The hydroxylation of unactivated alkanes has been observed in a catalytic system containing iodosylbenzene and various iron porphyrins. The yields and distributions of products have been found to be sensitive to the peripheral substitution pattern of the porphyrin. The oxidation of cyclohexane with chloro(5,10,15,20-tetra-otolylporphyrinato)iron(III) [Fe(TTP)Cl] gave a 31% yield of cyclohexanol and 6% cyclohexanone based on iodosylbenzene. Two samples of Fe(TTP)ClCl with differing atropisomeric composition gave different product ratios. The hydroxylation of cycloheptane under these conditions and in the presence of bromotrichloromethane gave 24% cycloheptanol and 18% bromocycloheptane. Steric selectivity was observed by comparing the hydroxylation of cis-decalin with Fe(TPP)Cl, Fe(TTP)Cl, Fe(TNP)Cl, and Fe(TMP)Cl. The hydrogen-isotope effect for cyclohexane hydroxylation by Fe(TTP)Cl was found to be 12.9 ± 1. A mechanism for hydroxylation is proposed on the basis of these results that involves initial oxidation of the iron porphyrin, hydrogen atom abstraction from the alkane, and rapid collapse of this radical to give the product alcohol and to regenerate the iron(III) catalyst.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry