Silicon-containing rings

In one approach, six-membered silicon-containing rings are pyrolized giving mixed car-bosilane preceramic polymers through heating to 400°C, and subsequently forming silicon carbides or poly(carbosilanes) at 800°C. 

As expected, 3-Li reacts readily with electrophiles protonation with cyclopentadiene or treatment with trimethylchlorosilane gave 3-H and 3-TMS, respectively (Schemes 1 and 2). Surprisingly, the reactions with 1,2-dibromoethane or diaryldichlorosilane gave rise to the formation of the cyclotrisilane 1 in moderate yield. Other silicon containing ring systems should be accessible via reaction with bis-electrophiles. 

Reactions of CpfSi with aldehydes and ketones lead to products that are different from those observed in analogous reactions with transient silylenes. For instance, as indicated in the first of reactions (b), when the silylene is combined with benzaldehyde, coupling of the organic groups occurs and a five-membered silicon-containing ring is the result (34% yield, compound 3). 

A limited amount of data exists for silicon-containing ring compounds. This is shown in Table 5. All the studies involved used combustion with an auxiliary fluorine compound, and so it is disappointing that for the four-membered ring compounds (siletane, disiletane) the agreement is so poor. Steele s values are taken to be the most reliable, both... 

TABLE 5. Standard enthalpies of formation of some silicon-containing ring compounds... 

Keywords Silicon-Containing Rings / Tin-Containing Rings / Ferrocenophane /... 

Conformations of silicon-containing rings. II a conformational study on silacyclo-hexane. Comparison of ab initio (HF, MP2), DFT, and molecular mechanics calculations. Conformational energy surface of silacyclohexane ... 

The situation for strained silicon-containing ring compounds has become if anything, more confusing since the previous review. The only new experimental data, are those for a series of siletanes " (silacyclobutanes), shown in Table 8. From these, strain enthalpies in the range of 109-120 kJmol can be calculated. These are slightly larger than an... 

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