Nucleophilic substitution, hypervalent silicon

The kinetics of nucleophilic substitution at the silicon atom assisted by uncharged nucleophiles have been studied by Corriu et at. (248-251). Hydrolysis of triorganochlorosilanes induced with HMPA, DMSO, and DMF was used as the model. The reaction proceeded according to the third-order kinetic law, first order with respect to the nucleophile, the silane, and the silylation substrate. Very low values of activation enthalpy and high negative entropy of activation were observed (Table VI). These results were taken as evidence for the intermediacy of silicon hypervalent species (249,251) however, they are also perfectly consistent with... 

Silicon compounds with coordination number larger than four are the object of many studies first with respect to their application as catalysts in organic and inorganic syntheses and second as starting materials for the preparation of a broad variety of organosilicon compounds [1]. Additionally, hypervalent silicon hydride compounds can successfully be used as model compounds to study, for instance, the mechanism of nucleophilic substitution reactions, which is of great interest since the silicon atom is able to easily extend its coordination number [1]. Moreover, hypervalent silanes are suitable as starting materials for the synthesis and stabilization of low-valent silanediyl transition metal complexes [2-5]. 

In this context, the existence of stable penta- and hexacoordinate silicon derivatives and their structure have elicited considerable interest. Isomerization processes of these compounds are also of importance, since penta- or hexacoor-dinate intermediates are implicated in the substitution and racemization of tetracoordinate silicon derivatives. For all these reasons, we include here (i) some available structural data for hypervalent silicon compounds (the review is not intended to be exhaustive), (ii) recent reports concerning the nucleophilically induced substitution and racemization reactions at silicon, and (ii) a criti-... 

Silicon-based Polymeric Materials Mechanistic Organosilicon Chemistry (a) Gas Phase and Photochemical Reactions (b) Hypervalent Silicon, Nucleophilic Substitution, and Biotransformations Structural Organosilicon Chemistry and New Organosilicon Compounds Organic Synthesis using Siiicon. 

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