Journal of the American Chemical Society p. 8462 - 8470 (1988)
Update date:2022-08-22
Topics:
Battioni, P.
Renaud, J. P..
Bartoli, J. F.
Reina-Artiles, M.
Fort, M.
Mansuy, D.
Fe and Mn porphyrins alone are almost unable to catalyze cyclooctene epoxidation or cyclooctane hydroxylation by H2O2.In the presence of imidazole, Mn(III) porphyrins, and particularly Mn(TDCPP)Cl, are much better catalysts than Fe porphyrins for oxygen-atom transfer from H2O2 to hydrocarbons.From a study of various Mn porphyrin catalysts and nitrogen base cocatalysts, the most efficient system that has been selected involves Mn(TDCPP)Cl in the presence of 10 - 20 equiv of imidazole.This system leads to high yields of alkene epoxidation (90 - 100 percent in less than 1 h at room temperature).Epoxidation of 1,2-dialkylethylenes is stereospecific and corresponds to a syn addition of an oxygen atom to the double bond.This system also leads to the oxidation by H2O2 of various alkanes such as cyclohexane, cyclooctane, adamantane, ethylbenzene, or tetralin, with formation of the corresponding alcohols and ketones in yields between 40 and 80 percent.The Mn(TDCPP)Cl-imidazole-PhIO and Mn(TDCPP)Cl-imidazole-H2O2 systems exhibit the following: (i) identical stereospecificities for the epoxidation of stilbene and hex-2-ene, (ii) identical regioselectivities for the epoxidation of iosoprene and limonene as well as for the hydroxylation of n-heptane, and (iii) almost identical chemoselectivities for the oxidation of cyclohexene and of mixtures of cyclooctane and cyclooctene.This indicates that very similar, if not identical, high-valent Mn-oxo intermediates are the active oxygenating species in both systems.Thus, thanks to the presence of imidazole, it is possible to perform efficient biomimetic monooxygenations of hydrocarbons by using the Mn(TDCPP)Cl catalyst and H2O2 instead of PhIO as the oxygen-atom donor.
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