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)3SiCl (1), (t‐BuO)2SiCl2 (2), and [(t‐BuO)2SiCl]2O (3) were prepared by the reaction of SiCl4 or (Cl3Si)2O with t‐BuOK. Subsequent hydrolysis afforded the tert‐butoxysilanols (t‐BuO)3SiOH (4), (t‐BuO)2Si(OH)2 (5), HO[(t‐BuO)2SiO]2H (6) in high yields. The controlled condensation of 2 and 5 provided HO[(t‐BuO)2SiO]3H (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 29Si 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.