Mononuclear iron complexes relevant to nonheme iron oxygenases. Synthesis, characterizations and reactivity of Fe-Oxo and Fe-Peroxo intermediates.

The new ligand L(6)(2)4E (N,N,N',N'-tetrakis(5-ethyl-2-pyridylmethyl)ethane-1,2-diamine) was designed as a more robust analog of TPEN (N,N,N',N'-tetrakis(2-pyridylmethyl)ethane-1,2-diamine) for which the ability at stabilizing high valent Fe-Oxo and Fe-(hydro)peroxo has been reported. With respect to the latter, the pyridyl beta-substituents in L(6)(2)4E do not modify the Fe coordination chemistry. From the Fe(II) precursor, FeO and Fe(III)-(hydro)peroxo intermediates are prepared using the same synthetic methods as those reported for the TPEN analogs. The spectroscopic characteristics of all L(6)(2)4E-Fe complexes are very similar to their TPEN analog. However, (L(6)(2)4E)FeO has a greater lifetime than that of (TPEN)FeO. This can be explained by a restricted bimolecular autodegradation due to the bulkiness provided by the ethyl substituents. Regarding small organic molecule oxidation, (L(6)(2)4E)FeO and (L(6)(2)4E)FeOOH exhibit behaviours that seem to be general for the complexes built with ligands of the TPEN family: FeO appears to be efficient to epoxidize olefins, whereas FeOOH hydroxylates the aromatic ring of anisole with efficacy.