tert-butoxysilanols as model compounds for labile key intermediates of the sol-gel process:: crystal and molecular structures of (t-BuO)3SiOH and HO[(t-BuO)2SiO]2H

The tert-butoxychlorosilanes (t-BuO)(3)SiCl (1), (t-BUO)(2)SiCl2 (2), and [(t-BuO)(2)SiCl](2)O (3) were prepared by the reaction of SiCl4 or (C13Si)(2)O With t-BuOK. Subsequent hydrolysis afforded the tert- butoxysilanols (t-BuO)(3)SiOH (4), (t-BuO)(2)Si(OH)(2) (5), HO[(t-BuO)(2)SiO](2)H (6) in high yields. The controlled condensation of 2 and 5 provided HO[(t-BuO)(2)SiO](3)H (7) in reasonable yields. The tendency of 4-7 to undergo self-condensation is small, thus enabling their characterization in solution and in the solid state by Si-29 NMR spectroscopy, IR spectroscopy and electrospray mass spectrometry, and in the case of 4 and 6 also by X-ray diffraction. The key feature of the crystal structures is the incorporation of tert-butoxy groups into the hydrogen bonding. The results obtained are discussed in relation to the sol-gel process. Copyright (C) 2002 John Wiley Sons, Ltd.