Palladium catalysts poly

The coupling reaction of aryl-alkenyl halides with alkenes in the presence of a palladium catalyst and a base is known as the Heck coupling (Scheme 9.4).6 Since the early 1980s, this type of coupling reaction has been used for die syndiesis of poly(arylenevinylene) and related polymers by polymerization of AB- or AA/BB-type of monomers (Scheme 9.5).7... 

At about die same time, die application of the Suzuki coupling, the crosscoupling of boronic acids widi aryl-alkenyl halides in die presence of a base and a catalytic amount of palladium catalyst (Scheme 9.12),16 for step-growth polymerization also appeared. Schliiter et al. reported die synthesis of soluble poly(para-phenylene)s by using the Suzuki coupling condition in 1989 (Scheme 9.13).17 Because aryl-alkenyl boronic acids are readily available and moisture stable, the Suzuki coupling became one of die most commonly used mediods for die synthesis of a variety of polymers.18... 

Further intramolecular reaction of the poly(phenylene)-type polymer leads to more condensed polymers. Tour synthesized polymer 84 bearing a carbonyl moiety and a protected amino group in the phenylene rings by the reaction of boronate 83 and a dibromobenzene monomer. The polymerization takes place in the presence of a palladium catalyst in DME-H2O at 85 °C to give 84 that showed 3/n = 9850-28400 = 1.85-3.70) in 63-97% yields. The resulting polymer 84 is... 

Several supports were studied, including so-called poly-alumazane, which is prepared by subsequent treatment of silanol rich silica with aluminum trichloride and ammonia. With the resulting support palladium catalysts with very high dispersion were obtained. 

HYDROGENATION, CATALYSTS Nickel on alumina. Nickel-Graphite. Palladium-Poly(ethylenimine). Palladium catalysts. Raney nickel. Rhodium catalysts. 

Rod-shaped systems such as 54, extended versions of the widely studied poly(phenylene)s, are available by coupling the para-isomer 45 with a poro-dihaloaromatic unit in the presence of a palladium catalyst [33] (Scheme 13) ... 

Although the selectivity of palladium catalysts in the hydrogenation of 1,5-COD is thus very high, the results also indicate that the hydrogenation of COE to cyclooctane (COA) does not cease after the maximum yield of COE has been attained. Hirai et al. studied the hydrogenation of 1,5-COD over a colloidal palladium catalyst, prepared by reduction of palladium(II) chloride in the presence of poly(iV-vinyl-2-pyrrolidone) in refluxing methanol with addition of sodium hydroxide, in methanol at 30°C and 1 atm H2, and obtained a mixture consisting of 0.4% 1,5-COD, 0.3% 1,4-COD, 97.8%... 

Methyl methacrylate (MMA) is an important commodity since it is polymerized to give poly methylmethacrylate (PMMA), a strong, durable and transparent polymer sold under the trade-names Perspex and Plexiglas. Since the conventional routes to MMA involve either the reaction of acetone with HCN to give the cyanohydrin (which has environmental problems), or the oxidation of isobutene, alternative carbonylation routes to MMA are being developed. One of these is the Lucite Alpha process which is claimed to decrease production costs by ca. 40%. This first synthesizes methyl propionate by a methoxycarbonylation of ethylene (Equation 23), using a palladium catalyst with very high (99.8%) selectivity. In the second step, MMA is formed in 95% selectivity by the reaction of methyl propionate with formaldehyde (Equation 24). 

Enantioselective heterogeneous catalytic hydrogenation using a chiral catalyst was pioneered by Aka-bori and Izumi, who prepared a palladium catalyst supported on silk fibroin. The oxime acetates of diethyl a-ketoglutarate or of ethyl phenylpyruvate were hydrogenated to form glutamic acid (7-15% ee) and phenylalanine (30% Similarly, a palladium-poly-L-leucine catalyst was used for the asym-... 

The semihydrogenation of the carbon-carbon triple bond is a particularly valuable and frequently used application of heterogeneous catalysis to synthetic chemistry, and is the subject of several recent re-views. > Catalysts prepared from palladium and nickel are most commonly used, but the form of the catalyst and the conditions of use affect the results (see Section 3.1.1.2). A polymer-bound palladium catalyst, PdCh with poly-4-diphenylphosphinomethylstyrene, is intended to combine the selective properties of mononuclear transition metal complexes with the ease of separating the product from a solid. Whether catalysts of this type will replace the more traditional heterogeneous catalysts remains to be seen. 

Complete dechlorination of polychlorobenzenes has been accomplished using a palladium catalyst at room temperature and 3-4 atmospheres pressure. 41 The presence of a surfactant also facilitates this reaction. 34, M2 Very good yields of 3,5-dichloroaniline were obtained by the selective hydrodechlorination of poly-chloroanilines over palladium in acidic medium (Eqn. 20.60). 43,M4 Dehydrochlorination of polychlorophenols under these conditions gave good yields of 3,5-dichlorophenol. 44... 

In contrast to polyolefins such as polypropene, polyketones possess true stereo-genic centers along the polymer backbone. Therefore, poly ketones present a unique opportunity to use simple monomers in combination with chiral, enantio-merically pure palladium catalysts to prepare highly isotactic, optically active polymers (or oligomeric compounds) with main-chain chirality. 

Palladium catalyst supported on poly(4-methylstyrene) can be used for biphasic nonpolar Suzuki and Sonogashira coupling of aryl bromides and chlorides with good product yields. The catalyst can be recycled five times with negligible decrease in the activity. 

Hydroalkoxylation of alkynes, or the addition of alcohol to alkynes, is a fundamental reaction in organic chemistry that allows the preparation of enol ethers and a variety of oxygen-containing heterocycles such as furan, pyran, and benzofuran derivatives. Bergbreiter et al. found that a Mnear poly-(A-isopropylacrylamide) (PNIPAM) polymer exhibited inverse temperature solubility in water (i.e., soluble in cold water but insoluble in hot water). A recoverable homogeneous palladium catalyst was prepared based on the polymer. The PNIPAM-bound Pd(0) catalyst was effective for the reaction of 2-iodophenol with phenylacetylene in aqueous THE media to give the target product... 

Using a quite different approach, polymeric beads of supported ionic liquid palladium catalysts comprised of polymerized ionic liquid monomers and palladium complexes have been synthesized using traditional suspension polymerization methods [86]. Here, polymeric ionic liquid beads were made from polymerization of l-butyl-3-vinylimidazolium bis(trifluoromethyl sulfonyl)imide and poly(vinylalcohol) by heating with AlBN (2,2 -azobis(2-methylpropionitrile)) in the presence of l,l -bis[l,8-octyl)-3-vinylimidazolium bis(trifluoromethyl sulfonyl)imide as cross-linker (Scheme 5.6-6). The ionic liquid support beads proved to be thermally stable up 250 °C which is significantly higher than conventional vinyl resins. 

HYDROGENATION OF ALKADIENES AND POLY-ENES 385 TABLE 8.10. Comparison of Calculated and Observed Product Selectivities in the Hydrogenation of 1,3-Pentadiene on Palladium Catalysts ... 

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