Dendrimer-encapsulated palladium

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). 

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.

Fig. 16. Proposed structure of dendrimer-encapsulated palladium complex.

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... 

Supported catalysts involving palladium on carbon and dendrimer-encapsulated palladium and a polymer-supported phosphine palladium catalyst have facilitated C-C coupling reactions in SCCO2. Polymer-tethered substrates or amine bases have also been successfully used for the Mizoroki-Heck and Suzuki-Miyaura reactions in SCCO2. For example, REM resin underwent a Mizoroki-Heck reaction with iodobenzene to yield, after cleavage, ( )-methyl cinnamate 48 (74%) (Scheme 88). It is assumed that SCCO2 acts as a good solvent that swells the polymers and exposes reactive sites. 

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. 

Scott, R.W.J., Ye, H., Henriquez, R.R. and Crooks, R.M. (2003) Synthesis, characterization, and stabflity of dendrimer-encapsulated palladium nanopartides. Chemistry of Materials, 15,... 

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