Polymer-supported Catalysts Research Articles

Polymer-supported half-titanocene catalysts for the syndiospecific polymerization of styrene

Monocyclopendienyltitanium trichloride (CpTiCl 3 ) was supported on polymer carriers with different hydroxyl contents, and the supported catalysts were used for styrene polymerization. The supported catalysts exhibited high activity even at low Al/Ti ratios and increased the molecular weight of the products, indicating that polymer carriers could stabilize the active sites. The polymers prepared with unsupported and supported catalysts were extracted with boiling n-butanone and characterized by carbon nuclear magnetic resonance ( 13 C NMR) and differential scanning calorimetry. The polymers obtained by supported catalysts had a high fraction of boiling n-butanone-insoluble part and high melting temperatures, but 13 C NMR results showed that syndiotacticity decreased compared with that of polymers prepared with an unsupported catalyst. ESR study on the supported catalysts confirmed that the active sites supported on the carrier dropped into the solution and formed active sites the same as those in the unsupported system when they reacted with methylaluminoxane. 13 C NMR analysis showed that the polymerization mechanism of the supported active sites was an active-site controlled mechanism instead of a chain-end controlled mechanism of the unsupported active sites.

Novel type of heterogenized CuCl2 catalytic systems for oxidative carbonylation of methanol

A novel type of heterogenized CuCl2 catalysts was designed for the oxidative carbonylation of methanol to dimethyl carbonate (DMC) taking account of the plausible reaction mechanism and intermediates. To prevent severe corrosion of the reaction equipment materials due to Cl− while keeping the catalytic activity of the homogeneous CuCl2 catalyst, we adopted, as supports (or ligands) of CuCl2, four polymers, bearing a 2,2′-bipyridine (bpy) or pyridine (py) unit, namely, poly(2,2′-bipyridine-5,5′-diyl) (Pbpy), poly(pyridine-2,5-diyl) (Ppy), poly(N,N′-bisphenylene-2,2′-bipyridine-4,4′-dicarboxylic amide) (Bpya), and poly(4-methyl-4′-vinyl-2,2′-bipyridine) (Pvbpy), together with one chelate compound, 8-quinolinol. The catalytic activity, stability of heterogenized CuCl2 and their corrosivities to stainless steels were examined in the liquid-phase reaction of the oxidative carbonylation of methanol. These polymer-supported catalysts showed considerable catalytic activity and stability for the DMC synthesis. In particular, the Pbpy-CuCl2 and Ppy-CuCl2 catalysts exhibited high DMC yields and selectivity comparable to those of the homogeneous CuCl2 catalyst. This high activity appears to be associated with the presence of the π-conjugated system in the polymers, which affect the redox reactions of Cu involved in the catalytic reaction. All of the polymer-supported CuCl2 catalysts could be easily recycled after filtration, and the initial catalytic activity was maintained after three times of use. The corrosive characters of the catalysts were closely related to CuCl2 leaching from the supports, which reflects the ability of supports to coordinate Cu. These experimental results suggest that both the electronic structure and the coordination ability of the polymer supports are key factors for the development of an effective catalytic system.

Functionalized polystyrene as a versatile support for olefin polymerization catalysts

Heterogeneous polyolefin catalysts based on metallocenium salts of weakly coordinating anions can be prepared via a series of simple reactions from lightly crosslinked chloromethylated polystyrene beads. Catalytic sites are distributed homogeneously throughout the polystyrene particles. The nonporous nature of these catalysts affords a high degree of control over the olefin uptake rate, avoiding problems of premature catalyst fragmentation that often plague high-surface-area heterogeneous catalysts based on highly reactive species. The choice of amine as the means of binding or templating allows catalysts based on a wide variety of metallocenes to be readily prepared by the same synthetic approach. The dative interactions between the metallocene cation and the amine functionality of the support material are sufficient to prevent extraction under polymerization conditions to yield excellent particle morphology of the polyolefin product, but they are not so strong as to affect the nature of the polyolefin produced. The polymer-supported catalysts have been used effectively for the polymerization of ethylene and polypropylene. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2979–2992, 2000

Synthesis of porous supports containingN-(p-hydroxyphenyl)- orN-(3-4-dihydroxybenzyl) maleimide-anchored titanates and application as catalysts for transesterification and epoxidation reactions

N-(p-acetoxyphenyl)maleimide and N-(piperonyl)maleimide were polymerized in suspension to give macroporous supports. After deprotection of the p-acetoxyphenyl and of the piperonyl groups, resins with pendant p-hydroxyphenyl and catechol units were obtained. These results illustrate a very easy and convenient way to synthesize phenol and catechol containing supports. Polymer-supported transesterification and epoxidation catalysts were obtained by immobilization of Ti(OiPr)4 and TiCl4. These catalysts were efficient for both reactions and could be recycled several times although some titanium leaching (≤ 20%) was observed in each case. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2879–2886, 2000

Novel polymer-supported β-dithioketonate nickel catalysts for selective propylene dimerization

Brominated and chloromethylated styrene–divinylbenzene resins were used for the synthesis of polymer-bound dithio-β-diketones, obtained by anchoring the chelate ligand through the central position. The heterogenized dithio-β-diketone ligand was subsequently reacted either as sodium salt with a Ni(II) phosphino derivative or directly with a Ni(0) complex in the presence of a free phosphine and activated in situ with an aluminum co-catalyst for the selective dimerization of propylene to 2,3-dimethylbutenes. The hetetogenized catalysts so obtained showed, particulary when prepared starting from chloromethylated styrene/divinylbenzene resins, very high activity and selectivity towards 2,3-dimethylbutenes. Moreover, the above catalysts, at least under the adopted reaction conditions, did not display any appreciable metal leaching during the catalytic cycle, thus working as really heterogeneous systems. Copyright © 1999 John Wiley & Sons, Ltd.

New polymer-supported catalysts derived from Cinchona alkaloids: Their use in the asymmetric Michael reaction

New polymer-supported catalysts derived from quinine and quinidine were elaborated and tested in the conjugate addition between enamino ester 13 and methyl vinyl ketone. By employing a 7-atom-length spacer, an excellent enantioselectivity was observed (87%).

Asymmetric Hydroformylation of Olefins in Highly Crosslinked Polymer Matrixes

Abstract When polymer-immobilized chiral phosphine-phosphite–Rh(I) complexes were used, the asymmetric hydroformylation of styrene gave 2- and 3-phenylpropanals with a substrate/catalyst ratio of 2000, iso/normal ratios of 84/16 to 89/11, and 89% R enantiomeric excess of 2-phenylpropanal; these results were at the highest level in catalytic activity, regio-, and enantioselectivities. Recovery-reuse of the catalyst was examined. Asymmetric hydroformylation of vinyl acetate, (Z)-2-butene, and 3,3,3-trifluoropropene was also successfully performed with the polymer-supported catalysts.

Highly Effective Soluble Polymer-Supported Catalysts for Asymmetric Hydrogenation

Highly Effective Soluble Polymer-Supported Catalysts for Asymmetric Hydrogenation

Polymer‐supported zirconocene catalyst for ethylene polymerization

The use of crosslinked poly(styrene-co-4-vinylpyridine) having functional groups as the support for zirconocene catalysts in ethylene polymerization was studied. Several factors affecting the activity of the catalysts were examined. Conditions like time, temperature, Al/N (molar ratio), Al/Zr (molar ratio), and the mode of feeding were found having no significant influence on the activity of the catalysts, while the state of the supports had a great effect on the catalytic behavior. The activity of the catalysts sharply increased with either the degree of crosslinking or the content of 4-vinylpyridine in the support. Via aluminum compounds, AlR3 or methylaluminoxane (MAO), zirconocene was attached on the surface of the support. IR spectra showed an intensified and shifted absorption bands of CN in the pyridine ring, and a new absorption band appeared at about 730 cm−1 indicating a stable bond AlN formed in the polymer-supported catalysts. The formation of cationic active centers was hypothesized and the performance of the polymer-supported zirconocene was discussed as well. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 37–46, 1999

Polymer-supported zirconocene catalyst for ethylene polymerization

The use of crosslinked poly(styrene-co-4-vinylpyridine) having functional groups as the support for zirconocene catalysts in ethylene polymerization was studied. Several factors affecting the activity of the catalysts were examined. Conditions like time, temperature, Al/N (molar ratio), Al/Zr (molar ratio), and the mode of feeding were found having no significant influence on the activity of the catalysts, while the state of the supports had a great effect on the catalytic behavior. The activity of the catalysts sharply increased with either the degree of crosslinking or the content of 4-vinylpyridine in the support. Via aluminum compounds, AlR3 or methylaluminoxane (MAO), zirconocene was attached on the surface of the support. IR spectra showed an intensified and shifted absorption bands of CN in the pyridine ring, and a new absorption band appeared at about 730 cm−1 indicating a stable bond AlN formed in the polymer-supported catalysts. The formation of cationic active centers was hypothesized and the performance of the polymer-supported zirconocene was discussed as well. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 37–46, 1999

Liquid-phase chemistry: recent advances in soluble polymer-supported catalysts, reagents and synthesis

Chemistry on soluble polymer-matrices, termed liquid-phase organic synthesis, is emerging as a viable alternative or adjunct to the classical solid-phase approach across the broad spectrum of polymer-supported organic chemistry. This review details the significant advances in liquid-phase synthetic methodologies, reagents, catalysts and supports that have appeared from 1997 to the present.

Poly(4-Vinylpyridinium P-Toluenesulfonate) as a Polymer-Supported Catalyst for Hydrolysis of Tetrahydropyranyl Ethers

Poly(4-vinylpyridinium) p-toluenesulfonate is used as an immobilized catalyst for the hydrolysis of tetrahydropyranyl ethers. This method is mild, efficient and convenient, giving the corresponding products in good to excellent yields and purity.

Reusable polymer-supported palladium catalysts: An alternative to tetrakis(triphenylphosphine)palladium in the Suzuki cross-coupling reaction

The Suzuki cross-coupling reaction of a boronic acid and a bromoaromatic compound requires palladium catalysis. Almost identical yields were obtained in the usual conditions, with 30 mequiv. of Pd(PPh 3) 4, and with 2 mequiv of a polymer-supported catalyst, which was easily prepared in two steps from Merrifield polymer. Recovery and reuse of the catalyst is easy, and only 0.60% of the initial amount of palladium is most during a reaction.

Polymer-supported catalysts for efficient on-column preparation of 2-deoxy-2-[ 18F]fluoro-D-glucose

Several kinds of polymer-supported quaternary salts, such as dimethylaminopyridinium or tributylphosphonium salts, have been examined for the on-column preparation of [ 18F]FDG. Factors affecting [ 18F]fluoride trapping efficiency and [ 18F]fluorination yield have been optimized. [ 18F]Fluoride was practically, quantitatively trapped from flowing water and the subsequent 18F-substitution was carried out on-column with a radiochemical yield of over 70% (EOB). The improvement in the [ 18F]fluorination yield was achieved by introducing a spacer alkene chain between the supporting resin molecule and the catalytic site. A resin with higher cross-linkage and lower content of catalytic sites was shown to be useful for preventing column plugging.

Novel polymer-supported β-diketonate nickel catalysts for α-olefin activation

Styrene–divinylbenzene resins were used for the synthesis of different polymer-bound β-diketones, obtained by anchoring the chelating group through either the central or the lateral position. The heterogenized diketone ligand was subsequently reacted with Ni(COD)2 analogously to the corresponding homogeneous catalysts active in α-olefin oligomerization. The heterogenized catalysts showed a good activity only when the central position of the chelate moiety was free. Heterogenization caused a significant change of selectivity: olefin oligomerization was accompanied by the formation of a large amount of polymeric products. This behavior is discussed in terms of steric effects caused by the bulky polymeric ligand. © 1998 John Wiley & Sons, Ltd.

Polymer-supported phase-transfer catalysts: synthesis and high catalytic activity of ammonium and phosphonium salts bound to linear and crosslinked poly(glycidyl methacrylate)

The synthesis of polymer-supported phase-transfer catalysts is described by the polymerization of glycidyl methacrylate (PGMA), either linear or crosslinked. The PGMA polymers were hydrolysed and later modified with chloroacetyl chloride. The chloroacetylated polymers were treated with either triphenylphosphine or triethylamine to produce polymer-supported phosphonium or ammonium salts. The catalytic behavior of the prepared catalysts was tested for some nucleophilic substitution reactions such as thiocyanation, cyanation, and nitration of benzyl bromide as model reactions.

Thermal Stability of a Polymer-Supported Rhodium Catalyst for Methanol Carbonylation

A novel rhodium-containing diphenylphosphinate copolymer of styrene ad divinylbenzene (used as catalyst for methanol carbonylation) was prepared and studied by means of thermoanalytical methods. Simultaneous TG-DTA experiments were run to assess the effect of the grafting procedure on the thermal behaviour. Additional information concerning the structural modifications observed was obtained by infrared spectroscopy.

Hydrogenation of olefins over palladium(II) complexes supported on a modified macroporous polymer bead

Gellular and macroporous polymer supports have been prepared. A modified polymer support has also been prepared by coating the internal pore wall of macroporous poly(styrene-co-divinylbenzene) with lightly crosslinked polymer containing functional groups. The supports were phosphinated and PdCl 2 was supported on them. The supports and catalysts were characterized using scanning electron microscopy and Fourier transform infrared spectroscopy. The polymer-supported Pd catalysts were used in the hydrogenation of olefins. The effects of the support structure and solvent were also studied.

Polymer-Supported Quinuclidinyl Catalysts for Synthesis of Cyclopolymerizable Monomers via the Aldehyde−Acrylate Coupling Reaction

With an appropriate amine catalyst, formaldehyde addition to acrylates results in α-hydroxymethyl acrylate intermediates that undergo a further condensation reaction to provide ether-linked 1,6-diene monomers capable of efficient cyclopolymerization. While 1,4-diazabicyclo[2.2.2]octane (DABCO) is an effective catalyst in the synthesis of these cyclopolymerizable monomers, a series of polymer-supported amine catalysts were prepared and evaluated in an effort to further simplify this process. 3-Quinuclidinol was reacted with methacrylic anhydride to give the functionalized methacrylate monomer, which was copolymerized with methyl methacrylate and triethylene glycol dimethacrylate. Various polymerization techniques (bulk, solution, and suspension) were used to produce the cross-linked polymeric catalysts. Supports with mole fractions of catalyst ranging from 20% to 98% were examined. In reactions with ethyl acrylate and paraformaldehyde, certain polymer-supported catalysts gave near quantitative conversion t...

The Polymer Effect on Catalysts. Aldimine-Selective Reactions in the Coexistence of Aldehydes Using a Polymer-Supported Scandium Catalyst

The Polymer Effect on Catalysts. Aldimine-Selective Reactions in the Coexistence of Aldehydes Using a Polymer-Supported Scandium Catalyst