Catalytic action of the iron(II) complexes of 8-methyl-1,4-bis(2-pyridylmethyl)-1,4,8-triazacycloundecane and 1-methyl-5,9-bis(2-pyridylmethyl)-1,5,9-triazacyclododecane

The kinetics and mechanism of the catalatic decomposition of hydrogen perox ide by the iron(II) complexes of the macrocyclic ligands 8-methyl-1,4-bis(2 -pyridylmethyl)-1,4,8-triazacycloundecane (L-1) and 1-methyl-5,9-bis(2-pyri dylmethyl)-1,5,9-triazacyclododecane (L-2) have been investigated at neutra l pH (in phosphate buffer). The oxidation of two equivalents of iron(II) to iron(III) by one equivalent of hydrogen peroxide was observed by spectroph otometric titration. The catalysed decomposition of hydrogen peroxide by ir on(III) complex was observed and studied. During the catalytic process a re active intermediate was scavenged by 2,2'-azinobis(3-ethylbenzothiazoline-6 -sulfonate) (ABTS), but not by bromide ion, indicating that the strongly ox idative intermediate is not the hydroxyl radical, and supporting the altern ative possibility, a high valent iron-oxo species. Stopped-flow and steady- state kinetic experiments provide further evidence for the detailed mechani sm suggested.