cyclo-Boratrisiloxane and cyclo-diboratetrasiloxane derivatives and their reactions with amines: crystal and molecular structure of (p-BrC6H4BO)(2)(Ph2SiO)(2)

The new cyclo-diboratetrasiloxanes (RBO)(2)(R-2'SiO)(2) (R = p-BrC6H4, o-Me C6H4, m-NH2C6H4, m-NO2C6H4, Bu-n; R-2' = Ph-2, R = Ph, p-BrC6H4, m-NO2C6H4; R-2' = oct(n)/Me) and cyclo-boratrisiloxanes (RBO)(R-2'SiO)(2) (R = p-BrC6 H4, m-NH2C6H4; R-2' = Me-2, Ph/Me) were prepared in high yield by condensat ion reactions. cyclo-Diboratetrasiloxane amine adducts (1:1) were obtained for (PhBO)(2)(Ph2SiO)(2) with cyclohexylamine, triethylamine, piperidine, a nd isobutylamine and for (o-MeC6H4BO)(2)(Ph2SiO)(2) with morpholine; in con trast the cyclo-boratrisiloxanes were unreactive towards amines. The Lewis acidity of these borasiloxane rings was determined by the Gutmann's accepto r number (AN) method with well-defined ranges observed for the cyclo-dibora tetrasiloxanes (46-62) and the cyclo-boratrisiloxanes (22-28). The crystal and molecular structure of (p-BrC6H4BO)(2)(Ph2SiO)(2) is reported. New comp ounds were characterised by elemental analysis, m.p., H-1- and B-11-NMR, an d IR spectroscopy; solids were characterised by solid-state B-11 MAS-NMR sp ectroscopy (C) 2000 Elsevier Science S.A. All rights reserved.