Silicon catenates

Poly(hydrosilane)s are stable compounds and can be manipulated in the air only for a short period since they are oxygen-sensitive. The oxidized products obtained from poly(phenylhydrosilane) exposed to the air contain the units 119-122 without the formation of silyl hydroperoxides and peroxides. In particular, units 119,120, and 121+122 were present in the relative percentages of 27,54, and 19%, respectively, which means that more than 70% of the catenated silicons are altered. 

Poly(hydrosilane)s are stable compounds and can be manipulated in the air only for a short period since they are oxygen sensitive. In order to study the oxidation products, a xylene solution of poly(phenylhydrosilane)(Mw = 2340, Mw/Mn = 1.72) was refluxed (140 °C) for 12 h in a system exposed to the air [15]. Only minor changes were observed by GPC analysis whereas FTIR showed characteristic absorptions due to siloxane-type structures on the polymer backbone. A detailed NMR analysis, based on H NMR, Si INEPT and H- Si HMQC spectroscopies, indicated that the oxidized material contains the units 7-10 shown in Scheme 8.2. In particular, units 7,8 and 9+10 were present in relative percentages of 27%, 54% and 19%, respectively, which mean that more than 70% of the catenated silicons were altered. It has also been reported that silyl hydroperoxides and peroxides are not found as products in the autoxidation of poly(phenylhy-drosilane) [16]. 

The mechanism of the photochemical degradation of catenated silicon derivatives has received considerable attention (25). Substituted cyclic derivatives photochemically extrude a silylene fragment which can be intercepted by appropriate trapping reagents (e.g., trialkylsilanes or 2,3-dimethyl butadiene). This extrusion results in the formation of the corresponding ring contracted cyclopolysilane. The process continues upon additional irradiation until a cyclotetrasilane results which then undergoes... 

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. 

Even a preliminary investigation of the properties of some inorganic pol5miers reveals that some of them have unexpected properties. Polythi-azyl is an anisotropic electrical conductor and shows conductivity that is comparable to metals. At 0.26 K this polymer becomes superconducting [4, 5]. Polysilanes which contain catenated silicon atoms in a polymeric chain have several unusual properties. These polymers have a o-electron delocalization. They are radiation sensitive and many of them are thermo-chromic. Many members of this family also show nonlinear optical behavior [17, 19]. 

The first example of a polymeric product involving catenated silicon atoms was described by Burkhard in 1949 [8]. He prepared... 

Recently some bicyclo and cage structures based on P—P bonds have been obtained by reacting a mixture of RPCl and PCI3 with magnesium. Only the phosphorus skeletons are shown (Fig. 4.12). These discoveries show that the chemistry of catenated phosphorus derivatives, like that of catenated silicon compounds, is much more diverse than was imagined even ten years ago. 

There is then no significant formal difference between some series of catenated carbon compounds and catenated silicon compounds. 

Baumgartner J, Grogger C (2013) Catenated silicon compounds (cyclic and acyclic). In Chivers T (ed) Comprehensive inorganic chemistry II, Elsevier... 

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