Cyclopolysilanes synthesis

In order to quantify the dependence of the preferred ring size obtained in cyclopolysilane synthesis on the bulk of the substituent groups on the silicon Cartledge postulated a set of parameters derived from the rates of acid catalyzed hydrolysis of appropriate hydrosilanes8. The model, however, was applied only with limited success9. 

Catalytic dehydrogenative coupling of organohydrosilanes, a common method for the formation of linear polysilanes, can also be applied to cyclopolysilane synthesis. Thus, benzylsilane reacts to give all-fraws-hexabenzylcyclohexasilane in the presence of dimethyltitanocene (equation 3). However, extremely long reaction times are required and only moderate yields are obtained15. 

In the case of dichlorosilanes, oligomerization to form cyclopolysilanes occurs in high yields, with the product s ring size dependent upon the steric bulk of the starting silane (219). Boudjouk initially reported (221) the synthesis of West s novel disilene (222) upon sonication of lithium with the highly hindered bis(mesityl)dichlorosilane [Eq. (44)]. It is difficult, however, to obtain consistent results with this sonochemical synthesis of the... 

The increased reactivity of triflate groups bonded to silicon relative to halogen substituents can also be utilized for the synthesis of multifunctional cyclopolysilane transition metal derivatives, as has recently been shown for 1,3-disubstituted cyclohexasilanes104 (equation 35). 

Although the structures of cyclopolysilanes can be similar to the carbon analogs, the methods of synthesis are not. The majority of the systems studied result from the selfcondensation of R2SiCl2 or RR SiCl2 which provide cycles of different sizes and with identical substituents at each silicon center. Of course, it is possible to cocondense two different dichlorosilanes, however then not only are rings of different sizes produced but isomers within each ring size are generated265 and separation can be a real problem. Clearly this area of catenated silicon derivatives would benefit from other reaction methods. 

If an exactly equivalent amount of Li, or a deficiency, is used to condense Me2SiCl2, a product distribution is obtained in which the six- and eight-membered rings dominate among the oligomeric products (see Table 1) . This provides the best method for synthesis of (MejSOg. Higher cyclopolysilanes are also formed in this Li condensation. 

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