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Formation and Fundamental Properties of Potassium Germen-2-olates
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Potassium 1,1-bis(trimethylsilyl)germen-2-olates (2a - 2d) with different substituents at the carbon atom were generated in good yields through the treatment of the correspondingly substituted tris(trimethylsilyl)acyl- and tris(trimethylsilyl)carbamyl-germanes (1a - 1d) with potassium tert-butoxide at room temperature in dry THF. Comparisons between the 29Si and 13C NMR chemical shifts of the germenolates and the analogous silenolates (4a4d) were performed. The recorded 13C and 29Si NMR chemical shifts of the potassium germenolates were also compared to those obtained from GIAO-B3LYP/6-31+G(d)//B3LYP/LANL2DZp calculations. The chemical reactivities of potassium germenolates were compared with silenolates. In this regard, the reactions of 2a - 2d were performed with methyliodide at -40 oC and the germanium methylated products (5a - 5c) were obtained in yields of 54 - 77 %. The reactions of these germenolates with 1,3-butadiene at low temperatures, however, lead to polymerization of dienes (2,3-dimethyl-1,3-butadiene, isoprene, and 1,3-pentadiene) revealing a reactivity resemblance to aminosilenolates, species which in return are comparable to silyl anions in reactivity.

National Category
Organic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-169795OAI: oai:DiVA.org:uu-169795DiVA, id: diva2:507712
Available from: 2012-03-06 Created: 2012-03-06 Last updated: 2012-04-19
In thesis
1. Low-coordinate Organosilicon Chemistry: Fundamentals, Excursions Outside the Field, and Potential Applications
Open this publication in new window or tab >>Low-coordinate Organosilicon Chemistry: Fundamentals, Excursions Outside the Field, and Potential Applications
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis reports on unsaturated silicon compounds, as well as excursions from these into germanium chemistry, single molecule electronics, and silyl protective group chemistry. Both experimental and computational investigations were performed.

Potassium germenolates were synthesized through reactions of tris(timethylsilyl) substituted acyl- and carbamylgermanes with potassium tert-butoxide. The potassium germenolates calculated by density functional theory have pyramidal structures at the Ge atoms, similar to the Si in the corresponding potassium silenolates, indicating negative charge on germanium rather than on oxygen. Germenolates also display germyl anion-like reactivity instead of germene-like reactivity as they are alkylated at Ge and initiate anionic polymerization of dienes rather than form [4+2] cycloadducts. The NMR chemical shifts reveal more negative charge at Ge in germenolates than at Si in analogous silenolates.

Computations indicate that silabenzenes and silapyridines are reachable via [1,3]-silyl shifts from cyclic conjugated acylsilanes. Differently sized substituents were considered to prevent dimerizations, and 1-triisopropylsilyl-2-triisopropylsiloxy-6-tert-butylsilabenzene is a good synthetic target. Computations also show that silaphenolates are species with negative charge primarily localized at oxygen atom. Their planar structures, bond lengths, and NICS values reveal significant influence of aromaticity. Electrostatic repulsion should increase their stability, however, steric bulk is also important.

Furthermore, it was found computationally that [1,3]-silyl shift from an acylsilane to a silene can function as a molecular switch reaction. Conductance calculations support this proposition.  

Finally, tris(trimethylsilyl)silylmethaneamide (hypersilylamide) together with catalytic amounts of triflic acid were found to be efficient for protection of a range of alkyl and aryl alcohols and thiols in good to excellent yields. The protocol can be used to protect the less hindered OH group of a diol and has a broad functional group tolerance. A catalytic cycle is proposed. Hypersilyl protected alcohols and thiols are deprotected efficiently under photolytic conditions.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. p. 75
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 907
Keywords
organosilicon, silene, silaaromatics, silenolate, hypersilyl group, alcohol protection, molecular switch
National Category
Organic Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-169796 (URN)978-91-554-8296-1 (ISBN)
Public defence
2012-04-21, B7:101a, BMC, Husargatan 3, Uppsala, 13:30 (English)
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Supervisors
Available from: 2012-03-30 Created: 2012-03-06 Last updated: 2012-04-19Bibliographically approved

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