Conjugated example: silicon

This might be the reason why polysilanes are still not as commonly used as, for example, silicones, though their electro- and photochemical properties resulting from a o-conjugation along the Si-Si-chain nominate them as promising candidates for technical applications [3]. 

While there are few examples of conjugate additions of either a-oxygen- or a-silyl-stabilized carbanions, Tamao and Posner have reported two hydroxymethyl synthons ["ClfcOH] (246 and 247) which show synthetic promise. Additions with the silicon-based synthon (246) is restricted to 2-cyclohexen-l-ones and work-up requires a successive acid and base procedure that is incompatible with sensitive molecules,188a-b while the tin-based synthon (247) is more versatile and the hydroxyl group is obtained under neutral conditions (Scheme 83).,88c... 

For l,3,2(A2)-diazasilacyclopentene 83, the following Raman lines at 650, 991, 1178, 1566, 1573 cm-1 were reported in the solid state. The intensive doublet at 1566 and 1573 cm-1 was assigned to the (C=C) stretch vibration. The observed bathochromic shift of this band in the spectra of compound 83 compared to heterocyclic compounds having a tetravalent silicon, for example, 93, and the significant intensity enhancement of this band indicates cyclic conjugation in molecule 83 <2000JST329, 2004JA4114>. 

If the 1,5-diearbonyl compound is required, then an aqueous work-up with either acid or base cleaves the silicon-oxygen bond in the product but the value of silyl enol ethers is that they can undergo synthetically useful reactions other than just hydrolysis. Addition of the silyl enol ether derived from aeetophenone (PhCOMe) to a disubstituted enone promoted by titanium tetrachloride is very rapid and gives the diketone product in good yield even though a quaternary carbon atom is created in the conjugate addition, This is a typical example of this very powerful class of conjugate addition reactions. 

In the same year, Tokitoh and coworkers have succeeded in the synthesis and isolation of the first stable 2-silanaphthalene 97 by taking advantage of the steric protection afforded by the Tbt group (Scheme 36) °. These two compounds 94 and 97 should be noted as the first examples which showed that double bonds containing a silicon can make a conjugated system as well as the parent carbon analogues. In 2000, a stable silabenzene 98, a much simpler sUaaromatic system than 97, was also synthesized and isolated using a similar kinetic stabilization method (Scheme 36). ... 

At a hrst glance, a bonded polymers may be considered as being characteristically different from n bonded polymers. However, there are several systems which truly behave very much like Jt polymers. Characteristic examples include polysilanes, whose backbone is a <7 bonded silicon zig-zag chain with alkylic side groups (Rabolt et al., 1986). The similarity to the Ji-.systems results from the fact that there is an efficient overlap of adjacent orbitals leading to conjugated [Pg.381]

Conducting (conjugated) polymers have a unique set of properties The electronic properties of metals and semiconductors and the processing advantages and mechanical properties of polymers. It is the and that makes conducting polymers special materials. There are, after all, many excellent metals for example, copper, nickel, silver and gold, to name but a few. Similarly, there are many excellent semiconductors. Indeed, the sophisticated modem electronics industry uses silicon as the semiconductor of choice. It would be difficult to improve on the quality of copper as a metal or silicon as a semiconductor. 

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