The Direct Synthesis of Organosilicon Compounds

Peroxy Compounds of Transition Metals J. A. Connor and E. A. V. Ebsworth The Direct Synthesis of Organosilicon Compounds J. J. Zuckerman... 

Organometals containing metal-metal bonds have become more important in recent years. Of especial interest are those compounds with both representative and transition metals. These have been known for over 30 years 130), but have become well known only comparatively recently 69) they provide a link (both literally and figuratively) between the two areas of organometallic chemistry. The growing commercial interest in the silicones has spurred research in organosilicon chemistry, especially polysilane chemistry. Work in this area has been reviewed by Kumada 159). The disilane fraction from the direct synthesis of methylchlorosilanes contains a mixture of compounds of type (CHa) -Clg. Sig, which are readily converted to hexamethyldisilane. This may then be converted to the chloride in a two-step synthesis 160) ... 

The synthesis of organosilicon compounds by the direct reaction of Si with methyl chloride is a commercially important process. 

Transition metal catalyzed carbene insertion into the Si—H bond provides a direct and efficient method for the synthesis of organosilicon compounds. When chiral spiro diimine ligand (/ )-24a was applied in Cu-catalyzed asymmetric insertion of a-diazo-a-arylacetates with silanes, the Si—H insertion products were obtained in high yields (85-97%) and excellent enantioselectivities (90-99% ee) (Scheme 51) [26a],... 

As in other preparative methods for organosilicon compounds, the direct synthesis produces a mixture of methylchlorosilanes rather than the single compound shown in equation 3. Besides dimethyl-dichlorosilane, the mixture usually contains silicon tetrachloride, tri-chlorosilane, methyltrichlorosilane, methyldichlorosilane, trimethyl-chlorosilane, and even silicon tetramethyl. Under proper conditions, dimethyldichlorosilane is the principal product. Of the other compounds, methyltrichlorosilane usually is next in abundance this substance finds use in the cross-linked methyl silicone resins, or it can be methylated further by the Grignard method to increase the yield of dimethyldichlorosilane. There is no way of recycling it in the direct process, and so supplemental operations are required for the conversion. The interconversion of this and the other minor products of the direct synthesis, involving the exchange of methyl and chlorine groups as desired, has been a special study in itself.10... 

Side by side with this, the application of organosilicon compounds where organic radicals are bound to silicon atoms through Si-C bonds for chemical modification is in very many cases hampered by the absence of a corresponding modifier or by its low reactivity relative to surface sites. As a consequence, of great importance is the development of methods of the synthesis of surface chemical compounds with Si-C bonds directly on silica surface. 

Of the alkylhalosilanes the ethyl as well as the methyl compounds323,327 can be obtained by the direct synthesis with higher homologs decomposition of the alkyl groups increases greatly at the higher reaction temperatures required, and many by-products with little of the organosilicon compound are formed. 

The first example of the hydrosilylation, that is, the reaction occurring between trichlorosilane and 1-octene in the presence of acetyl peroxide, was reported in 1947 by L. H. Sommer (1), but the discovery in 1957 of hexachloro-platinic acid as a very efficient catalyst by J. L. Speier (2) from Dow Coming became a strategic point for wide and common application of the reaction as one of the most fundamental and elegant methods explored over the next 50 years for laboratory and industrial synthesis of organosilicon and other related silicon compounds, which can also be directly subjected to organic synthesis. 

Summary The formation, reactivity, and cycloaddition behavior of neopentylsilenes towards suitable reaction partners is described. Especially l,l-dichloro-2-neopentylsilene. Cl2Si=CHCH2Bu (2) - easily obtained from vinyltrichlorosilane and LiBu - is a useful building block for the synthesis of SiC four membered ring compounds. These can be converted into the isomeric Diels-Alder and retro ene products upon thermolysis reactions. The mode of the silenes cycloaddition reactions ([4+2] vs [2+2] addition) can be directed by either the substitution pattern at the Si=C moiety, the choice of reaction partners or the conditions. Furthermore the products resulting from cycloaddition reactions open up a wide variety of following reactions, which possibly will lead to new organosilicon materials or pharmaceutical compounds. 

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