Silanols structural studies

The condensation of silanols in solution or with surfaces has not been as extensively studied and therefore is less well understood. The limitation until recently has been the lack of suitable analytical methods necessary to monitor in real time the many condensation products that form when di- or trifunctional silanols are used as substrates. With the advent of high-field wSi-NMR techniques, this limitation has been overcome and recent studies have provided insights into the effects of silanol structure, catalysts, solvent, pH, and temperature on the reaction rates and mechanisms. Analysis of the available data has indicated that the base catalyzed condensation of silanols proceeds by a rapid deprotonation of the silanol, followed by slow attack of the resulting silanolate on another silanol molecule. By analogy with the base catalyzed hydrolysis mechanism, this probably occurs by an SN2 -Si or SN2 -Si type mechanism with a pentavalent intermediate. The acid catalyzed condensation of silanols most likely proceeds by rapid protonation of the silanol followed by slow attack on a neutral molecule by an SN2-Si type mechanism. 

The increasing tendency of silanols to condense as the number of OH groups on a particular silicon increases means that relatively few silanetriols have been isolated and even fewer structurally characterized. A wide range of substituted arylsilanetriols have been prepared (102), but none have been studied by x-ray crystallography. The first silanetriol to be structurally characterized was c-C6HuSi(OH)3, which has a sheet structure comprising double layers of molecules joined in a... 

---