Synthesis of mononuclear non-heme iron(III)-hydroperoxo complex as an oxidative catalyst

Mononuclear Fe-II complex [Fe-II(ppba)](2+) (ppba = (6-pivalamido-2-pyridylmethyl) (2-pyridylmethyl)tert-butylamine) (1) has been synthesized and structurally characterized. The addition of H2O2 (10eq) to an acetone solution of 1 at -78 degrees C generated Fe(III)PPBA-OOH species, accompanied by a color change from pale yellow to reddish purple, which showed an intense absorption band corresponding to LMCT band (HOO- to Fe) at 528 nm (c = 1120 M-1 cm(-1)). The ESR spectrum for Fe(III)PPBA-OOH species (g(//) = 4.22, g(perpendicular to) = 7.70 in acetone at 77 K) was typical of a high-spin Fe-III species, suggesting that the Fe(III)PPBA-OOH species is maintained as a mononuclear complex in the solution state. The resonance Raman spectra, when (H2O2)-O-16 and (H2O2)-O-18 were used, exhibited intense bands characteristic to the O-O stretching vibrations at 880 cm(-1) nu(O-16-O-16) and 824 cm(-1) nu(O-18-O-18), respectively. These findings suggest that Fe(III)PPBA-OOH species is [Fe-III(ppba)(OOH)](2+) (2). In order to understand the catalytic reactivity of complex 2, oxidative reactions for some organic substrates by complex 2 were carried out in the presence of H2O2; thioanisole was oxidized to the corresponding sulfoxide and sulfone, respectively, and furthermore, cyclohexene was converted to cyclohexene oxide, cyclohexenol and cyclohexenone.