| Project/Area Number |
08045021
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| Research Category |
Grant-in-Aid for international Scientific Research
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| Allocation Type | Single-year Grants |
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| Section | University-to-University Cooperative Research |
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| Research Field |
機能・物性・材料
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| Research Institution | University of Tsukuba |
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Principal Investigator |
ANDO Wataru University of Tsukuba, Chemistry, Professor, 化学系, 教授 (30008429)
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| Co-Investigator(Kenkyū-buntansha) |
ドミトリ ブラホツィホト テクニオン, イスラエル工業大学・理学部, 助教授
イイザック アペログ テクニオン, イスラエル工業大学・理学部, 教授
KABE Yoshio University of Tsukuba, Chemistry, Assistant prof., 化学系, 講師 (40214506)
KIKUCHI Osamu University of Tsukuba, Chemistry, Professor, 化学系, 教授 (30015771)
YITZHAK Apeloig Technion-Israel Institute of Technology, Professor
DMITRY Bravo-Zhivotovski Technion-Israel Institute of Technology, Assosiate Professor
ブラホツィホトフスキー ドミトリ テクニオン, イスラエル工業大学・理学部, 助教授
アペログ イイザック テクニオン, イスラエル工業大学・理学部, 教授
陳 祥 筑波大学, 化学系, 助手 (70261758)
イイザック アペローグ テクニオン, イスラエル工業大学・理学部, 教授
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| Project Period (FY) |
1996 – 1997
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| Project Status |
Completed (Fiscal Year 1997)
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| Budget Amount *help |
¥4,000,000 (Direct Cost: ¥4,000,000)
Fiscal Year 1997: ¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1996: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Keywords | disilaanthracene / relative stability / Dewar-silabenzene / silaprismane / bissilayclopropenes / molecular orbital calculations / シラベンゼン / モノシラシクロプロペニル / シラシクロブタジエン / 分子軌道計算(HF / 3-21G^*) / 熱異性化 / ケイ素ジアニオン / 架橋リチオ体 / ケイ素芳香族体 |
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| Research Abstract |
The replacement of two carbon atoms by two silicon atoms reduces the energy gap by influence all three factors. First, silasubstituted benzenes are estimated to be less aromatic than benzene. Second, silicon can easily adopt angles of around 90ﾟ while C prefers essentially tetrahedral angles. Third, Si prefers to form Si-C and Si-Si single bonds over Si=C or Si=Si pi bonds. The calculations reveal that 1,4-disilabenzene is more stable than its Dewar form but the enthalpy difference is much small than for benzene. The B3LYP calculations show that 9,10-disilaanthracene (SA) is less stable than the Dewar isomer by -l2.1 kcal/mol. The change in relative stability of the aromatic vs.the Dewar isomer is similar on going from benzene to anthracene in the all carbon system (20kca1/mol) and in the disila-systems (26 kcal/mol). SA possesses C2h-symmetry, in which the central disilabenzene ring adopts a slightly nonplanar chair-type structure (with a Si-C-C-Si dihedral angle of 5.5ﾟ). This is con
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sistent with the smaller degree of aromaticity in this ring. The planar form of SA (i.e., possessing D2h -symmetry) is a transition state that connects the two isomeric C2h-minima, but it is by only 0.02kcal/mol higher in energy, suggesting that SA is essentially a planar molecule. We underlined the similarities between silicon and carbon. The formation of disilabenzene as well as Dewar-silabenzene, silabenzvalene, and silaprismane could be obtained from corresponding bissilayclopropenes. Thermolysis of 3,3'-biscyclopropenyl (BC) at l50ﾟC afforded the rearranged product benzvalene (82%). It could be considered the initial formation of an intermediate either Dewar benzene and 1,4-disilabenezene and their subsequent isomerization to benzvalene.To evaluate the stabilities of BC,the relative energies of the corresponding valence isomers were determined by 6-3lG^<**> molecular orbital calculations. As a result, the benzvalene and the Dewar benzene have similar energy levels and are slightly less stable than 1,4-disilabenzene. Since large basis sets and inclusion of electron correlation generally tend to favor tricyclic over bicyclic or monocyclic geometries may have quite similar energies ; the stability order may even be reversed. Actually, methyl substituted BC arranged to Dewar-silabenzene. However, disilabenzene was not isolated under the reaction conditions. SA dimer prepared from the reaction of dihydro-9,10-disilaanthracene with lithium was treated with excess lithium or potassium resulted in formation of the 9,10-alkali-9,10-disilaanthracene. On treatment with a, omega-dichloropolysilanes, the dianion was converted into the corresponding cyclic silicon compounds. Oxidation of dianion with electron acceptors gave the SA dimer and in the presence of diphenylacetylene gave [2+4] addition product. The results show that SA could be generated from dianion oxidation process. Less
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