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Issue 2, 2017
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Electronic nature of zwitterionic alkali metal methanides, silanides and germanides – a combined experimental and computational approach

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Abstract

Zwitterionic group 14 complexes of the alkali metals of formula [C(SiMe2OCH2CH2OMe)3M], (M-1), [Si(SiMe2OCH2CH2OMe)3M], (M-2), [Ge(SiMe2OCH2CH2OMe)3M], (M-3), where M = Li, Na or K, have been prepared, structurally characterized and their electronic nature was investigated by computational methods. Zwitterions M-2 and M-3 were synthesized via reactions of [Si(SiMe2OCH2CH2OMe)4] (2) and [Ge(SiMe2OCH2CH2OMe)4] (3) with MOBut (M = Li, Na or K), resp., in almost quantitative yields, while M-1 were prepared from deprotonation of [HC(SiMe2OCH2CH2OMe)3] (1) with LiBut, NaCH2Ph and KCH2Ph, resp. X-ray crystallographic studies and DFT calculations in the gas-phase, including calculations of the NPA charges confirm the zwitterionic nature of these compounds, with the alkali metal cations being rigidly locked and charge separated from the anion by the internal OCH2CH2OMe donor groups. Natural bond orbital (NBO) analysis and the second order perturbation theory analysis of the NBOs reveal significant hyperconjugative interactions in M-1–M-3, primarily between the lone pair and the antibonding Si–O orbitals, the extent of which decreases in the order M-1 > M-2 > M-3. The experimental basicities and the calculated gas-phase basicities of M-1–M-3 reveal the zwitterionic alkali metal methanides M-1 to be significantly stronger bases than the analogous silanides M-2 and germanium M-3.

Graphical abstract: Electronic nature of zwitterionic alkali metal methanides, silanides and germanides – a combined experimental and computational approach

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Publication details

The article was received on 31 May 2016, accepted on 06 Oct 2016 and first published on 07 Oct 2016


Article type: Edge Article
DOI: 10.1039/C6SC02390H
Citation: Chem. Sci., 2017,8, 1316-1328
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    Electronic nature of zwitterionic alkali metal methanides, silanides and germanides – a combined experimental and computational approach

    H. Li, A. J. A. Aquino, D. B. Cordes, W. L. Hase and C. Krempner, Chem. Sci., 2017, 8, 1316
    DOI: 10.1039/C6SC02390H

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