Cyclosilanes synthesis

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... 

The oldest known heterocycles are those containing oxygen as the hetero element. Kipping s work386) 382) with the first cyclosilanes (formed by a Wurtz synthesis from diphenyldichlorosilane) led to the discovery of two... 

Difunctional cyclosilanes, which are useful monomers for the synthesis of oligocyclic and cage like silanes, are obtained after chlorination of dodecamethylcyclohexasilane with SbCls in CCI4 [1, 2] or with Me3SiCl/AlCl3 [3], respectively. 

The yields of high polymer from this synthesis depend on the exact conditions and the nature of the substituent groups, but are typically low, from a few percent up to 60-70% in the most favorable cases. The by-products are mainly cyclosilanes, (RR Si) where n = 4 6. The molecular weight distributions of the polymers obtained by this procedure are usually bimodal, as shown in Figure 5 Various attempts have been made to improve the sodium condensation, including sonication and the addition of crown ethers and other additives, with some success. ... 

In addition to acyclic silicon compounds, this resolution method was successfully applied in the case of the cyclosilanes represented in Figure l17"19. As an example, the synthesis and resolution of 2-(l-naphthyl)-2-sila-l,2,3,4-tetrahydronaphthalene is depicted in Scheme 217. 

The photolysis of cyclosilanes with 254-nm UV light leads to elimination of divalent Si intermediates (silylenes), and reclosure of the ring. In addition to being a source of silylenes, this reaction is useful in the synthesis of cyclosilanesIn the permethyl series, photolysis of (Me2Si)g leads successively to (Me2Si)j and (Me2Si)4 ... 

As already shown above for cyclotrisilanes, ohgosilanyl dianions are convenient building blocks for the synthesis of cyclosilanes with different substitution pattern [47, 96, 108]. l,l,2,2-Tetrakis(trimethylsilyl)tetramethylcyclotetrasilane which forms in the oxidative coupling of the 1,4-dipotassium compound (Scheme 8) can... 

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