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A Computational Investigation of the Retrocyclization Reaction of Silacyclo-but-2-enes to 1-silabuta-1,3-dienes: Focus on the effect of the substituents
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
2007 (English)In: Journal of Molecular Structure: THEOCHEM, ISSN 0166-1280, Vol. 811, no 1-3, 153-160 p.Article in journal (Refereed) Published
Abstract [en]

Substituent effects on the reaction profile of the thermal retrocyclization reaction of silacyclobut-2-enes to 1-silabuta-1,3-dienes were studied using B3LYP hybrid density functional theory as well as CCSD and CCSD(T) ab initio calculations. Several different substituents (–CF3, –SiH3, –CN, –OCH3, –OH, and –NH2) were used to investigate their effects on the relative energies of the transition states of the retrocyclization reaction as well as of the 1-silabutadiene products. It was found that π-donor groups at the 4-position greatly reduce the energy barriers, and also stabilize the 1-silabutadienes relative to the silacyclobut-2-enes. Silyl substituents at the silicon atom will facilitate the reaction when compared to alkyl substituents. The results thus indicate that the ring-opening reaction of 4,4-disubstituted 1,1-disilylsilacyclobut-2-enes with π-donor substituents are particularly suitable entries for formation of 1-silabutadienes of low relative energy.

Place, publisher, year, edition, pages
2007. Vol. 811, no 1-3, 153-160 p.
Keyword [en]
Silicon, Retrocyclization, Density functional theory, Ab initio, Silene, Silacyclobut-2-ene, 1-Silabutadiene
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-97588DOI: 10.1016/j.theochem.2007.02.024ISI: 000247053500018OAI: oai:DiVA.org:uu-97588DiVA: diva2:172588
Available from: 2008-10-03 Created: 2008-10-03 Last updated: 2011-02-01Bibliographically approved
In thesis
1. Lowcoordinated Silicon and Hypercoordinated Carbon: Structure and Stability of Silicon Analogs of Alkenes and Carbon Analogs of Silicates
Open this publication in new window or tab >>Lowcoordinated Silicon and Hypercoordinated Carbon: Structure and Stability of Silicon Analogs of Alkenes and Carbon Analogs of Silicates
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Quantum chemical studies on lowcoordinated group 14-16 compounds have been performed. This thesis focuses particularly on silenes influenced by reverse Siδ-=Cδ+ bond polarization. Hypercoordinated carbon compounds are also studied.

The geometries from calculations with several common computationally inexpensive methods have been tested against high level CCSD/cc-pVTZ geometries for a series of substituted silenes. Hybrid HF/DFT methods performed best among the inexpensive methods tested for silenes.

Heavy alkenes strongly influenced by reverse polarization are found to have less exothermic dimerization energies for both head-to-head and head-to-tail dimerizations, and to have higher activation energies for water addition than naturally polarized heavy alkenes.

We also investigated solvated lithium, magnesium and potassium silenolates and found that lithium and magnesium ions coordinate preferably to O, giving their SiC bond some double bond character.

Reverse polarized 2-siloxy-, 2-thiosiloxy-, and 2-(N-sila-N-methyl)-silenes could according to calculations be formed thermolytically from the corresponding tetrasilanes as transient species. It was, however, found that silenes highly influenced by π-conjugative reverse polarization have low barriers for the back-reaction, and thus these silenes are more difficult to form as stable species than naturally polarized silenes.

It is also found that conjugated 1-siladienes, formed by electrocyclic ring-opening of 1-silacyclobut-2-enes, which are highly influenced by π-conjugative reverse polarization, have higher barriers for electrocyclization back to starting material than naturally polarized 1-siladienes.

It is found that CHe54+, CHe64+, CNe54+, and CNe64+ are the closest carbon analogs of SiH5-, SiH62-, SiF5- and SiF62-, respectively. However, due to their exothermic dissociation reaction, these very high-lying local minima will be impossible to reach experimentally.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 85 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 557
Keyword
silenes, zwitterionic silenes, silenolates, reverse polarization, natural resonance theory, hypervalent carbon, hypercoordinated carbon, thermolysis, lowcoordinated silicon
National Category
Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-9298 (URN)978-91-554-7294-8 (ISBN)
Public defence
2008-10-25, C8:301, BMC, Husargatan 3 753 21, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2008-10-03 Created: 2008-10-03 Last updated: 2009-03-26Bibliographically approved

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