacuum in the temperature range 623–693K for periods of hours or days in the absence of catalysts. The products were analysed by gas-liquid chromatography and gel permeation chromatography. The results for the linear poly(dimethyl siloxanes) were in full agreement with the published work of Thomas and Kendrick. The effect of heat on the cyclic poly(dimethyl siloxanes) was that predicted, assuming that similar siloxane bond interchange reactions take place to those believed to occur in the linear polymers. The cyclic poly(dimethyl siloxanes) produced mixtures of cyclic oligomers, together with polymeric products which have considerably higher molecular weights than the starting materials. It is proposed that these polymeric products consist of mixtures of ring molecules [(CH₃)₂SiO]_x. Some of these cyclic polymers are estimated to contain (on average) more than 10 000 skeletal bonds. Similar mixtures of cyclic oligomers and high molecular weight polymeric products were obtained by heating hexamethylcyclotrisiloxane and octamethylcyclotetrasiloxane.     

Quantitative evaluation of polymeric photosensitizers

Summary The energy transfer ability of free and polymer-bound acetophenone and benzophenone has been studied. The polymeric sensitizers were prepared by acetylation or benzoylation of atactic polystyrene (¯Mn=67.000). Trans-cis isomerization of stilbene, monitored by UV-spectrophotometry, has enabled the energy transfer process to be probed. The values of the Stern-Volmer constants, determined by following this technique, indicate that the energy transfer efficiency of both ketones is higher when they are in free state than when they are polymer-bound.     

Low molecular weight, polymeric, and covalently bound cobalt(II)-phthalocyanines for the oxidation of mercaptans

Cobalt(II)-phthalocyanines in different environments are investigated as catalysts for the oxidation of thiols. Water-soluble low molecular weight 2,9,10,23-tetracarboxyphthalocyanine (1b) and polymeric phthalocyanine (2b) with carboxylic end groups are prepared. Compound1b is covalently bound at linear and cross-linked poly(chloromethylstyrene) in the presence of pyridine to obtain the water-soluble polymers (3a, b) and gel-type polymers (4a, b). Covalent binding of1b to surface modified silica was also realized. Low molecular weight and polymeric phthalocyanines (1a, 2a) are synthesized on silica, alumina, and charcoal. In addition,1a is encapsulated in the interior of NaX zeolite. All materials are efficient catalysts for the oxidation of 2-mercaptoethanol. The mechanism employing water-soluble catalysts is discussed in the direction of a mononuclear complex coordinating dioxygen and thiol. Heterogeneous catalysts containing1a and2a on the carriers show enhanced activity with increasing dispersion. The proposed mechanism considers different reaction sites for the coordination of O₂ and thiol.     

Thermo-responsive Ruthenium Dendrimer-based Catalysts for Hydrogenation of the Aromatic Compounds and Phenols

In this work thermo-responsive ruthenium catalysts, based on the poly(propylene imine) dendrimers cross-linked with the poly(ethylene glycol) diglycidyl ether, have been prepared for the first time. The materials obtained were characterized by X-ray photoelectron spectroscopy and transmission electron microscopy, and tested in the phenol and benzene hydrogenation. Conditions for the metal impregnation into the polymeric matrix were demonstrated to have a great influence both on physical chemical properties of the synthesized catalysts (metal loading, mean particles size, surface structure etc.), and, as a consequence, on their hydrogenation activity and thermo-responsive properties.