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

Abstract Mono and tri- nuclear Co(III) complexes, [Co3(OMe)4L2]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 CoIII – CoIII – CoIII 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 × 103 h-1 and 2.19 × 103 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).