Functionalized silicon compounds

Recently we reported an easy route obtaining enamine-functionalized silicon compounds with a pentacoordinate silicon atom from organotrichlorosilanes and ethyIene-iV,iV -bis(2-hydroxyaceto-phenoneimine) (salen H2) [1]. 

SiCl4 is the starting material for the synthesis of organo-functional silicon compounds and is utilized in the manufacture of highly dispersed SiO, (pyrogenic silicic acid) and for the silization of metallic objects. Tetrafluorosilane (SiF4) see Section 1.7.1.3.2. Hexafluorosilicic acid (H2SiF6) see Sections 1.7.1.3.2 and 1.7.1.3.3. 

Functional silicon compounds R3SiX are also optically stable. Racemization is observed only in the presence of nucleophilic agents. Kinetic studies of the nucleophilically assisted racemizations of halogenosilanes, germanes, and stannanes have revealed that they involve two molecules of nucleophile in the rate-... 

More recently, the scope of the reaction has been extended and further mechanistic aspects have been discussed (ref. 37). Cleavage of C-Si bonds of organosilicon compounds is continually receiving much attention in view of its versatile utility in organic synthesis. With functional silicon compounds such as fluoro-, chloro-, alkoxy-, and aminosilanes, the oxidative cleavage of C-Si bonds, giving corresponding alcohols (ref. 38) (Scheme 16), is of special interest for the... 

Trihalogenosilyl compounds are of general importance as trifunctional precursors for the synthesis of highly functionalized silicon compounds such as branched silicones and silsesquioxanes. Trihalogenosilylstannanes and related germanes, being a kind of a-halogeno(metal)silane, would be most desirable precursors for further transformation. 

Chlorosilanes are the most important functional silicon compounds. As described above, chlorosilanes can be used for silicon—carbon and silicon—silicon bond formation. In addition, chlorosilanes can be converted into other functional silicon compounds, such as hydrosilanes, alkoxysilanes, and aminosi-lanes. Hydrosilanes, alkoxysilanes, and aminosilanes can be transformed furthermore into other functional silicon compounds. Combination of functional group transformation and silicon-carbon and silicon—silicon bond formation of chlorosilanes are essential for the construction of organosilicon clusters. 

The properties and applications of commercially important hydride functional silanes, ie, compounds having a Si—H bond halosilanes, ie, compounds having a Si—X bond and organosilanes, ie, compounds having a Si—C bond, are discussed hereia. Compounds having Si—OSi bonds are called sdoxanes or sihcones. Those having a Si—OR bond are called siUcon esters. Sdoxanes and siUcon esters are discussed elsewhere ia the Eniyclopedia (see Silicon COMPOUNDS, SILICON ESTERS SILICON COMPOUNDS, SILICONES). 

Transition-metal chemistry is currently one of the most rapidly developing research areas. The record of investigation for compounds with metal silicon bonds is closely comparable to that for silicones it was in 1941 when Hein discovered the first metal silicon complex, followed by Wilkinson in 1956. A milestone in the development of this chemistry was Speier s discovery of the catalytic activity of nobel metal complexes in hydrosilylation reactions in 1977. Hydrosilylation is widely used in modem organic syntheses as well as in the preparation of organo functionalized silicones. Detailed investigations of the reaction mechanisms of various catalysts continue to be subject of intense research efforts. 

R. Walsh, Thermochemistry, in The Chemistry of Organic Silicon Compounds (S. Patai, Z. Rappoport, Edits.), [The Chemistry of Functional Groups, (S. Patai, Edit.)], part 1, p. 371 ff, Wiley, New York 1989 H. Bock, B. Solouki, Photoelectron Spectra of Silicon Compounds, in The Chemistry of Organic Silicon Compounds (S. Patai, Z. Rappoport, Edits.), [The Chemistry of Functional Groups, (S. Patai, Edit.)], part 1, p. 555 ff, Wiley, New York 1989. 

I. Ojima, The Hydrosilylation Reaction, in The Chemistry of Organic Silicon Compounds (S. Pa-tai, Z. Rappoport, Edits.), [The Chemistry of Functional Groups, (S. Patai, Edit.)], part 2, p. 1479 ff, Wiley, New York 1989. 

One section in this review will deal with silyl cations, another with hypervalent silicon compounds. The concept of hypervalent sihcon compounds belongs, strictly speaking, to the class of Lewis base catalysis. However, since a Lewis base forms in situ with a silicon containing reagent or SiCl an intermediate, which functions as a Lewis acid to activate substrates during the reaction, we would also present a few examples in this review. Since silicon is a semimetal we leave it up to the reader to decide whether silicon catalysts should be considered as organocatalysts. 

Silicon compounds having Si-H, Si-N and Si-C bonds are reported to be effective as catalysts for HTPB-based propellants. Bum rate of propellant varies as a function of the Si content in the propellant formulation [252]... 

However, influence on functional groups in organic compounds by a silicon atom is also possible without (p- -d), interaction. In examples (CH3)3E1CH2C00H and (CH3)3E1CH2NH2 (El = C, Si) the silicon compound is the weaker acid and the stronger base. These effects are explained by a a-electron release for the silicon compounds, caused by the lower electronegativity of silicon. 

The silicon-metal doubly bonded compounds can further react to yield desired derivatives. Recently, vinyl magnesium bromide was reported to react with chloro complexes containing chromium or iron double bonds to silicon, to yield the l-metalla-2-sila-l,3-diene compounds (115, equation 34), which can potentially be used to functionalize silicon polymers in a desired fashion121. 

During the past decade, however, significant advances have been made in the preparation and chemistry of aliphatic organopolysilanes. A large number of silicon-silicon compounds of various types (peralkylated, silicon-functional, and carbon-functional) have been prepared, and mechanisms of some of their reactions elucidated. It is hoped that this review will demonstrate how the chemistry of aliphatic organopolysilanes is unique as well as similar to that of organomonosilanes. 

As mentioned previously, photocycloaddition reactions are a useful method for obtaining fullerene derivatives fused directly to heterocycles. Such compounds have attracted much interest because they might have interesting properties, e.g., amino acid fullerene derivatives as biologically active compounds or pyrrolidino-fullerenes as key precursors for a great number of fullerenes donor-acceptor bridged dyads and triads. Fullerenes functionalized with silicon compounds are of great interest in materials science. The synthesis of these compounds will be described in this section. 

Kami M, Apeloig Y, Knapp J, Schleyer PvR (2001) Chemistry of organic silicon compounds 3 1 (Patai series Rappaport Z (ed) The chemistry of functional groups. Wiley, New York)... 

Silicon compounds with both silicon-halogen and carbon-halogen bonds can react using both these functions an interesting example is the synthesis of the ferrasilacyclopentane (I) (.132) ... 

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