Strong Intramolecular Si−N Interactions in the Chlorosilanes Cl3−nHnSiOCH2CH2NMe2 (n = 1−3)

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• 作者：Michael Hagemann ; Andreas Mix ; Raphael J. F. Berger ; Tania Pape ; Norbert W. Mitzel
• 刊名：Inorganic Chemistry
• 出版年：2008
• 出版时间：November 17, 2008
• 年：2008
• 卷：47
• 期：22
• 页码：10554-10564
• 全文大小：401K
• 年卷期：v.47,no.22(November 17, 2008)
• ISSN：1520-510X

文摘

The compounds Cl₃SiOCH₂CH₂NMe₂ (1) and Cl₂HSiOCH₂CH₂NMe₂ (2) were prepared by reactions of lithium 2-(dimethylamino)ethanolate with SiCl₄ and HSiCl₃. The analogous reaction with H₂SiCl₂ gave ClH₂SiOCH₂CH₂NMe₂ (3), but only in a mixture with Cl₂HSiOCH₂CH₂NMe₂ (2), from which it could not be separated. All compounds were characterized by IR and NMR (¹H, ¹³C, ²⁹Si) spectroscopy, 1 and 2 by elemental analyses and by determination of their crystal structures. Cl₃SiOCH₂CH₂NMe₂ (1) and Cl₂HSiOCH₂CH₂NMe₂ (2) crystallize as monomeric ring compounds with pentacoordinate silicon atoms participating in intramolecular Si−N bonds [2.060(2) Å (1), 2.037(2) Å (2)]. The dative bonds in 1 and 2 between the silicon and nitrogen atoms could also be proven to exist at low temperatures in solution in ¹H,²⁹Si-HMBC-NMR experiments by detection of the scalar coupling between the ²⁹Si and the protons of the NCH₂ and NCH₃ groups. A function describing the chemical shift δ_exp²⁹Si dependent on the chemical shifts of the individual equilibrium components, the temperature, and the free enthalpy of reaction was worked out and fitted to the experimental VT-NMR data of 1 and 2. This provided values of the free reaction enthalpies of ΔG = −28.8 ± 3.9 kJ·mol⁻¹ for 1 and ΔG = −22.3 ± 0.4 kJ·mol⁻¹ for 2 and estimates for the chemical shifts of open-chain (index o) and ring conformers (index r) for 1 of δ_r = −94 ± 2 ppm and δ_o = −36 ± 5 ppm and for 2 of δ_r = −82 ± 1 ppm and δ_o = −33 ± 4 ppm. The value of δ_r for 1 is very close to that obtained from a solid-state ²⁹Si MAS NMR spectrum. Quantumchemical calculations (up to MP2/TZVPP) gave largely differing geometries for 1 (with a Si···N distance of 3.072 Å), but well reproduced the geometry of 2. These differences are due to Cl···H and Cl···C repulsions and solid state effects, which can be modeled by conductor-like screening model calculations and also rationalized in terms of the topology of the electron density, which was analyzed in terms of the quantum theory of atoms in molecules.