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Journal ArticleDOI

Transition metal ions supported on hydrogels as hydrogenation catalysts

01 Jun 1990-Journal of Molecular Catalysis (Elsevier)-Vol. 60, Iss: 2, pp 189-207

AbstractSynthesis of new hydrogel polymers based on 2-hydroxyethyl methacrylate and other functional monomers is described. These copolymers are useful for anchoring palladium and rhodium species. The resulting supported catalysts are effective for the hydrogenation of alkenes, alkynes and dienes under mild conditions. The supported catalysts have been characterised by chemical analysis, particle size measurements, IR, TGA and X-ray photoelectron spectra. Kinetics of hydrogenation have been evaluated using the concepts applicable to slurry reactors. The hydrogenation proceed through the ‘unsaturate route’. Relative reactivities of a few substrates, solvent and particle size effects and selectivities by product analysis have been assessed. These catalysts possess excellent recycling efficiencies.

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Citations
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Journal ArticleDOI
Abstract: The synthesis and use of nitrogen-containing copolymers for anchoring Ru(II) and Rh(I) species is described. The supported species are effective as catalysts for the decomposition of H 2 O 2 in aqueous medium at neutral pH. The polymers as well as the supported catalysts have been characterised by physical and chemical methods. The effects of [H 2 O 2 ], catalyst loading and pH of the medium on the rate of decomposition have been studied. Suitable mechanisms have been proposed to account for the kinetics. Recycling efficiencies of the catalysts are found to be good.

15 citations

Journal ArticleDOI
Abstract: Kinetic Investigations of the Hydrogenation of Ligands in Catalyst Precursors for Asymmetric Reduction of Prochiral Olefines1 The comparison of chiral rhodium(I) complex catalysts of the type [Rh(L)PP*]A (L = cyclic diolefin; PP* = chiral bis(phosphane) and A = anion like BF) regarding their hydrogenating activity against prochiral substrates is hampered by the induction period in the hydrogen consumption which can be attributed to the formation of the catalytically active species from the diolefin precatalyst. The competing hydrogenation of diolefin [e.g. cis,cis-cycloocta-1,5-diene (COD), norborna-2,5-diene (NBD)] and prochiral substrate may cause a maximum of the hydrogenation rate, which is characteristic for different catalyst/substrate/solvent systems. Michaelis-Menten rate constants for the hydrogenation of COD and NBD were determined for different chiral catalysts by stoichiometric and catalytic hydrogenations. The rate constants differ for one selected diolefin up to a factor of 40. The hydrogenation of NBD is generally 5–8 times faster than the COD hydrogenation. In the special case of precatalysts based on he-xopyranoside bis(phosphinites) the rate constants for the NBD hydrogenation in comparison with those for COD are higher up to a factor of 48. In some cases the hydrogenation of the mono-ene is faster than that of the diolefin (e.g. COD, NBD). The high hydrogenation rate reported in the literature for some precatalysts in the asymmetric hydrogenation of prochiral olefins is caused in part by the relatively fast diolefin hydrogenation which facilitates the complete formation of the catalyst. The influence of substrate, solvent, and some experimental conditions on the induction period will be discussed.

13 citations

Book ChapterDOI
01 Jan 1994
Abstract: The subject of supported metal complexes as catalysts was reviewed by Hartley in a book published in 1985 [1], and hydrogenation was extensively treated. Supported metal complexes as hydrogenation catalysts were also reviewed by Yermakov and Arzamaskova in 1986 [2], and enantioselective versions of the reaction by Hetflejs in the same year [3]. Therefore account will focus on work published since 1984.

12 citations

Journal ArticleDOI
Abstract: A polymer-supported palladium-imidazole catalyst was used to catalyze the hydrogenation of various olefins under mild conditions. The rate of hydrogenation was studied. The effects of factors such as substrate concentration, catalyst concentration, partial pressure of hydrogen and temperature on initial rate of reaction of selected olefins were investigated. A mechanism for the reaction was proposed from the rate equation. The effects of the solvent and structure of the olefin on the rate of hydrogenation were investigated. The catalyst showed good reusability without any leaching of metal from the support. The homologous analog of the polymer-supported catalyst could not be used as catalyst for the hydrogenation of olefins in methanol because there was precipitation of the metal during reaction.

8 citations


References
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Journal ArticleDOI
Abstract: A polymer-bound palladium (II) chloride complex has been prepared by the reaction of palladium chloride with a phosphinated polystyrene. Under mild conditions the polymer palladium complex catalyzes the hydrogenation of alkenes and alkynes, particularly the selective hydrogenation of conjugated dienes to monoenes. The catalytic activity for a variety of substrates decreases in the following order: conjugated dienes > nonconjugated dienes > terminal olefins > internal olefins. Oxygen-containing solvents remarkably promote the catalytic activity of the palladium complex. The rates of hydrogenation of cyclohexene, styrene, and 1,3-cyclooctadiene have been studied and the dependence on factors such as substrate concentration, catalyst concentration, pressure, and temperature has been determined. The data can be accommodated by rate expressions of the form: rate = k1k2[S][H2][A](k−1 + k1[S] + k2[H2] for cyclohexene, and rate = k2[H2][A] for styrene and 1,3-cyclooctadiene, where [S] and [A] are the olefin and catalyst concentrations, respectively, and [H2] is the concentration of hydrogen in solution. A mechanism for hydrogenation is proposed on the basis of the kinetic studies. It is revealed that the reactivities of the polymer palladium complex catalyst and of an analogous catalyst system PdCl2(PPh3)2SnCl2 reflect the electronic state and the coordination number of the complexes.

71 citations

Journal ArticleDOI
Abstract: Poly(styryl)bipyridine, 1, is produced from the reaction of lithiated polystyrene with bipyridine in tetrahydrofuran. Under our conditions, bipyridine becomes bound to 1615% of the phenyl residues. The reaction of 1 with a variety of transition-metal salts can be carried out in a variety of swelling solvents and results in formation of polymer-bound bipyridine transition-metal complexes. The extent of metal incorporation depends on solvent, metal ion concentration, and the identity of the metal species. Zerovalent metal complexes such as@-Ph-bpy-M(CO), (M = Cr, Mo, W) are readily prepared from the reaction of 1 with the metal hexacarbonyl complexes. (Poly(styry1)bipyridyl)palladium acetate is an active catalyst for the hydrogenation of olefins at ambient pressure and temperature. It can also be used to catalyze the acetoxylation of benzene; however, the percent conversion in this case is rather low.

49 citations

Journal ArticleDOI
Abstract: Semihydrogenations of 15 acetylenes to olefins catalyzed by polymer-bound palladium(II) complexes have been studied synthetically and mechanistically, and the hydrogenation of phenylacetylene has been studied kinetically. In the hydrogenation of isolated acetylenes, the catalyst generated corresponding olefins in high selectivities (above 92%). In the case of conjugated acetylenes, the catalyst generated corresponding conjugated olefins in relatively low selectivities (71–85%), whereas phenylacetylene was hydrogenated to styrene in a high selectivity (93%). A high activity of the catalyst was observed in oxygen-containing solvents such as dimethylformamide, tetrahydrofuran, dimethyl sulfoxide, and ethanol. The catalytic activity is affected more strongly by the π-acidity of acetylenes than their steric factor. The hydrogenation rate of phenylacetylene is expressed by the form: R = k2[H2][A], where [H2] and [A] are hydrogen and the catalyst concentrations, respectively. A mechanism for the hydrogenation is proposed on the basis of kinetic studies. Finally, it is summarily discussed what factors control the activity and the selectivity of the polymer catalyst for the hydrogenation of carbon-carbon double and triple bonds. This polymer-bound palladium complex was shown to be comparable in selectivity to cationic rhodium and the Lindlar catalysts.

32 citations