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, CMe2CH2CHMe, CMe2CH2CMe2 or CHPr'CMe2CH2) were prepared. Three synthetic routes were investigated, including a one-pot self-assembly reaction of two equivalents each of boric acid, silanediol and organic diol. The probable sequence for this reaction is discussed. The borosilicates were either solids or viscous liquids and were colourless. They formed cyclosiloxane species when thermally decomposed or reacted with either water or potassium trimethylsilanolate. They were unreactive to triethylamine, di-iso-propylamine, pyridine or ethylenediamine. The di-tert-butyl species (O-CMe2CH2CHMe-O-B-O)(2)SiBu2t was prepared and structurally characterised using X-ray techniques. The parameters associated with the B-O-Si bonds were a B-O-Si angle of 141.5(2)degrees and B-O and Si-O distances of 1.360(4) and 1.625(2) Angstrom, respectively. (C) 1999 Elsevier Science Ltd. All rights reserved.