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The [1,3]-Si→O Silyl Shift from a Nonconducting Acylsilane to a Conducting Brook-Silene as Basis for a Molecular Switch
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

By usage of density functional theory (DFT) calculations we explored if the [1,3]-silyl shift leading from an acylsilane with two p-conjugated substituents to a silene (a Si=C double bonded compound) can be used as a basis for a molecular conductance switch. In such a switch, the acylsilane, with a tetrahedral saturated silicon atom disrupting the conjugation through the molecule, acts as the OFF state, whereas the silene with a conjugated path running through the complete molecule represents the ON state. Our requirements are (i) the silenes should be slightly higher in relative energy than the acylsilane so as to promote a thermal backrearragment, (ii) the barrier for the backtransfer of the silyl group should be 25-30 kcal/mol, (iii) the ON/OFF conductance ratio should be high, and (iv) the switch should be realistic. According to our calculations using non-equilibrium Green’s function theory, a 1,2-bis(4-thiophenylethynyl)silene has a conductance which is 270 times higher than that of the corresponding acylsilane at zero bias voltage. However, at a voltage of +1 V the ON/OFF ratio decreases to ~40.

National Category
Organic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-169782OAI: oai:DiVA.org:uu-169782DiVA: diva2:507687
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. 75 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 907
Keyword
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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Löfås, HenrikGrigoriev, AntonAhuja, Rajeev

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