Dinuclear mixed valence cobalt(II/III) and hetero-tetranuclear cobalt(III)/Na complexes with a compartmental ligand: Synthesis, characterization and use as catalysts for oxidative dimerisation of 2-aminophenol

Abstract

A N2O4 donor compartmental reduced Schiff base ligand, H2L [(2,2-dimethyl-1,3-propanediyl)bis(iminomethylene)bis(6-methoxyphenol)], obtained on 1:2 condensation of 2,2-dimethyl-1,3-propanediamine with ortho-vanillin followed by reduction with NaBH4 in methanol solution, has been used to prepare two cobalt complexes, [(N3)CoIIIL(µ-OAc)CoII(N3)] (1) and [(μ-N3)2{(AcO)CoIIILNa(CH3OH)}2]·2CH3OH (2). Complex 1 is a dinuclear mixed valence cobalt(III)/cobalt(II) complex with CoIIIO2CoII core. Complex 2, on the other hand, is a tetranuclear cobalt(III)/sodium complex with CoO2Na(N3)2NaO2Co core. Formation of complex 1 or 2 is mainly governed by the amount of cobalt(II) precursors present in the reaction mixture. Each complex has been characterized by elemental and spectral analysis. X-ray diffraction analysis has confirmed their structures. Complex 1 crystallized in a chiral space group Pna21 where both the cobalt(III) and cobalt(II) centers adopt six-coordinate distorted octahedral geometry with cobalt(III) and cobalt(II) centers residing respectivelyat inner N2O2 and outer O4 cavities of the reduced Schiff base. Complex 2 crystallized in triclinic system with P1-space group, where both cobalt(III) and sodium centers adopt distorted octahedral geometry. Oxidation states of cobalt centers have been confirmed by bond length consideration, BVS calculations as well as from room temperature magnetic moment measurement. Both complexes 1 and 2 show phenoxazinone synthase mimicking activity with kcat values 250.21 and 493.73 h−1 respectively.