OXIDATION OF POLYCYCLIC AROMATIC-HYDROCARBONS CATALYZED BY IRON TETRASULFOPHTHALOCYANINE FEPCS - INVERSE ISOTOPE EFFECTS AND OXYGEN LABELING STUDIES

Iron(III) tetrasulfophthalocyanine (FePcS) was shown to catalyze the o xidation of polycyclic aromatic hydrocarbons by H2O2. Benzo[a]pyrene a nd anthracene were converted, to the corresponding quinones while biph enyl-2,2'-dicarboxylic acid was the main product of phenanthrene oxida tion. The mechanism of the anthracene oxidation by H2O2 in the presenc e of FePcS or by KHSO5 with iron(III) meso-tetrakis(3,5-disulfonatomes ityl)porphyrin (FeTMPS) (see Figure 1 for catalyst structures) has bee n investigated in details by using kinetic isotope effects (KIEs) and O-18 labeling studies. KIEs measured on the substrate consumption in t he competitive oxidation of [H-10]anthracene and [D-10]anthracene by F ePcS/H2O2 and FeTMPS/KHCO5 were essentially the same, 0.75 +/- 0.02 an d 0.76 +/- 0.06, respectively. These inverse KIEs on the first oxidati on step can be explained by the sp(2)-to-sp(3) hybridization change du ring the addition of an electrophilic oxoiron complex to the sp(2) car bon center of anthracene to form a sigma adduct (this inverse KIE bein g enhanced by stronger stacking interactions between the perdeuterated substrate with the macrocyclic catalyst). Although the first oxidatio n step seems to be the same, different distribution of the oxidation p roducts of anthracene and very different O-18 incorporation into anthr one and anthraquinone in catalytic oxidations performed in the presenc e of (H2O)-O-18 suggested that different active species should be resp onsible for anthracene oxidation in both catalytic systems. All the re sults obtained are compatible with an involvement of TMPSFeV=O (or (TM PS+FeIV)=O), having two redox equivalents above the iron(III) state of the metalloporphyrin precursor, while PcSFeIV=O (one redox equivalent above Fe-III state of FePcS) was proposed to be the active species in the metallophthalocyanine-based system.