Compounds containing B-O-X bonds (X=Si, Ge, Sn, Pb) part 5. Synthesis of chain borosilicates containing B : Si ratios of 2 : 1, 2 : 2, 2 : 3 and 2 : 4. Crystal structure of (O-CMe2CH2CHMe-O-B-O)(2)SiBu2lt

Twelve borosilicates with the general formula O-Y-O-B-O-(SiPh2O)(n)-Br-O-Y- O (where n = 1, 2, 3 or 4; Y = one of the organic groups CMe2CMe2, CMe2CH2C HMe, CMe2CH2CMe2 or CHPr'CMe2CH2) were prepared. Three synthetic routes wer e investigated, including a one-pot self-assembly reaction of two equivalen ts each of boric acid, silanediol and organic diol. The probable sequence f or this reaction is discussed. The borosilicates were either solids or visc ous liquids and were colourless. They formed cyclosiloxane species when the rmally decomposed or reacted with either water or potassium trimethylsilano late. They were unreactive to triethylamine, di-iso-propylamine, pyridine o r ethylenediamine. The di-tert-butyl species (O-CMe2CH2CHMe-O-B-O)(2)SiBu2t was prepared and structurally characterised using X-ray techniques. The pa rameters associated with the B-O-Si bonds were a B-O-Si angle of 141.5(2)de grees and B-O and Si-O distances of 1.360(4) and 1.625(2) Angstrom, respect ively. (C) 1999 Elsevier Science Ltd. All rights reserved.