Ferroxime(II)-catalysed oxidation of 3,5-di-tert-butylcatechol by O2. Kinetics and mechanism †

Abstract

The complex [Fe(Hdmg) 2 (MeIm) 2 ] 1, referred to as ferroxime(), was found to be the precursor of a selective catalyst for the oxidative dehydrogenation of 3,5-di-tert-butylcatechol (H 2 dbcat) to the corresponding 1,2-benzoquinone (dtbq) at room temperature and atmospheric dioxygen pressure. The observed kinetic behaviour in MeOH is consistent with solvolysis of one MeIm ligand and binding of dioxygen to the five-co-ordinate intermediate to form a superoxo complex. The latter abstracts an H atom from H 2 dbcat via a hydrogen-bonded ternary active intermediate, affording the semiquinone anion radical dbsq Ϫ and [Fe III (Hdmg) 2 (MeIm)(O 2 H)]. Utilising an electron and a proton from H 2 dbcat, the latter undergoes heterolytic cleavage to yield a ferryl species, which rapidly oxidises a second H 2 dbcat. Complexation of dbsq Ϫ with [Fe II (Hdmg) 2 (MeIm)] affords a strongly coloured paramagnetic species [Fe II (Hdmg) 2 (MeIm)(dbsq Ϫ )], which persists throughout the catalytic reaction, acting as buffer for dbsq Ϫ . The proposed mechanism involves steps similar to those of the known cytochrome P450 cycle, with H 2 dbcat acting as both ancillary electron source and substrate.

An efficient method to investigate metal?ligand combinations for oxygen bleaching

“…The high activity of Cu-dmg has not been reported earlier. Simandi et al [37][38][39] have studied iron(II) and cobalt(II) oxime catalysed oxidative dehydrogenation of catechols with dioxygen, but no applications of copper are reported. Most publications concerning Cu-dmg complexes merely describe the structure of the complex and its redox properties [40][41][42][43][44][45].…”

Syntheses, structures and catecholase activity of two cobalt(III) complexes derived from N,N′-ethylenebis(3-ethoxysalicylaldiimine): A special host–guest system from a special ligand

“…In most of the catecholase activity studies, 3,5-di-tert-butylcatechol (3,5-DTBCH 2 ) has been employed as the model substrate because (i) It is easily oxidized to 3,5-DTBQ and (ii) the generated product, 3,5-di-tert-butylquinone (3,5-DTBQ), has a characteristic absorption band at around 400 nm [24,[40][41][42][43][44][45][46][47][48][49][50][51][52][53]. Therefore, activity and kinetic parameters can be determined by monitoring the absorption maximum of the quinone.…”

“…Although catechol oxidase, which catalyzes aerial oxidation of catechol to o-quinone, contains a dicopper(II) active site [40,41], a number of functional model compounds of other metal ions are known to show this activity [24,[42][43][44][45][46][47][48][49][50][51][52][53]. Those model compounds include manganese(II) [42], manganese(III) [24,43], manganese(IV) [44], manganese(III)manganese(II) [45], manganese(III) manganese(III) [46], iron(II) [47], iron(III) [48], cobalt(II) [49,50], cobalt(III)cobalt(II) [51][52][53] and cobalt(III)cobalt(III) systems [53].…”

“…Those model compounds include manganese(II) [42], manganese(III) [24,43], manganese(IV) [44], manganese(III)manganese(II) [45], manganese(III) manganese(III) [46], iron(II) [47], iron(III) [48], cobalt(II) [49,50], cobalt(III)cobalt(II) [51][52][53] and cobalt(III)cobalt(III) systems [53]. Recently, we have reported a series of mononuclear manganese(III) compounds derived from H 2 L OEt-en (N,N 0 -ethylenebis(3-ethoxysalicylaldiimine); Scheme 1) as functional models of catechol oxidase activity [24].…”

“…Spectral profile showing the increase of quinone band at 400 nm after the addition of 100 fold of 3,5-DTBCH 2 to a solution containing complex 2 (0.25 Â 10 À4 M) in DMF. Spectra were recorded after each 5 min [24,[40][41][42][43][44][45][46][47][48][49][50][51][52][53]…”