Mechanisms for the formation of six-coordinate Fe(III)TPP-peroxide complexes studied by simultaneous ESR and optical measurements

Abstract

ESR and optical absorption measurements were performed for six-coordinate Fe(III)TPP-butyl peroxide complexes formed in the reaction system composed of Fe(III)TPPCl, NaOCH 3 and t- or n-butyl hydroperoxide. The presence of four paramagnetic iron complexes was detected in the reaction system. Based on the spectroscopic parameters, the spin state and the axial ligand of these species were deduced as follows: Fe(III)TPP-(HOCH 3)( −OCH 3) ( A), -( −OCH 3) 2 ( B), ( −OCH 3)( −OO-butyl) ( C), -( −OO-butyl) 2 ( D) coordination reactions of t- and n-butyl hydroperoxide and complexes A and B were monitored on changing the molar ratio of [t- or n-butylperoxide]/ [Fe(III)TPPCl]. The observed spectral changes justified that complexes A and B were successively changed to complex D through complex C. The concentration of these four paramagnetic complexes was estimated by means of the duplicate integration of the observed ESR spectra at 4.2 K. The molar distribution of complexes A, B, C and D was simulated by taking into account the formation constants relating to the generation of the peroxide complexes C and D. By comparison of the formation constants, the possible mechanisms for Fe(III)TPP-peroxide complex formation were discussed.