Synthesis and evaluation of catecholase activities of metal complexes of 1,4-substituted piperazine Mannich base of 4-acetamidophenol

The synthesis and characterisation including H-1 and C-13 NMR spectroscopy of a Mannich base 1,4-di-(5-acetamido-2-hydroxybenzyl)piperazine is herein reported. The Mannich reaction leading to the formation of the ligand took place at both ends of piperazine. Four metal complexes [Cu(II) and Fe(III)] including those bearing thiocyanate groups (SCN-) in N- and S-bonding modes have been studied for their abilities to mimic catecholase oxidase. All the metal complexes are catalytically active with the highest turnover rate (k(cat)) recorded for complex 3. The catalytic process as monitored by H-1 NMR spectroscopy (isolation of 3, 5-DTBQ) and iodometric titration revealed the formation of H2O2 and thus implied that the mechanism of oxidation is through the formation of a semiquinolate species.