Allyl-terminated dendrimers

The reaction of allyl-terminated dendrimers with ferrocenyldimethylsilane using Karstedt s catalysts resulted in dendrimers containing up to 243 ferrocenyl groups, as reported by Astruc and co-workers. Electrochemical studies showed that these dendrimers underwent chemically and electrochemically reversible oxidation processes.319,337,348... 

With few exceptions, substitutions on carbon have been achieved only at an early stage of the synthetic process, that is, on the starting o-carborane, but not by direct reaction at the [3,3 -Co( 1,2-C2B9H],)2] cage. Recently, the isolation of the synthon C<.-silyl-substituted cobaltabisdicarbollide Cs[l,l -p.-SiMeH-3,3 -Co(l,2-C2B9H,o)2] that allows the preparation of boron-rich polyanionic macromolecules via hydrosilylation reactions of vinyl- and allyl-terminaled dendrimers has been reported. ... 

Finally, a dendrimer containing 243 ferrocenyl units at the periphery was synthesized by ferrocenylsilation of an allyl terminated dendrimer. This macromolecule could be oxidized to the corresponding stable ferrocenium dendrimer and reversibly reduced back to the neutral complex. Cuadrado and coworkers have also been active in the synthesis of dendrimers containing ferrocene and cobaltocene moi-... 

Toluene solutions of Pd encapsulated within dendrimer-templated inverted micelles have been tested for catalytic activity by examining their effectiveness towards hydrogenation of allyl alcohol in organic solvents [19]. The reaction product was confirmed to be n-propanol by H NMR spectroscopy, and the turnover frequency, calculated from the rate of hydrogen uptake, was 760 mol H2 (mol Pd) h at 20 °C. This value compares favorably with the value of 218 mol H2 (mol Pd) h obtained for the same reaction carried out in water using Pd nanoparticles encapsulated in hydroxy-terminated dendrimers. 

The utilization of allyl alcohol as the nucleophilic reagent to prepare dendritic carbo-siloxanes was also reported by Lang and Brilning134,135. Using a second generation allyl-terminated carbosiloxane dendrimer, they were able to attach titanium moieties via a simple hydrosilylation reaction (equation 12)134. Lang and coworkers were also successful in binding cobalt moieties to ethynyl-terminated carbosiloxane dendrimers (e.g. equation 13)136,137. 

Scheme 8.5 Ferrocenylsilylation of the 81-allyl G2 dendrimer for the synthesis of ferrocenyl-terminated dendrimers...

Another example is the palladium catalyzed allylic substitution of 3-phenyl-2-propenyl-carbonic acid methyl ester to yield iV-(3-phenyl-2-propenyl)morpho-line reported by Reetz, Kragl and co-workers. This reaction was performed in the presence of phosphino-terminated amine dendrimers [17, 18] loaded with Pd11 cations as shown in Scheme 10. For this particular dendrimer with a molecular weight of 10 212 g/mol, a retention of 0.999 per residence time [35] was estimated in a membrane reactor with a SELRO MPF-50 membrane. It must be noted that a very high retention is a prerequisite for a continuous operating system, since a small leaching of the dendrimer leads to an exponential decrease in the amount... 

Fig. 19. Turn-over frequencies for hydrogenation of allyl alcohol and N-isopropyl acrylamide obtained in water using dendrimer-encapsulated Pd nanoparticles of constant average size. The hydroxyl-terminated PAMAM dendrimer generation varies from G4 to G8...

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). 

As a first step in realizing dendrimers with terminal allyl and chloro groups we prepared the first-generation octa[2-(dichloromethylsilylethyl)dimethylsiloxy]octasilsesquioxane (Gl-CI) via Pt-catalyzed hydrosilylation of the core molecule with dichloromethylsilane. Then each... 

In the next step of the dendrimer synthesis, treatment of the dichloromethylsilyl-capped product with allylmagnesium bromide provides eight terminal alkenes and provides the first-generation product. Subsequent cycles of hydrosilylation and alkylation provide the second- and third-generation dendrimers in similar fashion. The third-generation dendrimers were ultimately capped with phenols, pendant allyl- or alkoxy- groups, or phenylethylene units. ... 

Scheme 8.3 One-pot synthesis of polyolefin dendrimers till G3 (3 = 243 terminal allyl groups) using the silane HSiMe2Cl...

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. 

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