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 oxygen ation products and/or epoxides. The product composition was found to b e influenced both by the nature of the used substrate and by the conce ntrations, as well as the axial ligands. Alkenes with strained carbon double bonds gave preferentially epoxides whereas mainly allylic oxyge nation was observed for unstrained alkenes. The proposed reaction mech anisms involve the oxoiron(IV) porphyrinate (P)Fe(IV)=O as the catalyt ically active species whose selectivity is related to that of the oxyg enation of alpha-pinene with microsomal cytochromes P-450 and P-420 ob tained from the yeast strain Torulopsis apicola. Oxygenation products observed with both systems give evidence for the occurrence of an oxoi ron(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 an d ''direct'' oxygen-transfer reactions.