Exclusive selectivity of multidentate ligands independent on the oxidation state of cobalt: influence of steric hindrance on dioxygen binding and phenoxazinone synthase activity

Abstract

The present report describes the syntheses, characterizations, crystal structures and study of the phenoxazinone synthase activity of two peroxo-bridged dicobalt(III) complexes, [Co2(L(1))2(μ-O2)](ClO4)4·2CH3CN (1) and [Co2(L(2))2(μ-O2)](ClO4)4 (2), and three mononuclear cobalt(II) complexes, [Co(L(3))(CH3CN)](ClO4)2 (3), [Co(L(4))(H2O)](ClO4)2 (4) and [Co(L(5))(H2O)](ClO4)2 (5), derived from the pentadentate ligands L(1)-L(5), which are the 1 : 2 condensation products of triamines and 2-acetylpyridine or 2-pyridinecarboxaldehyde (6-methyl-2-pyridinecarboxaldehyde). X-ray crystallography reveals exclusive selectivity of the acyclic Schiff dibasic form of the ligands over the heterocyclic analogues, and this selectivity is found to be insensitive to the oxidation state of cobalt. Other first row transition metals have been characterized in either form of the ligands in their complexes but it is specific for cobalt established in the present study. The pronounced effect of the methyl substitutions is observed from their crystal structures; substitution at imine-C does not have any significant influence on the peroxo-bridging but substitution at sixth position of pyridyl ring prevents the formation of peroxo-bridging, and both the steric and electronic factors play vital roles on such chemical diversity. All the complexes show the phenoxazinone synthase mimicking activity and the comparative catalytic activity has been explored. Although electrochemical behaviors of all the complexes are very similar, their relative catalytic activity mimicking the function of phenoxazinone synthase arises from the electronic and steric factors of the methyl substitution.

Covalent Co–O–V and Sb–N Bonds Enable Polyoxovanadate Charge Control

“…The Co2–N bonds can be divided into two groups: four shorter bonds to N atoms in the basal plane of the octahedron [2.154(7)–2.190(8) Å] and two longer bonds to the apical atoms of the polyhedron [2.221(7)–2.228(7) Å] (Table S4 in the Supporting Information), but these values are still comparable with literature data. 11,17−21 The binuclear complex can be formulated as [Co 2 (tren)(teta) 2 ] 4+ , and the connection mode observed here is unique.…”

“…The Co–N bonds between 2.128(8) and 2.162(9) Å (Table S4 in the Supporting Information) are in line with the previously reported data. 11,17−21 …”

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.…”

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

“…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.…”