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Unsuccessful attempts to add alcohols to transient 2-amino-2-siloxy- silenes - leading to a new benign route for base-free alcohol protection
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry. (Henrik Ottosson)
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry. (Henrik Ottosson)
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry. (Henrik Ottosson)
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry. (Henrik Ottosson)
2010 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 39, no 39, 9379-9385 p.Article in journal (Refereed) Published
Abstract [en]

Thermolytic formation of transient   1,1-bis(trimethylsilyl)-2-dimethylamino-2-trimethylsiloxysilene (2)  from N,N-dimethyl(tris(trimethylsilyl) silyl) methaneamide (1) in presence of a series of alcohols was investigated. The products are,  however, not the expected alcohol-silene addition adducts but   silylethers formed in nearly quantitative yields. Thermolysis of 1 in   the presence of both alcohols (MeOH or iPrOH) and 1,3-dienes   (1,3-butadiene or 2,3-dimethyl-1,3-butadiene) gives   alkyl-tris(trimethylsilyl)silylethers and the [4+2] cycloadducts   between the silene and diene, which confirms the presence of 2 and that   it is unreactive towards alcohols. The observed silylethers are substitution adducts where the amide group of the silylamide is replaced by an alkoxy group, and the reaction time is reflected in the   steric bulk of the alcohol. Indeed, the formation of silylethers from   the reaction of alcohols with silylamide represents a new base-free   method for protection of alcohols. The protection reactions using 1   progresses at elevated temperatures, or alternatively, under acid   catalysis at ambient temperature, and similar protections can be   carried out with N-cyclohexyl(triphenylsilyl) methaneamide and N,   N-dimethyl(trimethylsilyl) methaneamide. The latter silylamide can be used under neutral conditions at room temperature. The only by-products  are formamides (N,N-dimethylformamide (DMF) or N-cyclohexylformamide), and the reactions can be performed without solvent. In addition to alcohols we also examined the method for protection of diols, thiols   and carboxylic acids,and also these reactions proceeded in high yields and with good selectivities.

Place, publisher, year, edition, pages
2010. Vol. 39, no 39, 9379-9385 p.
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-123086DOI: 10.1039/c0dt00323aISI: 000282220500030PubMedID: 20733993OAI: oai:DiVA.org:uu-123086DiVA: diva2:311808
Note
Uppdaterad från Manuskript till Artikel 20101201Available from: 2010-04-23 Created: 2010-04-23 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Organic Heavy Group 14 Element Compounds: A Study of Their Chemical Bonding Properties Directed Towards Applications as Molecular Wires and in Synthesis
Open this publication in new window or tab >>Organic Heavy Group 14 Element Compounds: A Study of Their Chemical Bonding Properties Directed Towards Applications as Molecular Wires and in Synthesis
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The research described herein includes synthesis, spectroscopy, and quantum chemical calculations with focus on the characteristic properties of compounds with bonds between carbon and the heavier Group 14 elements.

The chapters based on the first four papers concern σ- and σ/π-conjugated compounds, although the focus of the first paper is on ring strain of bicyclo[1.1.1]pentanes with C, Si, Ge or Sn at the bridgeheads. The relationship between calculated homodesmotic ring strain energies and through-space distances between the bridgehead atoms was evaluated, and it was found that replacing one of the methylene bridges with phospha-methyl gave both low strain and short through-space distance.

Two kinds of σ/π-interacting systems were analysed with the difference that the σ- and π-bonded segments were either allowed to rotate freely relative each other or frozen into a conformer with maximal σ/π-interaction. The freely rotating systems are star-shaped oligothiophenes linked by heavy alkane segments. Density functional theory (DFT) calculations of hole reorganization energies support the measured hole mobilites. In summary, longer central oligosilane linkages, when compared to shorter, facilitate intermolecular hole-transfer between oligothiophene units.

In 1,4-disilacyclohexa-2,5-dienes, the strength of the π- and pseudo-π interaction depends on the substituents at Si. Vapour phase UV absorption spectroscopy of 2,3,5,6-tetraethyl-1,1,4,4-tetrakis(trimethylsilyl)-1,4-disilacyclohexa-2,5-diene reveals a strong absorption at 273 nm (4.50 eV). Time-dependent DFT calculations further indicate that octastannylated 1,4-disilacyclohexa-2,5-diene has is lowest excited state at 384 nm (3.23 eV). The electronic, geometric and optical properties of substituted 1,4-disilacyclohexa-2,5-dienes were compared with those of the correspondingly substituted siloles. It was found that the lowest excitations of siloles are less tunable than those of 1,4-disilacyclohexa-2,5-dienes.

The final section concerns strongly reverse-polarised 2-amino-2-siloxysilenes formed thermally from carbamylpolysilanes, and their lack of reaction with alcohols. Instead, the carbamylsilane reacts with alcohols giving silyl ethers, leading to a new benign route for alcohol protection.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. 81 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 747
Keyword
Silicon, Group 14 Elements, Silenes, Conjugation, Chemical Bonding, Electronic Structure, Protecting Group Chemistry
National Category
Organic Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-123088 (URN)978-91-554-7820-9 (ISBN)
Public defence
2010-06-04, B42, Husargatan 3, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2010-05-11 Created: 2010-04-23 Last updated: 2010-05-18

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