Silicon—oxygen bonds metal halides

It has been noted (Section II,B,1) that reactions between transition metal carbonyl anions and silicon halides often fail to produce species containing silicon-transition metal bonds, and that such failure has been ascribed to nucleophilic attack by carbonyl oxygen. It is therefore interesting that compounds containing Si—O—C—transition metal linkages have recently been isolated from such reactions [Eqs. (105) (R = Me, Ph) 183) and (106)... 

The intermediate metal hydride has been isolated on occasion for Co and Mn , and Eq. (b) has actually been used to prepare silicon-metal bonds (see 5.2.3.2.2.). Inspection of Table 1 reveals the ease of reaction of Co2(CO)g compared with the other carbonyls. Normally this reaction is performed simply by condensing volatile silane onto the carbonyl in the absence of solvent and then allowing rapid reaction in the liquid phase at room temperature, but for the remaining carbonyls it is necessary to use elevated temperatures and sealed, evacuated tubes. The products are volatile and readily purified by vacuum fractionation or sublimation, but are often oxygen and moisture sensitive. The route is most efficient for RjSi derivatives of Co, Mn and Re, which are not generally obtainable by the reactions of silicon halides with metal carbonyl anions (see S.8.3.3.I.). In this way lCo(SiR,)(CO -] = Et, Phj, Clj -, (OEt)j, F/, ... 

Silicone Oils. Silicone refers to a siloxane polymer. The name itself derives from early research in which it was thought that oxygen was bound to silicon via a double bond such as found in a ketone. The simplest of these polymers are the poly(dimethylsiloxane)s. Poly(dimethylsil-oxane)s are made by hydrolyzing dimethyldichlorosilane with hydrochloric acid (9). Dimethyldichlorosilane is, in turn, made by the Rochow reaction. In this reaction, an alkyl halide (RX), methyl chloride in this instance, is treated with silicon metal in the presence of a catalyst (usually copper). The reaction results in a number of products that are separated by distillation (10). 

Some reactions of trimethylchlorosilane are summarized in Fig. 4.4. Many of these involve nucleophilic attack at silicon in which chlorine is substituted by another group. Alkoxysilanes are obtained using metal alkoxides or alcohols in the presence of pyridine. If the latter reaction is carried out in a non-polar solvent such as light petroleum, pyridinium hydrochloride is precipitated and may be filtered off, leaving the alkoxysilane in solution. Hydrogen chloride cleaves carbon-oxygen bonds in alkoxysilanes (as it does in ethers also) to form an alkyl halide and a siloxane ... 

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