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Synthesis, structures, and stereodynamic behavior of novel pentacoordinate fluorosilanes: fluorosilyl derivatives of proline

Nikolin, Alexei A.; Kramarova, Evgeniya P.; Shipov, Aleksander G.; Baukov, Yuri I.; Negrebetsky, Vadim V.; Korlyukov, Alexander A.; Arkhipov, Dmitry E.; Bowden, Allen; Bylikin, Sergey. Yu; Bassindale, Alan R. and Taylor, Peter G. (2012). Synthesis, structures, and stereodynamic behavior of novel pentacoordinate fluorosilanes: fluorosilyl derivatives of proline. Organometallics, 31(14) pp. 4988–4997.

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The (O→Si)-chelate N'-(dimethylfluorosilylmethyl))-N'-methyl-N-(organosulfonyl)prolinamides RSO2-Pro-N(Me)CH2SiMe2F (2a-f, R = Me (a), Ph (b), 4-MeC6H4 (c), 4-ClC6H4 (d), 4-BrC6H4 (e), 4-NO2C6H4 (f)) were synthesized from the corresponding disiloxanes 1a-f using Et2O•BF3. 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 angstrom) that is 0.02-0.11 angstrom 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 SiMe2 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.

Item Type: Article
Copyright Holders: 2012 American Chemical Society
ISSN: 1520-6041
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM)
Faculty of Science, Technology, Engineering and Mathematics (STEM) > Life, Health and Chemical Sciences
Other Departments > Vice-Chancellor's Office
Other Departments
Interdisciplinary Research Centre: Biomedical Research Network (BRN)
Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
Item ID: 34655
Depositing User: Peter Taylor
Date Deposited: 24 Oct 2012 11:02
Last Modified: 30 Nov 2016 14:34
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