Carbosilane dendritic macromolecules

Figure 7. Roover s synthesis of carbosilane dendritic macromolecules...

Spin-coating films of other compositionally different dendritic macromolecules such as carbosilane dendrimers and hyperbranched poly(styrene) were studied by Sheiko et al. [20-22] using tapping mode AFM. 

Recently, dendrimers, which are hyperbranched macromolecules, were found to be an appropriate support for polymer catalysts, because chiral sites can be designed at the peripheral region of the dendrimers (Scheme 5). Seebach synthesized chiral dendrimer 14, which has TADDOLs on its periphery and used an efficient chiral ligand in the Ti(IV)-promoted enantioselective alkylation [21]. We developed chiral hyperbranched hydrocarbon chain 15 which has six p-ami-no alcohols [22], It catalyzes the enantioselective addition of diethylzinc to aldehydes. We also reported dendritic chiral catalysts with flexible carbosilane backbones [23]. 

Dendrimers are well-defined hyperbranched macromolecules and have been applied to the preparation of the dendrimeric catalysts [37]. Activities of the den-drimeric catalysts are generally comparable to those of the parent low-molecular-weight catalyst. In some cases even higher activities can be observed with the dendrimeric catalyst by means of so called dendritic effects [38]. Piers et al. developed (perfluoroaryl)borane-functionalized carbosilane dendrimers (66), which were used as Lewis acid catalysts for the hydrosilation of acetophenone [39]. In the presence of (66) as a catalyst, the hydrosilylation of acetophenone cleanly proceeded to essentially 100% conversion over the course of several minutes at 5% catalyst loadings at room temperature as shown in Scheme 19.16. 

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