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Potassium 1-N,N-Dialkylamino-2,2-bis(trimethylsilyl)-2-Silenolates: Heavy Enolates with Remarkable Stability
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry, Organic Chemistry.
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Identifiers
URN: urn:nbn:se:uu:diva-92335OAI: oai:DiVA.org:uu-92335DiVA: diva2:165373
Available from: 2004-11-03 Created: 2004-11-03 Last updated: 2010-01-13Bibliographically approved
In thesis
1. Synthesis and Reactivity Studies of Zwitterionic Silenes and 2-Silenolates
Open this publication in new window or tab >>Synthesis and Reactivity Studies of Zwitterionic Silenes and 2-Silenolates
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis describes synthesis and reactivity studies of 2-amino-2-siloxysilenes and 2-silenolates, species that are strongly influenced by reversed Si=C bond polarization, i.e. an Siδ-=Cδ+ polarization as compared to the natural Siδ+=Cδ- polarization. Because of the reversed polarization, the 2-amino-2-siloxysilenes are zwitterions and the 2-silenolates are predominantly described by the resonance structure with the negative charge at Si.

Transient zwitterionic 2-amino-2-siloxysilenes are formed thermolytically from carbamylpolysilanes (tris(trimethylsilyl)silylamides) and trapped with 1,3-dienes in nearly quantitative yields. These silenes have structure and reactivity characteristics that differ from earlier studied Si=C bonded compounds. They are thermodynamically stable toward dimerization and react with 1,3-dienes to give exclusively [4+2] cycloadducts. Their reactions with 1,3-dienes proceed in accordance with inverse electron demand (IED) Diels-Alder reactions which is explained by the electron-rich nature of these silenes. The 2-amino-2-siloxysilenes are also less reactive toward alcohols than earlier silenes. Hence, alcohols do not react with 2-amino-2-siloxysilenes but with the silene precursor, the carbamylpolysilanes, leading to alkoxysilanes in high yields. The latter reaction represents a novel base-free synthetic protocol for protection of primary and secondary alcohols with the fluoride resistant but photolabile tris(trimethylsilyl)silyl group.

Another class of formally Si=C bonded compounds, metal 2-silenolates, has been formed in high yields using a novel facile method. Reaction of acyl- and carbamylpolysilanes with potassium tert-butoxide in tetrahydrofurane gives potassium 2-silenolates. The potassium 2-silenolates are stable at room temperature, in contrast to earlier lithium 2-silenolates that degrade rapidly at ambient temperature. The first crystallisable complex of a 2-silenolate was formed and characterized by X-ray crystallography. This 2-silenolate has a pyramidal central Si (ΣSi = 317.8°), and an Si-C single rather than Si=C double bond (r(SiC) = 1.926 Å). The potassium 2-silenolates give exclusively Si alkylated products with alkyl halides and only [4+2] cycloadducts with 1,3-dienes.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 60 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 1034
Keyword
Organic chemistry, Silicon, Zwitterionic Silene, 2-Silenolate, Diels-Alder Reaction, Silacyclohexene, X-ray Crystallography, Organisk kemi
National Category
Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-4650 (URN)91-554-6080-1 (ISBN)
Public defence
2004-11-26, B41, BMC, Husargatan 3, Uppsala, 13:15
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Available from: 2004-11-03 Created: 2004-11-03Bibliographically approved

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