Two Cobalt(III) Schiff Base Complexes of the Type [Co(ABC)(DE)X]: Facile Synthesis, Characterization, Catechol Oxidase and Phenoxazinone Synthase Mimicking Activity

Abstract

Two new mononuclear cobalt(III) Schiff base complexes with azide or thiocyanate [Co(L 1 )(L')(N 3 )] (1) and [Co(L 2 )(L")(NCS)] (2) {where HL 1 = 2((2(piperidin-1-yl)ethylimino)methyl)-6-ethoxyphenol, HL 2 = 2-((3(dimethylamino)propylimino)methyl)-6-methoxyphenol, HL' = 1-acetyl-2-naphthol and HL" = 2,4-pentane-dione} have been synthesized and characterized by single crystal X-ray diffraction studies. Both complexes may be represented by a general formula: [Co(ABC)(DE)X], where ABC, DE and X represent tridentate, bidentate and monodentate ligands respectively. Both complexes are reactive towards the aerial oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) and oaminophenol (OAPH), and kinetics of the reactions are monitored spectrophotometrically. Analyses of the kinetic data reveal that complex 2 is better catalyst than complex 1 for both oxidation reactions. Tentative mechanistic implications of the catalytic oxidation reactions are also discussed. Mechanistic investigations of the catalytic behaviors indicate that the oxidation reactions proceed through catalyst-substrate intermediates. Results and discussion SynthesisThe Schiff base ligand, HL 1 , was synthesized by the 1:1 condensation of 1-(2-aminoethyl)piperidine with 3-ethoxysali-[a] K.

Structure-directing role of CH⋯X (X = C, N, S, Cl) interactions in three ionic cobalt complexes: X-ray investigation and DFT study using QTAIM Vr predictor to eliminate the effect of pure Coulombic forces

“…In the high-energy region, complex 1 showed intense absorption bands around 243–275 nm, corresponding to π–π* transitions. 28,112,113 Broad absorption bands at 314 nm (for 2 ) and 388 nm (for 3 ) were also observed, which were consistent with the LMCT band. 114–116 The electronic absorption spectra of all three complexes in acetonitrile medium showed d–d transition bands around 426 nm (for 1 ), 404 nm (for 2 ), and 654 nm (for 3 ), as expected for a low spin cobalt( iii ) complex in an octahedral geometry.…”

“…25,26 Focusing on cobalt(III) complexes of N, O donor Schiff bases, many studies have been reported in the literature regarding their biomimetic catalytic activity, such as phenoxazinone synthase mimicking and catechol oxidase mimicking activity. [27][28][29][30][31] It is, however, true that cobalt has not been found in the active site structure of any metallo-oxidase yet, probably because of the inert character of cobalt(III), but this inert character of cobalt(III) attracts the interests of coordination chemists to synthesize biomimetic catalysts with cobalt(III), so that the intermediate species formed in the catalytic cycle could be identied easily and the mechanistic pathway of a catalytic reaction could be gured out. 29 The exploration of opto-electronic properties of cobalt(III) complexes of Schiff base ligands is also a growing research topic owing to the low cost and good availability of the metal sources and the structural exibility and stability of the ligands.…”

One pot synthesis of two cobalt(iii) Schiff base complexes with chelating pyridyltetrazolate and exploration of their bio-relevant catalytic activities

“…A detailed literature survey with cobalt based model complexes for catechol oxidase and phenoxazinone synthase mimicking activities has shown that several factors may affect their catalytic activity, such as the oxidation state of the metal, coordination geometry around the metal center, metal–metal distance, ligand flexibility, exogenous bridging ligand etc. 47,48 All these cobalt based model complexes showing catechol oxidase and phenoxazinone synthase mimicking activity are gathered in Tables 8 and 9 respectively along with several kinetic parameters such as K M , V max and k cat . As the turnover numbers ( k cat values) of both complexes fall in between the range, they may be considered as moderate catalysts.…”

Formation of H-bonding networks in the solid state structure of a trinuclear cobalt(iii/ii/iii) complex with N2O2 donor Schiff base ligand and glutaric acid as bridging co-ligand: synthesis, structure and DFT study

“…1,33–45 They have also been used to mimic several enzymes. 38–45 These types of promising applications of salen type complexes have attracted our attention for the synthesis of transition metal compounds of salen type N 2 O 2 donor Schiff base ligands.…”