Methylene bridge regulated geometrical preferences of ligands in cobalt(iii) coordination chemistry and phenoxazinone synthase mimicking activity

Abstract

Two new azide bound cobalt(III) complexes, [Co(L(1))(N3)3] (fac-1) and [Co(L(2))(N3)3] (mer-2), where L(1) is bis(2-pyridylmethyl)amine and L(2) is (2-pyridylmethyl)(2-pyridylethyl)amine, derived from tridentate reduced Schiff-base ligands have been reported. Interestingly, a methylene bridge regulated preferential coordination mode of ligands is noticed in their crystal structures: it is found in a facial arrangement in fac-1 and has a meridional disposition in mer-2. Both complexes show phenoxazinone synthase-like activity and the role of the structural factor on the catalytic activity is also explored. Moreover, the easily reducible cobalt(III) center in mer-2 favors the oxidation of o-aminophenol. The ESI-MS positive spectra together with UV-vis spectroscopy clearly suggest the formation of a catalyst-substrate adduct by substitution of the coordinated azide ions in the catalytic cycle.

Investigation of 3d-transition metal acetates in the oxidation of substituted dioxolene and phenols

“…The native enzyme is known to require 4-5 copper centres for maximum activity and less number of copper centres reduces the activity [156]. However, the model complexes of PHS are mostly rather simple mononuclear complexes of transition metal [71,[85][86][87][88][89][90][91][92][93][94][95]167]. There is only one report of a tetranuclear Cu II complex as model of phenoxazinone synthase by Mukherjee et al In that report the ligand is also attributed to be important for the activity due to its redox non-innocent nature [94].…”

“…PHS mimics cannot be found as much as CO but yet are well studied with 3d-metals viz. Co [85][86][87][88][89][90][91][92], Mn [71,89,91,93], Cu [94], Fe [91,95] complexes using 2-aminophenol as substrate. We investigated the possible reactive oxygen species (ROS) involved for each of the metal ions.…”

Syntheses, Structures and Phenoxazinone Synthase Activities of Two Cobalt(III) Complexes

“…The oxidation of 2‐aminophenol with molecular oxygen in the presence of bis‐benzimidazole diamide Fe(III) complexes, oximatoiron(II) complexes have been reported . Recently, oxidation of 2‐aminophenol by mononuclear cobalt(II) or cobalt(III) complexes have been explored . Several cobalt(II) complexes, such as cobalt(II)phthalo‐cyaninetetrasodium‐sulfonate, oximatocobalt(II) complexes, cobaloxime derivatives have been employed .…”

Influence of anionic co-ligands on the structural diversity and catecholase activity of copper(ii) complexes with 2-methoxy-6-(8-iminoquinolinylmethyl)phenol

“…We have recently reported several transition metal complexes those were found to be efficient functional models for phenoxazinone synthase [37][38][39][40] and catechol oxidase. 41 Close inspection of our previous results suggests that both the substitutionally labile coordination sites and the electronic environment of the metal center play important role for the biomimetic catalytic activity.…”

“…41 Close inspection of our previous results suggests that both the substitutionally labile coordination sites and the electronic environment of the metal center play important role for the biomimetic catalytic activity. [37][38][39][40][41] From the reports in the literature on various copper(II) model compounds [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] and from the crystal structure of catechol oxidase, 9 it is also clear that the active site of functional models must have free coordination sites available for substrate binding. Therefore, the ligands having lesser number of donor atoms are more promising.…”