PHOTOCATALYTIC OXYGENATION OF HYDROCARBONS WITH (TETRAARYLPORPHYRINATO)IRON(III) COMPLEXES AND MOLECULAR-OXYGEN - COMPARISON WITH MICROSOMAL CYTOCHROME-P-450 MEDIATED OXYGENATION REACTIONS

Photocatalytic oxygenation of various alkenes with dioxygen and (5,10,15,20-tetraarylporphyrinato)iron(III) complexes yielded allylic oxygenation products and/or epoxides. The product composition was found to be influenced both by the nature of the used substrate and by the concentrations, as well as the axial ligands. Alkenes with strained carbon double bonds gave preferentially epoxides whereas mainly allylic oxygenation was observed for unstrained alkenes. The proposed reaction mechanisms involve the oxoiron(IV) porphyrinate (P)Fe(IV)=O as the catalytically active species whose selectivity is related to that of the oxygenation of alpha-pinene with microsomal cytochromes P-450 and P-420 obtained from the yeast strain Torulopsis apicola. Oxygenation products observed with both systems give evidence for the occurrence of an oxoiron(IV) heme species in microsomal cytochrome P-450 mediated reactions. The enantio-, regio-, and chemoselectivities of the photooxygenation with iron(III) porphyrins and molecular oxygen are explained in terms of abstraction of an allylic hydrogen atom, catalyzed autoxidation and ''direct'' oxygen-transfer reactions.