Dendrimer-encapsulated palladium nanoparticles

Using a similar approach, Chechik and Crooks (73), modified the PAMAM dendrimer-encapsulated palladium nanoparticles with perfluoropolyether tails utilizing non-covalent ion-pair interactions. The catalytic hydrogenation of six substrates under biphasic conditions (toluene/ perfluoro-2-butyltetrahydrofuran FC-75) was investigated. Allyl alcohol, methyl acrylate, vinyl isopropenyl ether, and... 

Fig. 15. Schematic representation of the formation of an inverse micelle from a PAMAM dendrimer-encapsulated palladium nanoparticle.

Polymer-stabilized palladium nanoparticles (or nanoclusters) [125-127] have recently received increasing attention in the field of synthetic organic chemistry [128, 129]. Thus, for example, the poly(iV-vinyl-2-pyrrolidone) (PVP)-supported Pd particle catalyzed the Suzuki-Miyaura coupling in water [130]. Poly(amidoamine) (PAMAM) dendrimer-encapsulated palladium nanoparticles were designed and prepared to provide highly selective catalysts for hydrogenation of olefins [131-133]. Hyperbranched aromatic amides (aramids) and PS-DVB-methacryloylethylenesulfonic acid resin have also been... 

Poly(amidoamine) (PAMAM) dendrimer-encapsulated palladium nanoparticles were designed and prepared to provide highly selective catalysts for hydrogenation of olefins [131-133]. Hyperbranched aromatic amides (aramids) and PS-DVB-methacryloylethylenesulfonic acid resin have also been... 

Yeung, L.K., Lee, C.T. Jr, Johnston, K.P. and Crooks, R.M. (2001) Catalysis in supercritical CO2 using dendrimer-encapsulated palladium nanoparticles. Chem. Commun., 2290-1. 

R.W.J. Scott, H. Ye, R.R. Hemiquez, R.M. Crooks, Synthesis, Characterization, and Stability of Dendrimer-Encapsulated Palladium Nanoparticles, Chemistry of Materials 15, 3873, 2003. 

Niu Y, Yeung LK, Crooks RM. Size-selective hydrogenation of olefins by dendrimer-encapsulated palladium nanoparticles. J Am Chem Soc 2001 123 6840-6. 

Palladium and Platinum. PHIP has been used to study the hydrogenation of phenyl acetylene by colloidal palladium.In situ P NMR spectroscopy has been used to show the resting state of the [(Pr 2PCH2CH2CH2PPr 2)Pd(PR3)2] in the catalysis of the reaction of ethene with The size-selective hydrogenation of alkenes by dendrimer-encapsulated palladium nanoparticles has been investigated by NMR spectroscopy. 

Scott RWJ, Ye HC, Henriquez RR, Crooks RM (2003) Synthesis, characterization, and stability of dendrimer-encapsulated palladium nanoparticles. Chem Mater 15 3873... 

Crooks group prepared monodisperse (1.7 0.2nm) palladium nanoparh-cles within the interiors of three different generations of hydroxyl-terminated PAMAM dendrimers [41]. This process involved encapsulation of the nonselec-tive catalyst (the Pd nanoparticle) within a selective nanoporous cage (the dendr-imer). These dendrimer-encapsulated palladium nanoparticles were used as catalysts to hydrogenate allyl alcohol and four R-substituted derivatives in a metha-nol/water mixture. The results showed that higher-generation dendrimer encapsulated catalysts (DECs) or larger substrates resulted in lower turnover frequencies. 

Zhao et al (70) developed a method for the synthesis of dendrimer-encapsulated metal nanoparticles based on sorbing metal ions into (modified) PAMAM dendrimers followed by a reduction. Dendrimers encapsulating copper, palladium, and platinum nanoparticles have been prepared. Hydroxyl-terminated PAMAM dendrimers were used to prepare encapsulated palladium (PAMAM generations 4, 6, and 8) and platinum (PAMAM generations 4 and 6) nanoparticles. The dendrimer-encapsulated palladium and platinum nanocomposites catalyzed the hydrogenation reaction of allyl alcohol and N-isopropyl acrylamide in water 71). 

Aranishi K, Zhu QL, Xu Q. Dendrimer-encapsulated cobalt nanoparticles as high- performance catalysts for the hydrolysis of ammonia borane. Chem Cat Chem 2014 6 1375-9. Mizugaki T, et al. PAMAM dendron-stabilised palladium nanoparticles effect of generation and peripheral groups on particle size and hydrogenation activity. Chem Commun 2008 241-3. 

Bernechea M, de Jesus E, Lopez-Mardomingo C, Terreros P (2009) Dendrimer-encapsulated Pd nanoparticles versus palladium acetate as catalytic precursors in the Stille reaction in water. Inorg Chem 48(10) 4491-4496... 

Dendrimer-encapstdated catalysts are another area of active research for polymer-supported catalysts. The nanoparticles are stabilized by the dendrimers preventing precipitation and a omeration. Bimetallic nanoparticles with encapsulated metals (dendrimer-encapsulated catalyst DEC) from commercially available fourth-generation PAMAM dendrimers and palladium and platinum metal salts were prepared via reduction by Crooks and co-workers [34], following previous work in this area [35], The simultaneous incorporation of Pt and Pd reflects the concentrations in solution. The bimetallic DECs are more active than the physical mixture of single-metal DEC [35, 36] in the case of the hydrogenahon of allyl alcohol in water, with a maximum TOP of 230 h compared to TOP = 190 h obtained for monometallic palladium nanoparticles (platinum TOP = 50 h ). 

Recent developments aiming at highly active and versatile catalytic materials for Mizoroki-Heck and Suzuki reactions in various reaction media, including SCCO2, are exemplified by dendrimer-encapsulated metal (palladium) nanoparticles [121-123]. Although those systems are not yet fully developed and optimized, they have already delivered... 

FIGURE 9.3 a) UV-vis spectra of 2.5 0,M Pd3oG4NH2 solutions before (pH 3) and after (pH 8) reduction, b) Time-resolved UV-vis spectra of 2.5 pM PdjoGdNH solutions in the presence of 0.1 M KCl before (pH 3) and after (pH 8) reduction. Reprinted with permission from H. Ye, R.W.J. Scott, R.M. Crooks, Synthesis, Characterization, and Surface Immobilization of Platinum and Palladium Nanoparticles Encapsulated within Amine-Terminated Poly(amidomine) Dendrimers Langmuir 20 (2004) 2915. Copyright 2004 American Chemical Society. 

Gomez MV, Giuerra J, Velders AH, Crooks RM (2009) NMR characterization of fourth-generation PAMAM dendrimers in the presence and absence of palladium dendrimer-encapsulated nanoparticles. J Am Chem Soc 131 341-350... 

Ye HC, Scott RWJ, Crooks RM (2004) Synthesis, characterization, and surface immobilization of platinum and palladium nanoparticles encapsulated within amine-terminated poly(amidoamine) dendrimers. Langmuir 20 2915... 

While they are not strictly redox-containing dendrimers. Crooks and Zhao have encapsulated platinum and other metallic nanoparticles inside PAMAM dendrimers. The catalytic properties of these materials have been examined using cyclic voltammetry, and it was found that a gold electrode, modified with large hydroxyl-terminated PAMAM dendrimers containing clusters of 60 platinum atoms, was readily able to catalyze O2 reduction [98]. Similar results have been reported for palladium clusters encapsulated in the same hydroxyl-terminated PAMAM dendrimers [99]. 

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