Dendritic effect in polymer-supported catalysis of the intramolecular Pauson–Khand reaction

Dahan, Adi; Portnoy, Moshe

doi:10.1039/b207625j

Cited by 58 publications

(24 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…65 Both 4-and 2-diphenylphsphinobenzoate-bearing dendritic resins (generations 0 -3) were complexed with Co 2 (CO) 8 according to a literature procedure, 66 and the formed systems were tested in the intramolecular reaction of 1,6-enyne (Scheme 24). 53 Along with the regular Pauson-Khand cyclopentenone product, an Alder-ene byproduct was obtained in all experiments. The 4-diphenylphosphinobezoate series of catalysts showed a remarkable increase (greater than twofold) in the yield of the Pauson-Khand product as a function of the dendron generation (Table 7).…”

Section: Pauson-khand Reactionmentioning

confidence: 80%

“…Thus, we observed reduced rates of alcohol esterification for higher generations. 53 Bradley's group demonstrated reduced rates of Fmoc release from dendron-bound Fmoc-protected amines. 38 The Fmoc release rate was generation-dependent but was also influenced by the structure of the dendron molecules.…”

Section: Properties Of the Dendronized Supportsmentioning

confidence: 99%

“…12). 49,53,61 Thus, it is not solely the length of the spacer that matters: the average distance between the attachment site on the polymer core and the catalytic unit probably matters as well. This average distance for a given core and catalytic unit will be dictated by the spacer length but even more so by the architecture and arrangement in three-dimensional space.…”

Section: Possible Reasons For the Effectsmentioning

confidence: 99%

See 2 more Smart Citations

Dendrons and dendritic catalysts immobilized on solid support: Synthesis and dendritic effects in catalysis

Dahan

Portnoy

2004

J. Polym. Sci. A Polym. Chem.

Self Cite

View full text Add to dashboard Cite

Dendrimers, the aesthetically beautiful macromolecules displaying a variety of potentially useful architecture-induced properties, are traditionally assembled in solution. However, since 1988, a number of dendritic structures have been assembled on insoluble organic and inorganic polymers, and thus dendronized supports have been formed. One of the major applications of these new materials is in the field of heterogeneous catalysis. Supported dendritic catalytic systems, bearing the catalytic units on the dendron periphery, have been examined in the last 5 years in such reactions as hydroformylation, Heck and other Pd-catalyzed COC bond formations, oxidation, and enantioselective addition to aldehydes. In the majority of these studies, substantial dendritic effects on the reactivity, selectivity, or recyclability of the catalysts were observed. Although a number of factors have been suggested as sources of the effects, it is most likely that the phenomenon has a multicomponent origin. Additional research, including a full determination of the effects and their causes, is likely to lead to markedly better heterogeneous catalytic systems.

show abstract

Section: Pauson-khand Reactionmentioning

confidence: 80%

Section: Properties Of the Dendronized Supportsmentioning

confidence: 99%

Section: Possible Reasons For the Effectsmentioning

confidence: 99%

See 1 more Smart Citation

Dendrons and dendritic catalysts immobilized on solid support: Synthesis and dendritic effects in catalysis

Dahan

Portnoy

2004

J. Polym. Sci. A Polym. Chem.

Self Cite

View full text Add to dashboard Cite

show abstract

“…One or more CO can be substituted by phosphines, and these can be immobilized in resins thus giving anchored cobalt complexes (27), that were able to catalyze the reaction of 28 giving 29 with good yield and minor amounts of 30 (Scheme 10) [76]. Other cobalt metal clusters like Co 4 (CO) 12 [77] or methylidynetricobalt nonacarbonyl [78] have exhibited high reactivity in the catalytic PKR.…”

Section: Catalytic Pkrmentioning

confidence: 99%

Cascade Reactions Involving Pauson—Khand and Related Processes

Pérez‐Castells

2006

ChemInform

View full text Add to dashboard Cite

show abstract

“…Additionally, we aimed to shorten the time for dendrimer recycling, as traditional dendrimer mediated syntheses require 24 h of dialysis with multiple solvent changes. Thus, our motivation for this work was to develop air and water free synthetic routes and to facilitate rapid recycling of the dendrimer by eliminating the need for dialysis.Several research groups have attempted to grow or build low generation dendritic polymers on silica, 20-25 polystyrene, [26][27][28] and various resins 29,30 for the purpose of immobilizing catalysts onto solid supports. [31][32][33] One particular study investigated Pd NP catalysts templated on hyperbranched polymers constructed on mesoporous silica.…”

mentioning

confidence: 99%

Air and Water Free Solid-Phase Synthesis of Thiol Stabilized Au Nanoparticles with Anchored, Recyclable Dendrimer Templates

et al. 2007

View full text Add to dashboard Cite

Solid-phase synthetic templates for Au nanoparticles were developed using Merrifield resins and polyamidoamine (PAMAM) dendrimers. This synthetic scheme affords the opportunity to prepare metal nanoparticles in the absence of air and water, and it does not necessitate phase transfer agents that can be difficult to remove in subsequent steps. Amine-terminated generation 5 PAMAM (G5NH 2 ) dendrimers were grafted to anhydride functionalized polystyrene resin beads and alkylated with 1,2-epoxydodecane to produce G5C12 anch . The anchored dendrimers bound both Co II and Au III salts from toluene solutions at ratios comparable to those of solution phase alkyl-terminated PAMAM dendrimers. The encapsulated Au III salts could be reduced with NaBH 4 to produce anchored dendrimer encapsulated nanoparticles (DENs). Treatment of the anchored DENs with decanethiol in toluene extracted the Au nanoparticles from the dendrimers as monolayer protected clusters (MPCs). After a brief NaCN etch, the anchored dendrimers were readily recycled and a subsequent synthesis of decanethiol Au MPCs was performed with comparable MPC yield and particle size distribution. IntroductionMetal nanoparticles (NPs) are utilized in a wide variety of disciplines and can be employed as homogeneous or heterogeneous catalysts 1 as well as biological and molecular sensors. 2 A variety of NP synthetic strategies can be employed, but the most widely used methods utilize a simple metal salt, a reducing agent, and a colloid stabilizer. For example, the Schiffrin and Brust 3 method involves a biphasic water-organic solvent system where the reduction of a metal salt (e.g., HAuCl 4 or Na 2 PdCl 4 ) is performed in the presence of a colloid stabilizer (typically an alkyl thiol or (4-dimethylamino)pyridine) and a phase transfer reagent such as [N(C 8 H 17 ) 4 ]Br. When NaBH 4 is added this suspension, the alkyl thiol serves to arrest nanoparticle growth and carry the reduced metal particle into the organic solvent. Careful control over reagent concentrations allows for substantial control over particle sizes and dispersity.Polymers such as polyvinylpyrolidine (PVP) and poly(ethylene glycol) can be employed as colloid stabilizers in similar preparative schemes. 2 Starburst polyamidoamine (PAMAM) dendrimers are a specific class of nearly monodisperse, hyperbranched polymers that have been used to template nearly monodisperse nanoparticles. PAMAM dendrimers, which have open interiors and porous peripheries, serve as both particle templates and stabilizers and can be used in preparing a wide variety of mono-and bimetallic metal NPs. 4,5 In this synthetic scheme, metal precursors are first bound to the interior amine groups of the PAMAM dendrimer; addition of a reducing agent prepares particles that are essentially trapped within the dendrimer interior. The dendrimer mediated synthesis allows for greatly increased control over particle size and composition relative to traditional colloid preparation methods. For bimetallic particles, well-mixed and core-shell particl...

show abstract

Dendritic effect in polymer-supported catalysis of the intramolecular Pauson–Khand reaction

Abstract: A remarkable increase in catalytic activity and selectivity in the intramolecular Pauson-Khand reaction is observed for Co complexes, immobilised on second- and third-generation dendron-functionalized polystyrene, as compared with their analogues on non-dendronized support.

Cited by 58 publications

References 25 publications

Dendrons and dendritic catalysts immobilized on solid support: Synthesis and dendritic effects in catalysis

Dendrons and dendritic catalysts immobilized on solid support: Synthesis and dendritic effects in catalysis

Cascade Reactions Involving Pauson—Khand and Related Processes

Air and Water Free Solid-Phase Synthesis of Thiol Stabilized Au Nanoparticles with Anchored, Recyclable Dendrimer Templates

Contact Info

Product

Resources

About