Unexpected Silaazetidine Formation in the Thermolysis of thf-Supported Silanimine Et2Si=N-SitBu3·thf

The chemical behavior of the silaoxine C22H34OSi3 and silaazetidine C25H43NSi4 towards CO2

When 4,4a-dihydro-3,3-dimethyl-1-phenyl-4,4-bis(trimethylsilyl)-3H-2-oxa-3-sila-naphthaline (silaoxine C22H34OSi3 (3); orthorhombic, space group Pna21, Z=4) was thermolized in a CO2 atmosphere, the corresponding oxasilacyclobutane (silaoxetane) 5 was quantitatively formed. The [2+2] cycloreversion of the silaoxetane 5 occurred at temperatures higher than 120°C to give exclusively Ph2C=C(SiMe3)2 and (Me2SiO) n . Single crystals of Ph2C=C(SiMe3)2 (6; monoclinic, space group C2/c, Z=8) were isolated from this reaction. When the azasilacyclobutane (silaazetidine) C25H43NSi4 (4; monoclinic, space group P21/n, Z=4) was reacted with an excess of CO2 at 100°C an unknown intermediate was formed along with the benzophenonimine Ph2C=N(SiMe3). The NMR resonances of this intermediate indicates the formation of the β-silalactone (silaoxetanone) C10H24O2Si3 (7). At temperatures higher than 120°C the silaoxetanone 7 decomposed to give (Me3Si)2C=C=O and (Me2SiO) n , respectively.