https://scholarworks.unist.ac.kr/handle/201301/135 2026-04-20T02:43:44Z 2026-04-20T02:43:44Z Lim, Mi Hee Lee, YJ Goh, YM Nam, W Kim, C https://scholarworks.unist.ac.kr/handle/201301/8673 2023-12-22T03:11:55Z 1999-03-31T15:00:00Z

Title: Hydroxylation of aliphatic hydrocarbons with m-chloroperbenzoic acid catalyzed by electron-deficient iron(III) porphyrin complexes Author(s): Lim, Mi Hee; Lee, YJ; Goh, YM; Nam, W; Kim, C Abstract: The catalytic hydroxylation of aliphatic hydrocarbons by m- chloroperbenzoic acid (MCPBA) has been studied in the presence of electron- deficient iron(III) porphyrin complexes. High yields of alcohol products were obtained with small amounts of ketone formation under mild reaction conditions. The stereospecificity and regioselectivity of the iron porphyrin complexes have been investigated in hydroxylation reactions as well. The hydroxylation of alkanes has been performed in the presence of isotopically 18O-labeled water, H2 18O, in order to understand the effects of the electronic nature of iron porphyrin complexes, the concentration of H2 18O, the C-H bond strength of alkanes, and the reaction temperature on the 18O- incorporation from the labeled water into alcohols. We found that the amounts of 18O incorporated into the alcohol products varied in the reactions; these results were interpreted with that the reaction of oxygen atom transfer from a high-valent iron oxoporphyrin complex to alkanes competes with that of oxygen atom exchange between the intermediate and labeled water that leads to 18O-incorporation from H2 18O into the alcohol products. Deuterium kinetic isotope effects (KIEs) in the alkane hydroxylations by the iron porphyrin complexes and MCPBA have been studied with a mixture of cyclohexane and cyclohexane-d12. The KIE values obtained in the reactions were found to depend significantly on the nature to the iron porphyrin complexes. The temperature dependence of k(H)/k(D) was also studied from -40 to 25 °C and the parameters of Arrhenius equation (i.e., the pre-exponential factor ratio, A(H)/A(D), and the isotopic difference of C-H and C-D bond activation energies, E(a)(D)-E(a)(H)) were determined.

1999-03-31T15:00:00Z Nam, W Goh, YM Lee, YJ Lim, Mi Hee Kim, C https://scholarworks.unist.ac.kr/handle/201301/8672 2023-12-22T03:11:14Z 1999-05-31T15:00:00Z

Title: Biomimetic alkane hydroxylations by an iron(III) porphyrin complex with H2O2 and by a high-valent iron(IV) oxo porphyrin cation radical complex Author(s): Nam, W; Goh, YM; Lee, YJ; Lim, Mi Hee; Kim, C Abstract: n iron(III) porphyrin complex with highly electron-withdrawing substituents on the porphyrin ligand efficiently catalyzes the hydroxylation of alkanes by H2O2 via enzyme mimetic oxidation reactions in aprotic solvent. An "isolated" high-valent iron(IV) oxo porphyrin cation radical intermediate, prepared in situ by reaction of the iron porphyrin complex with m-CPBA at -40 degrees C, is capable of activating C-H bonds of alkanes to give oxygenated products efficiently. The hydroxylating intermediate generated in the catalytic H2O2 reaction is evidenced to be the high-valent iron(IV) oxo porphyrin cation radical species.

1999-05-31T15:00:00Z Nam, W Oh, SY Lim, Mi Hee Choi, MH Han, SY Jhon, GJ https://scholarworks.unist.ac.kr/handle/201301/8671 2023-12-22T03:09:02Z 1999-12-31T15:00:00Z

Title: Temperature effect on the epoxidation of olefins by an iron(III) porphyrin complex and tert-alkyl hydroperoxides Author(s): Nam, W; Oh, SY; Lim, Mi Hee; Choi, MH; Han, SY; Jhon, GJ Abstract: An electron-deficient iron porphyrin complex catalyzes the epoxidation of olefins by tert-alkyl hydroperoxides via radical-free oxidation reactions in aprotic solvent; the epoxidation reactions were markedly influenced by reaction temperature and high yields of epoxide products were obtained with retention of stereospecificity at low temperature.

1999-12-31T15:00:00Z Nam, WO Lim, Mi Hee Lee, HJ Kim, C https://scholarworks.unist.ac.kr/handle/201301/8669 2023-12-22T03:07:25Z 2000-06-30T15:00:00Z

Title: Evidence for the participation of two distinct reactive intermediates in iron(III) porphyrin complex-catalyzed epoxidation reactions Author(s): Nam, WO; Lim, Mi Hee; Lee, HJ; Kim, C Abstract: We have studied the competitive epoxidations of olefins with cis- and trans-stilbenes and with cyclooctene and trans-stilbene in iron porphyrin complex-catalyzed epoxidation reactions by H2O2, tert-butyl hydroperoxide (t-BuOOH), and m-chloroperoxybenzoic acid (m-CPBA) in protic solvent (i.e., a solvent mixture of CH3OH and CH2Cl2) and aprotic solvent (i.e., a solvent mixture of CH3CN and CH2Cl2) at room temperature under catalytic reaction conditions. The competitive epoxidations were also carried out with in situ generated high-valent iron(IV) oxo porphyrin cation radical complexes in aprotic solvent under stoichiometric reaction conditions. By determining the ratios of epoxide products formed in the competitive epoxidations, we were able to conclude unambiguously that the reactive species generated in protic solvent are high-valent iron(IV) oxo porphyrin cation radical complexes 3 and the intermediates formed in aprotic solvent are oxidant-iron porphyrin intermediates 2. A protic solvent such as methanol is proposed to function as a general-acid catalyst, thereby increasing the rate of O-O bond cleavage of 2 to form 3. In the absence of general-acid catalysis such as in aprotic solvent, the rate of O-O bond cleavage of 2 is relatively slow and 2 transfers its oxygen to olefins prior to the formation of 3. To further examine the effect of the general-acid catalysis on the nature of epoxidizing intermediates, we carried out competitive epoxidations in the solvent mixtures of alcohol/CH2Cl2 using alcohols of varying pK(a) values and in the presence of an acid (i.e., HClO4) in aprotic solvent. The product ratios were found to vary depending on the strength of the solvent acidity, demonstrating that the reaction of 2 with olefin competes with the O-O bond cleavage of 2 that leads to the formation of 3. We also reported for the first time that a high-valent iron(IV) oxo porphyrin cation radical intermediate containing electron-deficient porphyrin ligand shows an unexpected preference for trans-stilbene over cis-stilbene in the competitive epoxidations of cis- and trans-stilbenes.

2000-06-30T15:00:00Z