Synthesis, structure and catecholase activity of a trinuclear mixed valence cobalt complex

•A new mixed valent cobalt complex [L3CoIICoIII2(CH3COO)(OCH3)] (2) has been synthesized and characterized.•2 is an efficient bio-functional model of catechol oxidase.•2 takes 10 min for complete conversion of 3,5-DTBC to 3,5-DTBQ.•In solution, 2 may dissociate into a mononuclear moietiy which act as the catalytically active species.•A metal centric SET mechanism has been proposed for catecholic oxidation by 2. A trinuclear mixed valence cobalt complex, [L3CoIICoIII2(CH3COO)(OCH3)] (2), has been synthesized using a Schiff base ligand (H2L, 1). The ligand was prepared via 1:1 condensation of 3-Chloro salicylaldehyde and 3-Amino-1-propanol in methanol. The structure of 2 has been elucidated by single crystal X-ray crystallography. Comparing each set of the corresponding data of bond lengths and bond angles, presence of two different oxidation states (+2 and +3) of the cobalt metal ions was understood. Again the occurrence of mixed valence has been confirmed by X-ray photoelectron spectroscopy (XPS) study of 2. Interestingly, 2 acted as an efficient bio-mimic of catechol oxidase toward oxidation of 3,5-di‑tert-butyl catechol (3,5-DTBC) to 3,5-di‑tert-butyl quinone (3,5-DTBQ). Two different solvents, methanol (CH3OH) and acetonitrile (CH3CN), have been utilized as media for exploring catecholase activity of 2 and acetonitrile was observed to be a better medium since furnished greater turn-over number. 1HNMR spectroscopy suggests completion of the oxidation process within just ten minutes in acetonitrile. The ESI-MS spectrum of the substrate-catalyst mixtures in acetonitrile confirmed formation of Co(III)-3,5-DTSQ (3,5-DTSQ = 3,5-di‑tert butyl semiquinone) intermediates in the time scale of mass spectrum which could stand as a supporting evidence for the catalytic function of 2. However, all the substrate bound intermediates observed are mononuclear which indicates that the complex probably undergoes a dissociation in acetonitrile to generate mononuclear fragments for binding the substrate. Thus, on the basis of ESI-MS, 2 may be suggested as a pre-catalyst. [Display omitted]