New mechanisms for the base-catalyzed cleavage of Si-Si bonds in organopolysilanes: the base-catalyzed solvolysis of pentaphenyldisilanecarboxylic acid and pentaphenyldisilanol in ethanol/water media

Article abstract of DOI:10.1016/0022-328X(88)89075-2

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 Si-Si 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 Si-Si 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-Si bonds in polysilanes by aqueous-alcoholic base is proposed in which polysilonate ions are formed by nucleophilic attack by base at Si which undergo internal nucleophilic attack resulting in cleavage of the Si-Si bond adjacent to the anionic termini.Subsequently, polysilanolate ions are regenerated in which the number of Si atoms is reduced by one.