Mono and tri-nuclear cobalt(III) complexes with sterically constrained phenol based N2O2 ligand: Synthesis, structure and catechol oxidase activity

Mono and tri- nuclear Co(III) complexes, [Co-3(OMe)(4)L-2]ClO4 (1) and [CoL(acac)] (2) have been synthesized using sterically constrained tetradentate ligand N,N-/-dimethyl-N,N-/-bis(2-hydroxy-3,5-dimethylbenzyl)-ethylenediamine (H2L) with varying reaction condition. All complexes have been characterized by single crystal X-ray diffractometer and various spectroscopic tools. Complex 1 is tri-nuclear methoxo and phenoxo bridged cobalt complex with Co-III - Co-III - Co-III linear core, whereas complex 2 is mononuclear mixed ligand octahedral Co(III) complex. Both complexes show catechol oxidase activity in methanol as monitored by the UV-Vis spectroscopy of the aerial oxidation of 3,5-DTBC to 3,5-DTBQ. The kinetic parameters have been determined using Michaelis-Menten approach. The complexes are efficient catalysts with high turnover numbers 3.32 x 10(3) h(-1) and 2.19 x 10(3) h(-1) for 1 and 2, respectively. Mechanistic investigations of the catalytic behaviour by ESI-MS spectra and estimation of hydrogen peroxide formation indicates that the catalytic reaction occurs through the reduction of Co(III) to Co(II). (C) 2020 Elsevier Ltd. All rights reserved.