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

The macrocyclic proligand [H4L][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 [H2L]. Metallation of [H2L] with iron(II) chloride proceeds rapidly to form the macrocyclic complex, [FeIIICl(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, [FeIIICl(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 [FeIIICl(L)]. The incorporation of four mixed or hybrid pyridinium amidate/amidate donors into a macrocyclic ligand leads to a superior iron catalyst that resists acid-induced demetallation and rapidly catalyses hydrogen peroxide oxidation of the surrogate organic pollutant orange II in water at pH 7 and at ambient temperature.image

Automated summary

It was found that the macrocyclic complex [FeIIICl(L)] with two pyridinium groups showed high oxidation catalytic activity at pH 7, and it exhibited high stability towards acid-promoted demetallation at pH 5 or above.