CONVERSION OF HYDROSILANES TO ALKOXYSILANES CATALYZED BY CP2TICL2/NORMAL-BULI

The combination of Cp2TiCl2 and (n)BuLi provides an effective catalyst for alcoholysis of the model silanes n-HexSiH3, PhMeSiH2, Ph2SiH2 and PhMe2SiH by ethanol, isopropanol, t-butyl alcohol and phenol. Increasing the steric bulk of the substituents on either the alcohol or the silane generally requires longer reaction periods and/or increasing temperature. All SiH bonds are converted to SiOEt groups by ethanol and a single SiH bond in secondary silanes and two SiH bonds in tertiary silanes are replaced by t-butyl alcohol. Diols including pinacol, 2,4-pentanediol and 2,5-hexanediol react with PhRSiH2 (R = Me, Ph) to give 1,3-dioxa-2-silacyclopentanes, -hexanes and -heptanes, respectively. Attempts to form caged structures by condensation of primary silanes and triols was unsuccessful. Hydrolysis of PhRSiH2 is promoted by Cp2TiCl2/(n)BuLi and the siloxane is produced in quantitative yield when R = Ph and a mixture of linear disiloxanes and trisiloxanes in addition to cyclopolysilanes are produced when R = Me. Other protic reagents including acids. mercaptans, amines and enolizable ketones did not react. The effects of reaction parameters-such as temperature. silane to catalyst ratio, solvent. transition metal and replacements for (n)BuLi were also determined.