| Project/Area Number |
05640587
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Organic chemistry
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| Research Institution | Tohoku University |
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Principal Investigator |
KIRA Mitsuo TOHOKU UNIV., DEPT.CHEM., ASSOC.PROF., 理学部, 助教授 (40004452)
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| Co-Investigator(Kenkyū-buntansha) |
KIRA Mitsuo TOHOKU UNIV., DEPT.CHEM., ASSOC.PROF. (40004452)
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| Project Period (FY) |
1993 – 1994
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| Project Status |
Completed (Fiscal Year 1994)
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| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1994: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1993: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Keywords | Hypercoordinate silicon / Fluoride Ion / Atom Transfer / Reaction Mechanism / Dynamic NMR / X-ray Crystallography / 5配位シリカート / トロポロナート / 動的NMR解析 |
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| Research Abstract |
Fluoride-ion exchange reactions between a tetracoordinate silane and the corresponding pentaccordinate fluorosilicate constitute a class of atom-transfer selfexchange reactions at a main-group atom center, the mechanism has been studied very scarcely. The exchange has been supposed to proceed via a transition state having linear arrangement of [Si-F-Si]. A theoretical study have shown that SiH_nF_<4-n> (n=1-3) forms a stable linear Si-F-Si bridge with [SiH_nF_<5-n>]^- in the gas phase. We have developed the synthesis and structure of novel intramolecular fluoride-ion donor-acceptor systems and related bissilicates. A dynamic ^<13>C NMR study has shown exchange of the fluoride-ions in the fluoride-ion donor-acceptor systems in both unimolecular and bimolecular processes. The large negative activation entropies for the bimolecular exchange suggest that the reaction proceeds via a rather unusual fluorine-bridged cyclophane-like transition states.
Crystal structures of the intramolecular fluoride-ion donor-acceptor systems have been analyzed by X-ray crystallography. These systems are expected to give a novel concept to design the ion conducting materials.
Novel neutral hexacoordinate silicates having tropolonate ligands were synthesized. X-ray crystallographic analysis for diphenyl- and dimethylbis (tropolonato)- silicates showed that these silicates have octahedral structure with the two alkyl and phenyl groups at the cis positions. Essentially no bond alternation in the C-C bonds of tropolonate rings suggests that the tropolonates serve as intramolecular countercations in the silicates. Analysis of the dynamic ^<13>C NMR spectra of these silicates revealed that there exists an isomerization process through a bond-rupture-recombination mechanism rather than a concerted mechanism.
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