| Abstrakt: |
The oximatosilanes H3SiON&z.dbd6;CMe2, ClH2SiON&z.dbd6;CMe2 and H2Si(ON&z.dbd6;CMe2)2 were prepared from the reaction of lithiated acetone oxime with bromosilane and dichlorosilane respectively. They have been characterised by NMR (1H, 13C, 15N, 17O and 29Si) and by gas-phase IR spectroscopy. The molecular structures of H3SiON&z.dbd6;CMe2 and H2Si(ON&z.dbd6;CMe2)2 have been determined by low-temperature X-ray crystallography. Small Si–O–N angles have been detected in these structures, which are indicative of the formation of weak secondary interactions of the β-donor–acceptor type between silicon and nitrogen atoms. Important geometrical parameters: H3SiON&z.dbd6;CMe2, Si–O 1.673(1), N–O 1.433(1) Å, Si–O–N 106.0(1)°, N&z.dbd6;C 1.273(2) Å; H2Si(ON&z.dbd6;CMe2)2, Si–O 1.657(1), 1.650(1), N–O 1.466(2), 1.447(2), N&z.dbd6;C 1.271(2), 1.266(2) Å, Si–O–N 102.5(1), 107.5(1)°. The geometries of H3SiON&z.dbd6;CMe2, FH2SiON&z.dbd6;CMe2 and ClH2SiON&z.dbd6;CMe2 were calculated by optimisations at the MP2/6-311G** level of theory. The Si–O–N angles in FH2SiON&z.dbd6;CMe2 and ClH2SiON&z.dbd6;CMe2 are predicted to be smaller than that in H3SiON&z.dbd6;CMe2. A natural bond orbital analysis describes the β-donor interaction as weak negative hyperconjugation lp(O)→σ*(SiO) and lp(O)→σ*(SiH). In general the β-donor bonds in oximatosilanes are found to be weaker than in the related hydroxyaminosilanes. |
