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Journal ArticleDOI

Polymer-supported palladium and rhodium species as hydrogenation catalysts

15 Jan 1997-Journal of Polymer Science Part A (Wiley)-Vol. 35, Iss: 1, pp 105-122
Abstract: The synthesis of new copolymers containing amino and heterocyclic ligands and their use for anchoring Pd and Rh species is described. The supported catalysts are effective for the hydrogenation of alkenes, dienes, alkynes, and nitrobenzene under very mild conditions. The catalysts have been characterized by chemical analysis, particle size measurement, IR, and x-ray photoelectron spectroscopy. Relative reactivities and the effects of substrate structure, solvents, catalyst loading, anchoring ligands, metal species, and particle size on the rates of hydrogenation have been determined using a wide variety of substrates. The kinetics of hydrogenation have been analyzed using concepts suitable under slurry reaction conditions. Comparisons between different oxidation states of the same metal and between different metal species have also been made. The recycling efficiencies of the catalysts have been determined and found to be very good. © 1997 John Wiley & Sons, Inc. more

Topics: Catalyst support (57%), Catalysis (56%), Rhodium (56%) more
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Journal ArticleDOI
Victor Chechik1, Richard M. Crooks1Institutions (1)
Abstract: Here we describe the application of dendrimer-encapsulated Pd nanoparticles to fluorous biphasic catalysis. 1 Complexation of Pd/dendrimer composites with perfluorinated carboxylic acids renders the resulting nanocomposites preferentially soluble in fluorinated hydrocarbons. These new catalysts show high activity and selectivity for biphasic hydrogenation of alkenes and conjugated dienes. Moreover, the catalysts can easily be recovered and used for multiple reactions. Reactions in biphasic fluorous/organic systems were suggested by Horvath and Rabai in 1994 2 to facilitate recovery and recycling of soluble catalysts. The general approach to biphasic catalysis is illustrated in Scheme 1. 3 The system consists of organic and fluorous layers. The catalyst is selectively soluble in the fluorous phase, while the reactants are preferentially soluble in the organic solvent. Stirring, sonicating, and/or heating of the mixture leads to formation of a fine emulsion and partial homogenization (with some solvents, complete homogenization is obtained at elevated temperatures), and the catalytic reaction proceeds at the interface between the two liquids. When the reaction is over, the liquid phases are separated, the product is isolated from the organic phase, and the catalyst-containing fluorous layer is recycled. Such easy separation and recycling are particularly attractive in terms of “green chemistry”, and a number of fluorous phase-soluble catalysts have been reported in the literature, including some based on metal complexes. 4,5 Preparation of fluorous phase-soluble metal nanoparticles, however, has not previously been reported. Catalytic properties of metal nanoparticles have been explored since the pioneering studies of Rampino and Nord in the early 1940s. 6 Over the past decade research in this area intensified, 7 more

226 citations

Book ChapterDOI
Richard M. Crooks1, Buford I. Lemon1, Li Sun1, Lee K. Yeung1  +1 moreInstitutions (1)
01 Jan 2001-
TL;DR: This chapter describes composite materials composed of dendrimers and metals or semiconductors, which are useful for a range of catalytic applications including hydrogenations and Heck chemistry. more

Abstract: This chapter describes composite materials composed of dendrimers and metals or semiconductors. Three types of dendrimer/metal-ion composites are discussed: dendrimers containing structural metal ions, nonstructural exterior metal ions, and nonstructural interior metal ions. Nonstructural interior metal ions can be reduced to yield dendrimer-encapsulated metal and semiconductor nanoparticles. These materials are the principal focus of this chapter. Poly(amidoamine) (PAMAM) and poly(propylene imine) dendrimers, which are the two commercially available families of dendrimers, are in many cases monodisperse in size. Accordingly, they have a generation-dependent number of interior tertiary amines. These are able to complex a range of metal ions including Cu2+, Pd2+, and Pt2+. The maximum number of metal ions that can be sorbed within the dendrimer interior depends on the metal ion, the dendrimer type, and the dendrimer generation. For example, a generation six PAMAM dendrimer can contain up to 64 Cu2+ ions. Nonstructural interior ions can be chemically reduced to yield dendrimer-encapsulated metal nanoparticles. Because each dendrimer contains a specific number of ions, the resulting metal nanoparticles are in many cases of nearly monodisperse size. Nanoparticles within dendrimers are stabilized by the dendrimer framework; that is, the dendrimer first acts as a molecular template to prepare the metal nanoparticles and then as a stabilizer to prevent agglomeration. These composites are useful for a range of catalytic applications including hydrogenations and Heck chemistry. The unique properties of the interior dendrimer microenvironment can result in formation of products not observed in the absence of the dendrimer. Moreover the exterior dendrimer branches act as a selective gate that controls access to the interior nanoparticle, which results in selective catalysis. In addition to single-metal nanoparticles, it is also possible to prepare bimetallic nanoclusters and dendrimer-encapsulated semiconductor nanoparticles, such as CdS, using this same general approach. more

196 citations

Journal ArticleDOI
Abstract: Composite colloids of gold and polypyrrole were prepared using two different methods: 1, using pyrrole colloid, created by the oxidation of pyrrole by ferric chloride, to subsequently reduce chlorauric acid and, 2, oxidizing pyrrole monomer with chlorauric acid in a sodium dodecylbenzene sulfonate solution. In each case, the polypyrrole colloid consisted of irregularly shaped particles approximately 500 nm in diameter. The gold produced in each case was in the form of irregular spheres, approximately 407 nm in diameter in method 1 and 13 nm in method 2. X-ray photoelectron spectroscopy was used to determine the oxidation state of the species present. Transmission electron microscopy and light scattering data were used to determine the particle sizes of both gold and polypyrrole colloids. Energy dispersed spectrum X-ray analysis and electron diffraction were used to confirm the presence of metallic gold in the composite colloids. The second-order rate constant for the reaction of chlorauric acid with pyrrole in dilute solution was found to he 13 M -1 s -1 . Aqueous solutions of palladium, platinum, rhodium, cobalt, tin, silver, zinc, nickel, titanium, cadmium, mercury, arsenic, and selenium were also examined for their potential to act as oxidants to produce composite polypyrrole colloids. Palladium, platinum, and rhodium salts were suitable oxidants, producing polypyrrole in less than 12 h. more

194 citations

Journal ArticleDOI
Ryo Akiyama1, Shu Kobayashi1Institutions (1)
11 Feb 2009-Chemical Reviews
TL;DR: The chiral stationary phase for high-performance liquid chromatography showed good chiral recognition ability towards various racemates, including Cu(acac)2, but not as well as in the phase for low-performance materials like Palladium. more

Abstract: 2.6. Microencapsulated Cu(acac)2 [MC Cu(acac)2] 606 2.7. Microencapsulated Palladium [MC Pd] 607 2.8. Microencapsulated Methathesis Catalyst 609 3. Polymer Incarcerated Catalysts 611 3.1. Polymer Incarcerated Palladium [PI Pd] 611 3.2. Polymer-Micelle Incarcerated (PMI) Palladium 617 3.3. Polymer Incarcerated Ruthenium Catalyst 619 3.4. Polymer-Micelle Incarcerated Scandium Trifluoromethanesulfonate [PMI Sc(OTf)3] and Ruthenium Catalyst [PMI Ru] 621 more

189 citations

Journal ArticleDOI
Shu Kobayashi1, Ryo Akiyama1Institutions (1)
TL;DR: It is noted that this method enables direct immobilization of metals onto polymers, and that normally unstable species such as Pd(0)(PPh3) can be kept stable by this immobilization technique, and it is expected that other metal catalysts can be immobilized using this microencapsulation technique. more

Abstract: Immobilized catalysts have been reinvestigated from two aspects; as keys to environmentally benign chemical processes and high-throughput organic synthesis for combinatorial chemistry. While most known polymer-supported catalysts are less active than the corresponding original catalysts, new types of polymer-supported catalysts, microencapsulated catalysts, have been developed. The catalysts were immobilized on to polymers using physical envelopment by polymer backbones and interaction between π electrons of benzene rings of the polystyrenes used as polymer backbones and vacant orbitals of the catalysts. Microencapsulated Sc, Os, Pd and Ru catalysts have been successfully prepared and high activities have been attained. In all cases, no leaching of the catalysts occurred, and the immobilized catalysts were recovered quantitatively by simple filtration and reused without loss of activity. It is noted that this method enables direct immobilization of metals onto polymers, and that normally unstable species such as Pd(0)(PPh3) can be kept stable by this immobilization technique. It is expected that other metal catalysts can be immobilized using this microencapsulation technique. more

148 citations

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