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Remarkable Solvent, Porphyrin Ligand, and Substrate Effects on Participation of Multiple Active Oxidants in Manganese(III) Porphyrin Catalyzed Oxidation Reactions

Authors

  • Min Young Hyun,

    1. Department of Fine Chemistry, Seoul National University of Science & Technology, Seoul 139-743 (Korea), Fax: (+82) 2-973-9149
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  • Young Dan Jo,

    1. Department of Fine Chemistry, Seoul National University of Science & Technology, Seoul 139-743 (Korea), Fax: (+82) 2-973-9149
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  • Jun Ho Lee,

    1. Department of Chemistry, Research Institute for Natural Sciences, Korea University, 5 Anam-dong, Sungbuk-gu, Seoul 136-701 (Korea)
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  • Hong Gyu Lee,

    1. Department of Fine Chemistry, Seoul National University of Science & Technology, Seoul 139-743 (Korea), Fax: (+82) 2-973-9149
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  • Hyun Min Park,

    1. Department of Fine Chemistry, Seoul National University of Science & Technology, Seoul 139-743 (Korea), Fax: (+82) 2-973-9149
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  • In Hong Hwang,

    1. Department of Fine Chemistry, Seoul National University of Science & Technology, Seoul 139-743 (Korea), Fax: (+82) 2-973-9149
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  • Kyeong Beom Kim,

    1. Department of Fine Chemistry, Seoul National University of Science & Technology, Seoul 139-743 (Korea), Fax: (+82) 2-973-9149
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  • Prof. Suk Joong Lee,

    Corresponding author
    1. Department of Chemistry, Research Institute for Natural Sciences, Korea University, 5 Anam-dong, Sungbuk-gu, Seoul 136-701 (Korea)
    • Department of Chemistry, Research Institute for Natural Sciences, Korea University, 5 Anam-dong, Sungbuk-gu, Seoul 136-701 (Korea)
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  • Prof. Cheal Kim

    Corresponding author
    1. Department of Fine Chemistry, Seoul National University of Science & Technology, Seoul 139-743 (Korea), Fax: (+82) 2-973-9149
    • Department of Fine Chemistry, Seoul National University of Science & Technology, Seoul 139-743 (Korea), Fax: (+82) 2-973-9149
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Abstract

The participation of multiple active oxidants generated from the reactions of two manganese(III) porphyrin complexes containing electron-withdrawing and -donating substituents with peroxyphenylacetic acid (PPAA) as a mechanistic probe was studied by carrying out catalytic oxidations of cyclohexene, 1-octene, and ethylbenzene in various solvent systems, namely, toluene, CH2Cl2, CH3CN, and H2O/CH3CN (1:4). With an increase in the concentration of the easy-to-oxidize substrate cyclohexene in the presence of [(TMP)MnCl] (1 a) with electron-donating substituents, the ratio of heterolysis to homolysis increased gradually in all solvent systems, suggesting that [(TMP)Mn[BOND]OOC(O)R] species 2 a is the major active species. When the substrate was changed from the easy-to-oxidize one (cyclohexene) to difficult-to-oxidize ones (1-octene and ethylbenzene), the ratio of heterolysis to homolysis increased a little or did not change. [(F20TPP)Mn[BOND]OOC(O)R] species 2 b generated from the reaction of [(F20TPP)MnCl] (1 b) with electron-withdrawing substituents and PPAA also gradually becomes involved in olefin epoxidation (although to a much lesser degree than with [(TMP)Mn[BOND]OOR] 2 a) depending on the concentration of the easy-to-oxidize substrate cyclohexene in all aprotic solvent systems except for CH3CN, whereas MnV[DOUBLE BOND]O species is the major active oxidant in the protic solvent system. With difficult-to-oxidize substrates, the ratio of heterolysis to homolysis did not vary except for 1-octene in toluene, indicating that a MnV[DOUBLE BOND]O intermediate generated from the heterolytic cleavage of 2 b becomes a major reactive species. We also studied the competitive epoxidations of cis-2-octene and trans-2-octene with two manganese(III) porphyrin complexes by meta-chloroperbenzoic acid (MCPBA) in various solvents under catalytic reaction conditions. The ratios of cis- to trans-2-octene oxide formed in the reactions of MCPBA varied depending on the substrate concentration, further supporting the contention that the reactions of manganese porphyrin complexes with peracids generate multiple reactive oxidizing intermediates.

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