PHOTOCATALYTIC OXYGENATION OF HYDROCARBONS WITH (TETRAARYLPORPHYRINATO)IRON(III) COMPLEXES AND MOLECULAR-OXYGEN - COMPARISON WITH MICROSOMAL CYTOCHROME-P-450 MEDIATED OXYGENATION REACTIONS
L. Weber et al., PHOTOCATALYTIC OXYGENATION OF HYDROCARBONS WITH (TETRAARYLPORPHYRINATO)IRON(III) COMPLEXES AND MOLECULAR-OXYGEN - COMPARISON WITH MICROSOMAL CYTOCHROME-P-450 MEDIATED OXYGENATION REACTIONS, Journal of the American Chemical Society, 116(6), 1994, pp. 2400-2408
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.