Polysilanes polycyclic

Ladder polysilanes constitute a special case of fused polycyclic silicon macromolecules, in which cyclotetrasilane rings systematically catenate to form a silicon double helix, comprising two multi-linked silicon chains. Work in this area was initiated in this area by Matsumoto in 1987, and now comprises an integral part of the literature on higher-dimensionality polysilanes. 

Several classes of polycyclic polysilanes, such as the octasilacubanes and the hex-asilaprismanes, have been synthesized100, but little is known about the photochemical behavior of the silacubanes which appear to be stable toward ultraviolet radiation. The silaprismanes, such as 195, on the other hand, were observed to rearrange to the Dewar benzene isomer 196, using 340-380 nm radiation101. The Dewar benzene reverted to the... 

The parent cyclotetrasilane Si Ix and all the perfluorinated cyclopolysilanes are so far still unknown. More recently, the efforts in cyclopolysilane chemistry are mainly directed towards polycyclic and cage-like compounds and towards partially functionalized derivatives, which may be used as synthons for larger polysilane frameworks. 

The partially chlorinated cyclosilanes are valuable starting materials for the synthesis of other derivatives like di- and polycyclic polysilanes (see Section V.A). The dehalogenative coupling with alkali metals, however, only gives low yields and many side products are formed. Salt elimination of cyclosilanyl halides and cyclosilanyl alkali metal compounds... 

In contrast to annelated polycyclic polysilanes, where two cyclopolysilane units share two common silicon atoms, in linearly connected polycyclosilanes mainly two or three polysilane rings are linked by exocyclic Si—Si bonds. Selected compounds, which recently have been described in the literature, are presented in Scheme 20. More details and bibliography can be found elsewhere5d 22. 

Nonamethylcyclopentasilanyl-potassium, Me9Si5K, can be prepared via a mercury-potassium exchange reaction from bis(cyclopentasilanyl)mer-cury, (Me9Si5)2Hg, which is obtained by the reaction of hydro-cyclopenta-silane with (t-Bu)2Hg (Scheme 22) (87). This potassium reagent offers a new route to permethylated polycyclic polysilanes. 

Little is yet known of cage polysilanes, although many such structures should be possible. In the permethyl series when Me2SiCl2 and MeSiClj are cocondensed with Na-K alloy in THF in the presence of naphthalene, six different polycyclic compounds are produced, all in small yield, along with (Me2Si)g and polymer ... 

Figure 1. Polycyclic polysilanes and polygermanes prepared via reductive coupling of RMX3 or RX2M-MX2R...

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