Manganese(ii) complex of an oxygen–nitrogen donor Schiff base ligand showing efficient catechol oxidase activity: synthesis, spectroscopic and kinetic study

Abstract

Tridentate O,N,O-donor Schiff base ligand (E)-1-(2-hydroxybenzylidene)semicarbazide (H₂L¹) and its Mn(II) complex have been synthesized. Both the ligand and the complex have been characterized by analytical and spectroscopic techniques. X-ray crystal structure determination of the Mn(II) complex shows that the Mn(II) atom is in a distorted octahedral environment and there are two crystallographically different manganese atoms in the unit cell. The Mn(II) complex shows very high catalytic activity for catechol oxidation (k_cat = 3.10 × 10⁶ h⁻¹, k_cat/K_M = 3.25 × 10⁸ h⁻¹ M⁻¹), which is the highest catalytic efficiency for catechol oxidation by a manganese complex reported in the literature. The probable mechanism of the catalytic reaction is explored using ESI-MS and EPR spectroscopy.