1993 Fiscal Year Final Research Report Summary
Construction of Artificial Photosynthetic System : Photochemical Epoxidation with Visible Light using Water as both an Electron and Oxygen Donor
| Project/Area Number |
04453090
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
有機工業化学
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| Research Institution | Tokyo Metropolitan University |
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Principal Investigator |
INOUE Haruo Tokyo Metropolitan Univ.Fac.of Tech., Dep.Ind.Chem.Professor, 工学部, 教授 (90087304)
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| Co-Investigator(Kenkyū-buntansha) |
SHIRAGAMI Tsutomu Tokyo Metropolitan Univ.Fac.of Tech., Dep.Ind.Chem.Research Associate, 工学部, 助手 (60235744)
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| Project Period (FY) |
1992 – 1993
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| Keywords | Artificial Photosynthesis / Metalloporphyrin / Epoxy Compound / Electron Transport / Hydrogen Evolution / Methylviologen / Cyclohexene / Potassium Hexachloroplatinate |
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| Research Abstract |
As a model reaction system of artificial photosynthesis, photochemical oxygenation of alkene in the photoredox system involving water as an electron donor, high valent metalloporphyrins as sensitizers, and methylviologen or potassium hexachloroplatinate as an electron acceptor has been investigated. Sb(V), P(V), Sn(IV), and Ge(IV) tetraphenylporphyrin(TPP) were used as high valent metalloporphyrins. The oxygenation products of cyclohexene were cyclohexeneoxide, 2-cyclohexenol, cyclohexene-1,2-diol, 2-cyclohexenone, and 2-chlorocyclohexanol. Hexachloroplatinate as an electron acceptor afforded larger quantum yield of the photooxygenation by a factor of 50 than methylviologen. Oxygen atom of water was confirmed to be incorporated in the oxygenation product by experiments using H_2^<18>O.Hydrogen evolution catalyzed by colloidal platinum was also observed when methylviologen was used as an electron acceptor. Water molecule was thus confirmed to act as both oxygen and electron donor in the photoredox system under visible light irradiation. Laser flash photolysis studies on Sb(V)TPP sensitized photooxygenation revealed that the lowest excited triplet state of Sb(V)TPP was responsible for the reaction. Deprotonation of the axially ligated hydroxyl group in the excited triplet state of Sb(V)TPP and subsequent electron transfer to methylviologen led to formation of a key intermediate metal-oxo complex. Formation of cation radical of Sb(V)TPP by an electron transfer to hexachloroplatinate from the triplet Sb(V)TPP and subsequent deprotonation of the cation radical also produced the metal-oxo complex. Oxygen atom of water was activated as that of the metal-oxo complex and was transferred to alkene.
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