Silicon-containing compounds

II Nam Jung and Bok Ryul Yoo, Synthesis of Novel Silicon-Containing Compounds... 

The radical addition of bromoform to ketensilylacetals has been described, initiated with AIBN or Et3B (ref. 12). The reaction yields polyfunctional silicon-containing compounds of CHBr2C(R)CBr(OR )OSiR type or products of their conversions (hydrolysis, fragmentation of R etc.). 

Even though silicon is extremely abundant, only one silicon-containing compound appears in the list of top 50 industrial chemicals. That is sodium silicate, Na2 Si03, used for the manufacture of silica gel and glass. Nevertheless, with the advent of the electronic age silicon has become an extremely important substance that is the primary ingredient of most semiconductors. Because these are microscale devices, the quantity of production of silicon remains small compared with that of fertilizers and construction materials. Although relatively small in quantity, the value of silicon products is quite high. 

Summary The importance of structural studies for the identification of small molecules and for the interpretation of their reactivity is illustrated with examples of silicon-containing compounds. Such compounds are best studied in the gas phase, so that their structures are undistorted by intermolecular interactions, and may be compared with those calculated theoretically. Examples are given of silicon compounds which show major differences between their gas and solid phase structures, even when the intermolecular interactions are quite weak. 

Figure 5. Silicon-containing compounds studied by electron diffraction.

Cf. the review on Molecular States of Silicon Containing Compounds by H. Bock, Angew. Chem. 1989, 101, 1659 Angew. Chem. Int. Ed. Engl. 1989, 28, 1627 and references therein. 

Impregnations using Silicon-containing Compounds 7.3.1 Inorganic Silane Impregnations... 

The importance of carbon-centred radical cyclizations in organic chemistry has been documented in the large number of papers published each year and numerous reviews and books dealing with this subject. In Chapter 7 the reader can find a collection of such processes mediated by organosilanes. The silicon-centred radical cyclizations have instead received very little attention, although there has been a growing interest in silicon-containing compounds from a synthetic point of view, due to their versatility and applicability to material science. As we shall see, this area of research is very active and some recent examples show the potentiality of silyl radical cyclization in the construction of complex molecules. 

Cyclic silicon-containing compounds such as 61 undergo electrophilic attack at carbon with hydrogen peroxide to furnish the stereodefined diol 62 (Equation 12) <2003OL3875>. 

Several tests with silicon containing compounds as therapeutics in human medicine have already been crowned with success. In France certain organosilicon preparations, DNR and RDN (compare Chap. 5.5), are used in the treatment of cardiovascular diseases, cancer and virus infections. In the Soviet Union extensive clinical tests with ointments of l-(chloromethyl)- and 1-ethoxysilatrane as possible drugs for treatment of different typs of alopecia were successful (compare Chap. 5.1). Further clinical studies showed that l-(chloromethyl)silatrane is also very promising in treatment of wounds and bums. In a Swedish hospital patients with poorly differentiated prostatic carcinoma were treated with 2,6-c/s-diphenyl-hexamethyl-cyclo-tetrasiloxane (Cisobitan ) the clinical study also yielded promising results (compare Chap. 5.3). 

However, synthesis and biological screening of hundreds of novel silicon containing compounds resulted in the discovery of a large number of interesting bioactive framework structures, from which only a few characteristic examples are represented in this chapter. 

Tricyclic Silicon Containing Compounds with Potential Psychotropic Activity... 

X-ray diffraction analyses of some tricyclic silicon containing compounds with potential psychotropic activity have been carried out93, 100, 101 The experimental dihedral angles a are summarized in Table 12. 

When a toluene solution of a mixture of cyclotrisilane 34 and cyclohexyl isocyanate (or f-butyl isocyante) was heated at 70 °C, cyclic di- and trisiloxanes 37 and 38, i.e. the cyclic dimer and trimer of the silanone 36, were obtained together with the corresponding isonitrile RN=C. The formation of 37 as well as 38 was completely suppressed in the presence of hexamethylcyclotrisiloxane (19 D3) instead, quantitative conversion of 35 into 39, the formal insertion product of the silanone 36 into the Si—O bond of D3, occurred (Scheme 14). Since neither cyclodisiloxane 37 nor cyclotrisiloxane 38 reacted with D3 under the reaction conditions, the possibility that 37 or 38 is the precursor of 39 was ruled out. Whereas the oxidation of 35 with cyclohexyl and t-butyl isocyanates proceeded with exclusive formation of 37 and 38 (as the silicon-containing compounds) the reaction of 35 with phenyl isocyanate resulted in the formation of 37 in low yield. Furthermore, in this case the presence of D3 did not totally suppress the formation of 37. According to the authors, these results indicate that the oxidation of 35 with cyclohexyl and f-butyl isocyanates appears to use other reaction channels than that with phenyl isocyanate. 

Roberts2 has studied the substitution of trimethylallylsilicon by mercuric chloride in solvent acetonitrile. The substitution is complex, since there is formed not only the expected trimethylsilicon chloride (50 %) and allylmercuric chloride (50 %) but also an unidentified silicon-containing compound denoted as X. Furthermore, it was also shown that the action of trimethylsilicon chloride on trimethylallylsilicon afforded X and unchanged trimethylsilicon chloride. The overall reaction was formulated as... 

E. Magnusson, Tetrahedron, 41,2945 (1985). Substituent Effects in Second Row Molecules. Silicon-Containing Compounds. 

R. Walsh, Acc. Chem. Res., 14, 246 (1981). Bond Dissociation Energy Values in Silicon-Containing Compounds and Some of Their Implications. 

Do we now know enough of theoretical and practical interest regarding silicon compounds The answer is, we do not. Many of the silicon-containing compounds which today are of great technological importance were unknown a few decades ago and have originated from pure research. This basic research has generated many unanswered questions so that there is still much to be done in this field. 

The silyl-modified Prins reaction and the silyl-modified Sakurai reaction are common methods employed for dihydropyran (and tetrahydropyran) synthesis, and are in fact the same reaction. For the sake of clarity, the term silyl-Prins cyclization is adopted herein. A review of the use of silicon containing compounds in reactions of this type is available <1995CRV1375>. 

FIGURE 6.8 Chemical shift ranges for various silicon-containing compounds. Adapted from Bruker Almanac 1995... 

Metal hydroxides in combination with various silicon-containing compounds have been used to reduce the amount of additive required to achieve a required level of flame retardancy in a variety of polymeric materials, including polyolefins.62-63 Systems that have been used contain a combination of reactive silicone polymers, a linear silicone fluid or gum, and a silicone resin, which is soluble in the fluid, in addition to a metal soap, in particular magnesium stearate. However, there is little insight given into how these formulations work. 

Table XI contains data for silicon- and tin-containing complexes, chiefly from Mignani, Simon, and their co-workers. Figure 12 displays representative examples with large nonlinearities. It has been suggested from studies with the silicon-containing compounds that the trimethylsilyl group can function as both a donor and an acceptor, being a weak acceptor in [Si-Me3(C6H4-4-NMe2)].139 As this complex has a similar /3 value to...

A range of silicon-containing compounds is known (see Figure 6.2). There is little question that polymeric diversity is possible using silicon, rather than carbon, as a scaffolding. 

There arc many reactions in organic chemistry in which an Me3Si group acts like a proton—Chapter 47 will detail some more reactions of silicon-containing compounds. Just as acidic protons are removed by bases, silicon is readily removed by hard nucleophiles, particularly F" or RO-, and this can promote an elimination. An example is shown here. 

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