Cage polysilane

Polysilane cages are usually prepared by the reductive coupling of bulky organohalosilane precursors mainly with Li, Na or Mg metal as shown in equations 22 and 23 for octakis(2,6-diethylphenyl)octasilacubane or hexakis(2,6-diisopropylphenyl)hexasilaprismane90 91. 

Another recent study98 does not deal with the formation of homocyclic polysilane cages, but with the insertion of oxygen into a strained bicyclic ladder polysilane. The introduction of heteroatoms into ladder polysilane skeletons seems interesting because of possible perturbations of the cr-(Si—Si) conjugation system. The oxidation of decaisopropylbicy-clo[2.2.0]hexasilane with a deficient amount of m-chloroperbenzoic acid (0.7 equivalents) affords the monooxidation products decaisopropyl-7-oxabicyclo[2.2.1]heptasilane in 32% yield and decaisopropyl-2-oxabicyclo[3.2.0]heptasilane in 18% yield (equation 27), which can be easily separated by HPLC. 

In summary, in addition to its aesthetic quality, octasilacubane is also unique for its unusual reactions ascribable to the strain and polysilane cage structure. We believe that these results are only a part of its diversity, and further investigation is now in progress. 

A number of cage polysilanes with silicon architectures in the shapes of a cube, trigonal prism, and tetrahedron have also been prepared and crystallographically analyzed. These were synthesized prior to the years covered in this chapter, but as they were not mentioned in the previous organopolysilane chapter, their structures will be briefly noted here. 

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. 

West et al. recently found 8) that dimethyldichlorosilane and methyl-trichlorosilane react with Na/K alloy in the presence of naphthaline in THF to yield bicyclic and cage polysilanes Si7mej2) Si8me14, Si9mei6,... 

Keywords cage polysilane, silicon polyhedranes, reactions... 

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 ... 

Cage polysilanes undergo only two chemical reactions. Photolysis of Mcj Sig leads to silylene extrusion and the formation of the 2.2.1-heptasilabicyclo-heptane ... 

A series of complex cage polysilanes has been synthesized starting from t-BuCl2SiSiCl2Bu-t by Masamune and coworkers . When t-BuCl2SiSiCl2Bu-t is treated with lithium naphthalenide in DME, reductive oligomerization takes place and, somewhat surprisingly, tricyclo[2.2.0.0 ]hexasilane and tetracyclo[3.3.0.0 . 0 ]octasilane derivatives are obtained (Scheme 25). The unexpected structures of the products were established by double quantum coherence Si-NMR spectroscopy and X-ray crystallography. 

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