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

Abstract

The synthesis and characterisation including ${}^1H$ and ${}^{13}C$ 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 ligandtook place at both ends of piperazine. Four metal complexes [Cu(II) and Fe(III)] including those bearing thiocyanategroups (SCN–) in N- and S-bonding modes have been studied for their abilities to mimic catecholase oxidase. All themetal complexes are catalytically active with the highest turnover rate ($k_{cat}$) recorded for complex 3. The catalyticprocess as monitored by ${}^1H$ NMR spectroscopy (isolation of 3, 5-DTBQ) and iodometric titration revealed the formationof $H_2;O_2$ and thus implied that the mechanism of oxidation is through the formation of a semiquinolate species.