Platinum hyperbranched

Well-defined complicated macromolecular structures require complex synthetic procedures/techniques and characterization methods. Recently, several approaches leading to hyperbranched structures have been developed and will be the focus of this section. The preparation of hyperbranched poly(siloxysilane) has been reported [198] and is based on methylvinyl-bis(dimethyl siloxysilane), an A2B type monomer, and a progressive hydrosi-lylation reaction with platinum catalysts. An appropriate hydrosilylation reaction on the peripheral - SiH groups led to the introduction of polymeric chain (PIB, PEO) or functional groups (epoxy, - NH2) [199]. 

The same hyperbranched polyglycerol modified with hydrophobic palmitoyl groups was used for a noncovalent encapsulation of hydrophilic platinum Pincer [77]. In a double Michael addition of ethyl cyanoacetate with methyl vinyl ketone, these polymer supports indicated high conversion (81 to 59%) at room temperature in dichloromethane as a solvent. The activity was stiU lower compared with the noncomplexed Pt catalyst. Product catalyst separation was performed by dialysis allowing the recovery of 97% of catalytic material. This is therefore an illustrative example for the possible apphcation of such a polymer/catalyst system in continuous membrane reactors. 

Frey and Van Koten et al. [40-42] reported on the noncovalent encapsulation of sulfonated pincer-platinum(II) complexes in readily available amphiphilic nanocapsules based on hyperbranched polyglycerol, possessing a reverse micelle-type architecture. The incorporated platinum(II) complexes showed catalytic activity in a double Michael addition, albeit with decreased activities compared to the free pincer complex. Due to the size of... 

Scheme 2 Synthesis of pertosylated hyperbranched polyglycerol followed by partial substitution of tosyl groups with NCN-pincer platinum(II) carboxylates...

For the applicability of these polymer-stabilized water-soluble nanoparticles in catalysis, the hydrogenation of olefins (i.e., isophorone) with the hyperbranched PEI-GLU-encapsulated platinum nanoparticles was investi-... 

In Sect. 2 of this overview, the NCN-pincer platinum(II) complex was covalently attached to hyperbranched polyglycerol by substitution of tosylate groups to obtain catalyst 4. This NCN-pincer platinum complex may also be noncovalently immobilized on polyglycerols, and the activity/selectivity of these systems in catalytic reactions has been investigated. 

A hyperbranched polycarbosilane (hb-P22) was prepared by platinum-catalyzed polyhydrosilylation of methyldiethynylsilane 22 (Scheme 11) [43]. The tacky, highly soluble and stable polymer underwent thermo- and photo-induced cross-linking reactions through the peripheral ethynyl groups. 

Scheme 30.13 Synthesis of a hyperbranched polymer from a platinum-containing acetyUde monomer.

Hi) Non-covalent approaches to gold glyconanoparticles. Other protocols have been reported for the synthesis of GNPs in which the carbohydrates are non-covalently attached to the metal eluster. Saceharide-modified hyperbranched poly(ethylenimines) were used to elaborate eopper, silver, gold, and platinum nanoparticles. 12-a-C-Ribofuranosyl and ribopyranosyl dodecanoic acids were heated with silver nitrate in dilute alkaline solution to afford water-soluble 15 nm silver GNPs. ... 

The polyaddition by means of a platinum catalyst yielded hyperbranched macromolecules with one terminal SiH group and ti+1 vinyl groups or 2n+ vinyl groups in the case of the triallyl compound, n being the degree of polymerization (Scheme 1). 

Fig. 1. SEC elugrams of hyperbranched polymethyidiundecenylsilane synthesized using different catalysts (platinum concentration = 0.0006 wt. % (PC072, PC085, Speier s catalyst), 0.0002 wt. % (Pp ) solvent n-hexane T = 20°C reaction time 7 d). PC072 ( --------------), PC085 (----),PP (.) and Speier s catalyst (--).

Scheme 2.2 Synthesis of hyperbranched platinum-containing polyyne from AB -type monomers...

The platinum-catalyzed or thermal ring opening polymerization of the substituted silacyclobutane monomers yields linear polycarbosilanes. The platinum-catalyzed hydrosilations of the AB (allyl) and AB2 (diallyl) monomers yield linear and hyperbranched polycarbosilanes, respectively. A wide range of random copolymers are readily available from polymerization of mixtures of the silacyclobutane or AB and AB2 monomers. The preparation of random copolymers is often of interest for achieving desired physical properties. 

A second method was based on the direct assembly of platinum building blocks, where hyperbranched multipods with high aspect ratios could serve as the nanostructured precursors. A network of platinum nanowires directly assembled from a solution phase is shown in Figure 10.15. Unlike the networks made from templates, these assembled networks could either be disassembled into individual multipods in dispersion form, or sintered into connected networks. 

Figure 10.15 Platinum 3-D network from the self-assembly of hyperbranched multipods.

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