Epoxidation and Hydroxylation Catalyzed By Ferric Porphyrins.

The combination of iodosylbenzene and ferric porphyrins was investigated and has been shown to be a novel oxidizing system that partially models the reactivity of cytochome P-450. Alkanes were hydroxylated and alkenes were epoxidized by oxygen atom transfer from iodosylbenzene catalyzed by ferric porphyrins. Cyclohexene oxide was produced in 55% yield and cyclohexene-3-ol in 15% yield, in the oxidation of cyclohexene catalyzed by meso-tetraphenylporphinato iron(III) chloride (Fe('+3) ClTPP). The epoxidation reaction was stereospecific and proceeded faster with electron-rich olefins. When Fe('+3) ClTPP with substituents on the ortho positions of the phenyl rings was used, cis double bonds were epoxidized more readily than trans double bonds. The epoxidation of trans, trans, cis-(1,5,9)-cyclododecatriene with iodosylbenzene catalyzed by meso-tetra(mesityl)porphinato iron (III) chloride (Fe('+3)ClTMP) produced mainly (86%) the cis epoxide. The selectivity for the epoxidation of cis double bonds in preference to trans double bonds was rationalized by a mechanism incorporating an iron-bound oxygen atom as the active oxidant. The hydroxylation of aliphatic substrates proceeded with retention of stereochemistry, and with a selectivity for tertiary over secondary carbon-hydrogen bonds. For example, 1-adamantanol was formed 48 times faster than 2-adamantanol in the Fe('+3) ClTPP catalyzed reaction. Cyclohexane-d(,112) was 12.9 (+OR-) 1 times more reactive than cyclohexane, indicating the hydroxylation reaction proceeded with a large deuterium kinetic isotope effect. Oxidation norcarane did not result in an opening of the cyclopropane ring. Oxidation of norbornene produced a 36:1 mixture of exo- and endo-norborneols, respectively. Carbon tetrachloride did not affect the hydroxylation of norbornane, indicating free-radicals were not captured. The free-radical traps, oxygen and bromotrichloromethane did, however, affect the oxidation of cyclohexene and cycloheptane, respectively. The distribution of products obtained from the hydroxylation of cis-decahydronaphthalene and adamantane was dependent on the structure of the ferric porphyrin catalyst employed. The hydroxylation reaction was discussed in terms of a hydrogen atom abstraction by an iron-oxo species, followed by a rapid lig and transfer oxidation of the alkane radical. meso-Tetra-(ortho-tolyl)porphinato iron(III) chloride (Fe('+3)ClTTP) was a superior hydroxylation catalyst compared to Fe('+3)ClTPP and cyclohexane was oxidized to cyclohexanol and cyclohexanone in 22% and 2% yield. When Fe('+3) ClTPP was used, cyclohexanol was produced in 8% yield. It was possible to partially separate the atropisomers of Fe('+3)ClTTP by column chromatography. The (alpha),(alpha),(beta),(beta) and (alpha),(beta),(alpha),(beta) atropisomers of Fe('+3)ClTTP were determined to be the most efficient hydroxylation catalysts and were responsible for the increased efficiency of Fe('+3)ClTPP compared to Fe('+3)-ClTPP. The reaction of Fe('+3)ClTMP with iodosylbenzene at low temperatures (-40(DEGREES)C) generated a stable intermediate that was reactive with cycloolefins but unreactive with trans-hex-3-ene. The low temperature intermediate did not have an ESR absorption, indicating that it was not a simple iron-(III) porphyrin. The reaction of a Fe('+3)ClTMP with aqueous sodium hydroxide produced a new porphyrin which was characterized as Fe('+3)(OH)TMP.PhDOrganic chemistryUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/158561/1/8204574.pd