IRON(III) PORPHYRINS ATROPISOMERS AS CATALYSTS FOR CYCLOHEXANE HYDROXYLATIONS - A BIOMIMETICAL SYSTEM

Cyclohexane hydroxylation, using iodosylbenzene as oxygen donor was catalyzed by iron(III) 5,10,15,20-tetrakis(tetradecyl-2-pyridyl)porphyrin chloride ((FeTTD2PyP)Cl-5). The long chain ortho-substituents prevent the free rotation of the pyridynium rings originating in the atropisomers: alpha alpha alpha alpha, alpha alpha alpha beta, alpha alpha beta beta, alpha beta alpha beta. The apolar alkyl groups and peripheric positive charges give to these porphyrins an amphyphylic character, viabilizing reactions in acetonitrile and dichloromethane. The hydroxylations yields were affected by the steric environment around the metallic ion. The most polar 6b (alpha alpha alpha alpha, alpha alpha alpha beta) and less polar 6a (alpha alpha beta beta, alpha beta alpha beta) atropisomers fractions promote distinct environments depending on the solvent polarity. The most polar atropisomers fraction 6b has been shown to be a better catalyst than the less polar fraction and the other unprotected iron porphyrins. The hydrophobic alkyl long chains in 6b confer some organization to the system, and the reaction site environment works with low concentration (6 x 10(-5) mol.L(-1)) and high efficiency, representing a good biomimetic system.