Dioxygen activation and catalytic oxidation of triphenylphosphine by iron phthalocyanine compounds

The oxidation of PPh3 by molecular oxygen in toluene has been investigated through the use of phthalocyaninatoiron(II), (PcFe), and its corresponding bis-adducts of formula PcFe(N-base)2 (N-base = pyridine, 4-methylpyridine, piperidine, N-methylimidazole and imidazole) as catalysts. No oxidation was observed at 1 atm pressure, whereas both homogeneous and heterogeneous catalytic oxidation of PPh3 occurred at po2 = 60 - 70 atm at room temperature. Heterogeneous catalysis was observed with PcFe and PcFe(imidazole)2 which are both insoluble in toluene. Homogeneous catalysis in toluene solution was observed in all the other cases studied. The Nbase appears to play an important role in maintaining the conditions required for the Fe(II) ? Fe(III) redox reaction. ?-Oxobis(phthalocyaninatoiron(III)), i.e. (PcFe)2O, appears to be the final oxygen-containing species formed by PcFe and its N-base adducts during the irreversible reaction involved. An 'oxenic' species of formula pyPcFeO is proposed as the intermediate active 'oxygen atom transfer agent' in the catalytic process, which seems to proceed via a non-radical pathway.