Abstract
A kinetic investigation of the base-catalyzed decomposition of pentaphenyldisilanecarboxylic acid ( 1) and pentaphenyldisilanol ( 2) in ethanol/water media is reported. The solvolysis of the SiSi bond in 2, which also is formed on the base-catalyzed decarbonylation of 1, proceeds by concurrent first-order and second-order processes. At low base concentrations where the first-order process predominates, the intermediate, triphenylsilane ( 3), has been isolated. Solvent isotope effects and activation parameters have been determined. Mechanisms are proposed for the two kinetically distinguishable processes for SiSi bond cleavage in which the pentaphenyldisilanolate ion undergoes either an internal nucleophilic displacement reaction or nucleophilic attack at Si by base in the rate-determining step. A general mechanistic approach for the cleavage of Si bonds in polysilanes by aqueous-alcoholic base is proposed in which polysilanolate ions are formed by nucleophilic attack by base at Si which undergo internal nucleophilic attack resulting in cleavage of the SiSi bond adjacent to the anionic termini. Subsequently, polysilanolate ions are regenerated in which the number of Si atoms is reduced by one.
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