Mixed valence trinuclear cobalt (II/III) complexes: Synthesis, structural characterization and phenoxazinone synthase activity

Three new mixed valence trinuclear Co(II/III) compounds [Co3L2(mu(2)-C6H5CO2-)(2)(CH3CN)(2)] (ClO4-)(2)center dot(CH3CN)(3) (1) [Co3L2R(mu(2)-C6H5CO2-)(2)(C6H5CO2-)(2)]center dot(CH3CN)(2) (2) and [Co3L2R(mu(2)-C6H5CH=CH CO2-)(2) (C6H5CH=CH CO2-)(2)]center dot((CH3)(2)CO)(2) (3) have been synthesized by reacting the di-Schiff base ligand [H2L] or its reduced analog [H2LR] (where H2L = N,N'-bis(salicylidene)-1,3-propanediamine) and (H2LR = N,N'-bis(2-hydroxybenzy1)-1,3-propanediamine) with cobalt perchlorate hexahydrate and sodium benzoate or sodium cinnamate. The complexes have been characterized by IR, UV-Vis and single crystal X-ray diffraction analyses. All the complexes are linear trinuclear species [Co-III-Co-II-Co-III] in which two terminal octahedral (CoN2O2)-N-III cores coordinate to the central octahedral Co-II ion through mu(2)-phenoxido oxygen atom and the bridging carboxylato ions. In addition, the complexes (2 and 3) derived from reduced Schiff base ligand have, rather unusually, a terminally coordinated carboxylato ion to Co-III, which is acetonitrile molecule in case of complex (1) with unreduced ligand. Complex 2 has been found to be an excellent functional model for the phenoxazinone synthase activity, in the aerial oxidation of 2-aminophenol to the corresponding 2-aminophenoxazine-3-one chromophore in acetonitrile solvent medium. Detailed kinetic data analysis of this oxidation reaction reveals a fairly high phenoxazinone synthase activity of 2 with k(cat) = 153.60 h(-1). (C) 2017 Elsevier Ltd. All rights reserved.