2005 Fiscal Year Final Research Report Summary
Studies on Properties of Long Ladder Polysilanes with Double Helix Structures
| Project/Area Number |
16550029
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Organic chemistry
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| Research Institution | Gunma University |
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Principal Investigator |
KYUSIN Soichiro Gunma University, Department of Nano-Material Systems, Professor, 大学院・工学研究科, 教授 (40195392)
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| Project Period (FY) |
2004 – 2005
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| Keywords | ladder polysilane / double helix structure / silyl dianion |
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| Research Abstract |
In this research project, long ladder polysilanes were synthesized, and their structures and properties were studied. Also, the dianion of the tricyclic ladder polysilane was isolated, and its structure and reactions were studied.
The hexa- to octacyclic ladder polysilanes were synthesized by the coupling of 1,1,4,4-tetrachlorohexaisopropyl-tetrasilane and 1,1,2,2-tetrachlorodiisopropyldisilane with lithium. The X-ray analysis showed that the silicon skeletons of these compounds have double helix structures, and the twist angles between the terminal silicon-silicon rungs are 96.2 and 101.1°(hexacyclic), 119.6°(heptacyclic), and 128.5°(octacyclic). As the number of cyclotetrasilane rings of the ladder polysilanes increases, the lowest energy absorption maximum in the UV-visible spectra shifts bathochromically, and the oxidation potential decreases. Molecular orbital calculations showed that these electronic properties are explained by the destabilization of the energy level of the highest occupied molecular orbital (HOMO) and the stabilization of the energy level of the lowest unoccupied molecular orbital (LUMO).
By the reduction of the tricyclic ladder polysilane with potassium in the presence of 18-crown-6, the silicon-silicon bond at the 1,2-positions of the tricyclic ladder polysilane was cleaved to give bis(2-potassiohexaisopropylcyclotetrasilanyl). The X-ray analysis showed that the inversion around the silicon atoms at the 1,2-positions took place during the reduction, and two potassium ions were incorporated into 18-crown-6. The reactions of this dianion with dimethyldichlorosilane or trimethylchlorosilane gave novel polysilanes with tricyclo[5.2.0.0^<2,5>]nonasilane and bis(cyclotetrasilanyl) skeletons.
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