Nikolin A.A.,rogov Russian National Investigated Medical University |
Kramarova E.P.,rogov Russian National Investigated Medical University |
Shipov A.G.,rogov Russian National Investigated Medical University |
Baukov Y.I.,rogov Russian National Investigated Medical University |
And 7 more authors.
The (O→Si)-chelate N′-(dimethylfluorosilylmethyl))-N′- methyl-N-(organosulfonyl)prolinamides RSO 2-Pro-N(Me)CH 2SiMe 2F (2a-f, R = Me (a), Ph (b), 4-MeC 6H 4 (c), 4-ClC 6H 4 (d), 4-BrC 6H 4 (e), 4-NO 2C 6H 4 (f)) were synthesized from the corresponding disiloxanes 1a-f using Et 2O• BF 3. According to the NMR and IR data, the extent of dimerization of fluorosilanes 2a-f in solution is negligible, while the O→Si coordination in solution is weaker than that in the solid state. Comparative CP/MAS NMR and X-ray diffraction studies revealed that in solution the coordination Si-O bond length varies in a narrow range (2.22-2.24 Å) that is 0.02-0.11 Å longer than in the crystalline state. Dynamic NMR (DNMR) studies of the fluorides revealed a fine structure of the 19F signals in the 0-20 °C temperature range, which was related to the structural features of the coordination set in these complexes. The temperature dependence of the SiMe 2 signals in the 1H DNMR spectra was attributed to a permutational isomerization process involving a positional exchange of equatorial ligands. The narrow range of activational barriers of the process (23-24 kcal mol -1 and more) and high negative values of the entropy of activation are similar to those observed earlier for Si-substituted N-(dimethylsilylmethyl) and N-(methylphenylsilylmethyl) amides and lactams, which suggests similar permutational processes in all cases. Gas-phase quantum chemical studies demonstrate that the solvation of F - reduces the activation barrier. © 2012 American Chemical Society. Source