Structure and oxygenase activity of the iron(ii) complex with pyridylcarboxamide ligand

A reaction of Fe(ClO₄)₂·6H₂O or Fe(OTf)₂(MeCN)₂ with one equivalent of the tetradentate ligand bis(2-pyridyl)methyl-2-pyridylcarboxamide (Py₂CHNHCOPy, tpcaH) furnished dimeric iron(II) complexes [Fe(tpcaH)]₂X₄ (X = ClO₄ ^? (1a), OTf^? (1b)). According to the X-ray diffraction data for the complex 1a, each iron atom is bound to the two pyridyl fragments of one ligand and the pyridylcarboxamide pair of the other one. Complex 1a is a dimer in the crystalline state, while in MeCN solution according to the mass spectrometric data with the electrospray ionization, ¹H NMR spectroscopic data, and quantum chemical calculations, it is apparently in the equilibrium with monomers of different structures. Complex 1 catalyzes selective oxidation of saturated hydrocarbons with hydrogen peroxide presumably involving the perferryl intermediate, which has an N,N,O-facial coordination of potentially tetradentate ligand tpcaH structurally modeling the 2-histidine-1-carboxylate-facial triad of the nonheme oxygenases.