An Iron(II)[1,3‐bis(2′‐pyridylimino)isoindoline] Complex as a Catalyst for Substrate Oxidation with H₂O₂ – Evidence for a Transient Peroxidodiiron(III) Species

Abstract

The complex [Fe(indH)(solvent)3](ClO4)2 (1) has been isolated from the reaction of equimolar amounts of 1,3-bis(2′-pyridylimino)isoindoline (indH) and Fe(ClO4)2 in acetonitrile and characterized by X-ray crystallography and several spectroscopic techniques. It is a suitable catalyst for the oxidation of thioanisoles and benzyl alcohols with H2O2 as the oxidant. Hammett correlations and kinetic isotope effect experiments support the involvement of an electrophilic metal-based oxidant. A metastable green species (2) is observed when 1 is reacted with H2O2 at −40 °C, which has been characterized to have a FeIII(μ-O)(μ-O2)FeIII core on the basis of UV-Vis, electron paramagnetic resonance, resonance Raman, and X-ray absorption spectroscopic data.

Catalytic oxidation of alcohols and sulfides with hydrogen peroxide using isoindoline and phthalazine-based diiron complexes

“…See Table 5 with each para-substituted benzyl alcohol derivatives (Table 6)) gave a value of −0.8 (Fig. 10), which is comparable to that of the closely related 1/H 2 O 2 system [33], and ten times larger than those obtained with bona fide non-heme oxidoiron(IV) complexes ( = −0.07) [47]. For the determination of the kinetic isotope effect (KIE), separate reactions were carried out for benzyl alcohol and D 7 -benzyl alcohol with the complex 8 and H 2 O 2 ( Table 6).…”

“…8), that is consistent with a concerted mechanism in which an electrophilic active oxygen species is attacked by a nucleophilic sulfide, with the electron-rich substrates displaying the highest reactivity. This value is two times larger than that of the 1/H 2 O 2 ( = −0.40) system [33], and 1.5 times smaller than that was obtained for oxygen-atom transfer reaction catalyzed by [Fe III (salen)] + /H 2 O 2 ( = −1.50) [7]. It is interesting to compare the results of log k rel vs E ox plots obtained here for complex 8 with the recent observations made by Goto et al [46] on the sulfoxidation catalyzed by high-valent intermediates of heme enzymes.…”

“…We have previously reported the synthesis and crystal structures of a -oxido-bridged diiron(III) complex, [Fe 2 (-O)(L 1 ) 2 Cl 2 ] (2) and a new iron(II) complex, [Fe(HL 1 )(CH 3 CN) 3 ](ClO 4 ) 2 (1), and their catalytic activity on the oxidation of thioanisoles and benzyl alcohols [31][32][33]. We have also reported the spectroscopic characterization of a transient green species, Fe III (-O)(-1,2-O 2 )Fe III derived from the reaction of 1 with H 2 O 2 upon the formation of 2, which is linked somehow to the observed oxidative reactivity (Scheme 2).…”

Transition Metal Complexes and the Activation of Dioxygen

“…For example, a transient species formulated as a (μ-oxo)(μ-1,2-peroxo)diiron(III,III) complex was identified via spectroscopy in studies of oxidations using H 2 O 2 with a tridentate, meridional N-donor ligand [238]. However, the authors surmised that an unidentified species derived from the observed intermediate was likely the actual oxidant in the catalytic reactions.…”

1,3-Bis(5′-methyl-4′-phenyl-2′-thiazolylimino)isoindoline

“…This can create an advantageous situation for cyclometallation [3] or intramolecular oxidative CH bond (benzylic and/or aromatic) activation reactions via peroxo or high valent oxo species [4].…”