Dinuclear mixed-valence CoIIICoII complexes derived from a macrocyclic ligand: unique example of a CoIIICoII complex showing catecholase activity

Abstract

The work in this paper presents the syntheses, characterization, catecholase activity, and electrospray ionization mass spectroscopic (ESI-MS positive) study of three mixed-valence dinuclear Co(III)Co(II) complexes of composition [Co(III)Co(II)L(N(3))(3)]·CH(3)CN (1), [Co(III)Co(II)L(OCN)(3)]·CH(3)CN (2), and [Co(III)Co(II)L(μ-CH(3)COO)(2)](ClO(4)) (3), derived from a tetraimino diphenolate macrocyclic ligand H(2)L, obtained on [2 + 2] condensation of 4-ethyl-2,6-diformylphenol and 2,2'-dimethyl-1,3-diaminopropane. While 1 and 2 are diphenoxo-bridged, 3 is a heterobridged bis(μ-phenoxo)bis(μ-acetate) system. Utilizing 3,5-di-tert-butyl catechol (3,5-DTBCH(2)) as the substrate, the catecholase activity of all the three complexes has been checked in methanol/acetonitrile/N,N-dimethyl formamide. While 2 and 3 are inactive, complex 1 shows catecholase activity with turnover numbers of 482.16 h(-1) and 45.38 h(-1) in acetonitrile and methanol, respectively. Electrospray ionization mass (ESI-MS positive) spectra of complexes 1-3 have been recorded in acetonitrile solutions and the positive ions have been well characterized. The ESI-MS positive spectrum of complex 1 in the presence of 3,5-DTBCH(2) has also been recorded and, interestingly, two positive ions [Co(III)Co(II)L(N(3))(2)(3,5-DTBCH(-))H](+) and [Co(II)Co(II)L(μ-3,5-DTBCH(2-))Na](+) have been identified.

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

“…The values are 3.93 and 4.4 for 1 and 2, respectively. The values are much larger than 3 but such large BVS values of Co III centers are not unusual [51,53,60].…”

“…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].…”

Synthesis and bio-catalytic activity of isostructural cobalt(III)-phenanthroline complexes

“…To reveal high catalytic activity of [1] + , we drew a comparison between our cobalt(III) complex and some other mono-and polynuclear cobalt complexes. [32][33][34][35] The data obtained from the Lineweaver-Burk plot model were used for a comparison of catalytic activity towards the oxidation of 3,5-DTBC as shown in figure S5 (Scheme 3). Most importantly, characteristic peaks are observed at m/z = 243.55 and 641.02.…”