An Iron Macrocyclic Complex Containing Four "Hybrid" Pyridinium Amidate/Amidate N-Donors as a Catalyst for Oxidations with Hydrogen Peroxide.

The macrocyclic proligand [H4 L][OTf]2 , which contains four carboxamide functions and two conjugated pyridinium groups, is easily deprotonated by the weak base sodium acetate to give the corresponding neutral proligand [H2 L]. Metallation of [H2 L] with iron(II) chloride proceeds rapidly to form the macrocyclic complex, [FeIII Cl(L)]. This is an effective catalyst for the oxidation of the organic dye orange II by hydrogen peroxide in aqueous solution, and the kinetic parameters for this reaction have been determined. In striking contrast to an analogous iron-TAML complex that contains two phenyl groups in place of the two pyridinium groups, [FeIII Cl(L)] is a very active oxidation catalyst at pH 7 and is also highly stable towards acid-promoted demetallation at pH 5 or above. The results show that the two pyridinium groups bring greatly enhanced catalytic properties to [FeIII Cl(L)].