Silicon-containing dendrimers

Although the first publication on dendrimers appeared in 1978 [ 1 ] it is only in 1990 that the first report on phosphorus-containing dendrimers was published [2] i.e. after numerous papers devoted to the synthesis of organic dendrimers and practically at the same time than the description of a silicon containing dendrimer. 

Krska, S. W. Son, D. Y. Seyferth, D. Organosilicon Dendrimers. In Silicon-Containing Polymers. The Science and Technology of Their Synthesis and Applications-, Jones, R. G., Ando, W., Chojnowski, J., Eds. Kluwer Dordrecht, 2000 pp 615-641. 

Alonso et al. prepared ferrocenyl silicon dendrimers [67], which could be used as mediators in glucose biosensors, based on glucose oxidase [68, 69], The ferrocenyl units are located at the end of long, flexible, silicon containing branches and serve to electrically connect the enzyme to the electrode. The flexibility of the dendrimer is proposed to play an important role in the interaction with the redox center of glucose oxidase. 

VI. SYNTHESES OF SILICON-CONTAINING DENDRIMERS AND POLYMERS USING HYDROSILYLATION... 

Siloxanes, prepared in 1989 as representatives of silicon-based dendritic molecules ( silicodendrimers ), were the first dendrimers to contain heteroatoms other than the usual ones (N, O, S, halogens) [68]. As with the phosphodendri-mers (Section 4.1.10), their readily modifiable architecture and their pronounced thermostability hold promise of applications, for example, in the form of carbo-silanes as liquid-crystalline materials and catalyst supports. They can be subdivided into a number of basic types and their properties are presented below with the aid of characteristic representatives ... 

In a few cases, interaction between equivalent electroactive ferrocene units has been observed. One example is the silicon-based dendrimer 6, containing 16 ferrocene units, which upon oxidation in CH2CI2 shows two well-separated reversible... 

The study of dendritic polysilanes is a relatively new trend in silicon chemistry [1], However, first results suggest interesting properties for these compounds. Lambert and coworkers pointed out that their polysilane dendrimer, which contains 27 heptasilane chains possesses a very similar A ax value (272 nm) compared to the parent heptasilane (266 nm) but shows an extinction coefficient about ten times larger. Comparison of the number of silicon atoms in the molecules (13 V5 7) indicates an amplification of extinction per silicon atom of about 5 [la]. 

Catalytic hydrosilylation provides a convenient route to silicon-containing den-drimers. Combinations of hydrosilylation with alkenylation (usually allylation and vinylation) and ethynylation give powerful protocols for the rapid and efficient synthesis of silicon-containing dendrimers (mostly carbosilanes and carbosilox-anes) [4]. This topic has recently been reviewed by Majoral [31] and Schlenk and Frey [32], At present carbosilane dendrimers are the most important class of Si-based dendrimers (cf. also Section 3.2.2). 

In Kharasch addition to acrylic acid ester that is catalyzed by nickel complexes with silicon-containing dendrimers modified with a chelate aryldiamide ligand, the catalyst activity is lower than that of a low molecular weight analogue, van Koten and coworkers assumed that this is due to the small distance between nickel atoms on the dendrimer surface and to the formation of mixed-valence binuclear complexes [114, 126, 127]. 

Dvornic, P. R., PAMAMOS The First Commercial Silicon-Containing Dendrimers and Their Applications. J. Polym. Sci., Part A Polym. Chem. 2006, 44, 2755-2773. 

Modifications of organic polymers with organosilicon compounds were reviewed by McGrath and co-workers (32). Synthesis and properties of silicon-containing dendrimers including hydrosilylation were the subjects of the review by Majoral and Caminade (33). Functionalization of silsesquioxanes via hydrosilylation (34,35) and production of new composite materials (36) were also presented. 

The hydrosilylation processes of carbon-carbon multiple bonds, applied in the field of polymer chemistry and materials science, are described in part three (section 4) of this article. It includes functionalization (and cross-linking) of polysiloxanes and (poly)silsesquioxanes as well as hydrosilylation polymerization of difunctional organosilicon monomers besides the application of hydrosilylation in the synthesis of silicon-containing dendrimers and hybrid organic-inorganic materials. 

Functionalized (Poly)Silsesquioxanes and Organosilicon Den-drimers. One of the most rapidly developing branches of organosilicon chemistry is that of functionalized (poly)silsesquioxanes (34,36,370-372) and silicon-containing dendrimers (4,33,373-375). They are characterized by the presence of a large number of functional groups on the surface therefore, they can be very useful precursors for the synthesis of new nanomaterials. 

Nakayama and Lin have reported on the first organosilicon dendrimer SisTie, containing 16 2,5-thienylene rings, connected via tetrasubstituted silicon atoms [123]. SisTie was synthesized by the reaction between a tetralithium... 

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