Nucleophilic substitution at silicon

In silicon derivatives, X-ray studies of compound 27 were consistent with a covalently bonded trigonal bipyramidal molecule <2000CC565>. In addition, nucleophilic substitution at silicon for similar compounds was modeled either by NMR or X-ray techniques and both methods correlate in the calculation of % Si-O bond formation <2003JOM66, 2003JOM154>. 

Hydrolysis and condensation reactions of silanes may be considered in the broad category of nucleophilic substitutions at silicon. The common nomenclature for these reactions is SN.V-Si, where A represents the kinetic order or molecularity, Si indicates that silicon is the reaction center, and SN indicates that the reaction is a nucleophilic substitution. Nucleophilic reactions at silicon have been reviewed thoroughly and have been the subject of fundamental studies by several laboratories over the last three decades [33]. The literature is not as voluminous as the literature on the corresponding reactions at carbon. A general mechanistic view of these reactions has, however, emerged. There are many parallels to carbon-centered reaction mechanisms. One distinction from carbon-centered reactions is clearly apparent. Silicon is able to form relatively stable higher coordinated (pentavalent) intermediates carbon is not [33]. 

In this review we have chosen to limit the scope to nucleophilic substitution at silicon. A short overview is given of material covered in detail in our previous review in The Chemistry of Organic Silicon Compounds 1, with recent advances covered in greater depth. 

Recently, the stereochemistry of nucleophilic substitution at silicon has been reviewed by Holmes2, and the role of pentacoordinate silicon compounds as reaction intermediates has been reviewed by Corriu and coworkers3. 

Nucleophilic substitution at silicon has frequently been found to be catalysed by the presence of other nucleophiles. Corriu and coworkers have found that the hydrolysis of... 

FIGURE 20. A map representing the progress along a reaction coordinate for nucleophilic substitution at silicon in solution, for a series of substituted silylpyridones. Derived from 29Si and 13C chemical shifts104,138. Reproduced from Reference 138 by permission of The Royal Society of Chemistry... 

Disilacyclobutanes can be functionalized by electrophilic or nucleophilic substitution at silicon, depending on the nature of the substituents. Alkoxy groups may be replaced by halogens in the presence of a Lewis acid, for example, by FeCl3 (Equation 16) <1997PSA3193, 2003JOM272>. 

Nucleophilic substitution at silicon in l,3-dichloro-l,3-disilacyclobutanes by Grignard reagents allows the introduction of alkyl groups onto the ring (Equation 18) <1997PSA3193>. 

Occasionally, it can be useful to run this reaction in reverse, generating the lithium enolate from the silyl enol ether. This can be done with methyllithium, which takes part in nucleophilic substitution at silicon to generate the lithium enolate plus tetramethylsilane. The reason why you might want to carry out this seemingly rather pointless transformation will become clear in Chapters 26 and 27. 

The aldehyde is formed immediately. What happens to the other product illustrates again just how easy nucleophilic substitution at silicon can be. Two of these compounds combine together to give a disilyl ether, called a disiloxane. 

We have reported a new technique for mapping the progress of nucleophilic substitution at silicon, through a pentacoordinate silicon [7]. The method requires the synthesis of a series of model compounds, each of which corresponds to a point on the reaction profile. The first example was the pyridone series represented in Scheme 5. 

Scheme 5. A model system for mapping nucleophilic substitution at silicon in solution...

Pathways for Nucleophilic Substitution at Silicon. A Molecular Orbital Approach. ... 

Investigations of Nucleophilic Substitution at Silicon An Unprecedented Equilibrium between an Ionic and a Covalent Chlorosilane... 

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