The Coordination Chemistry of FeCl3 and FeCl2 to Bis[2-(2,3-dihydroxyphenyl)-6-pyridylmethyl](2-pyridylmethyl)amine: Access to a Diiron(III) Compound with an Unusual Pentagonal-Bipyramidal/Square-Pyramidal Environment

Coordination of FeCl3 to the title ligand yields a mononuclear iron(III) complex 1, which was characterized by spectroscopic techniques and X‐ray diffraction. The ligand is (κ3‐N) tridentate and the metal, which lies in a pseudo‐octahedral environment, is bound to a phenolate group from the catechol substituent. The dichloroiron(II) complex 2 was easily obtained by metalation of the ligand with FeCl2 and characterized by various spectroscopic techniques. In their cyclic voltammograms both 1 and 2 display the same reversible FeII/FeIII wave at E1/2=10 mV (vs. SCE). Reduction of compound 1 with Zn/Hg yields 2′, which displays identical properties to 2. Taken together, these findings indicate that in spite of the different oxidation state of the metal in 2, no major geometrical/structural change is observed at the metal center with respect to 1. The reaction of 2 with dioxygen in the absence of organic substrates proceeds extremely rapidly and yields compound 3, which is a diiron(III) derivative whose X‐ray crystal structure is also reported. The possibility of a radical‐based mechanism is discussed. Compound 3 displays an unusual geometry: one iron(III) center is seven‐coordinate, whereas the other lies in a square‐pyramidal environment. The two iron atoms are bridged by the catecholato substituents. To the best of our knowledge, 3 is the first example of a seven‐coordinate iron(III) derivative with tris(2‐pyridylmethyl)amine ligands. Coordination of FeCl3 to the title ligand occurs at the nitrogen‐containing site to yield 1. The dichloroiron(II) derivative 2 can be accessed directly from the free ligand and FeCl2, or alternatively by reduction of the iron(III) derivative. Compound 2 reacts instantaneously with dioxygen (see picture) to yield 3, a diiron(III) derivative with an unusual pentagonal‐bipyramidal/square‐pyramidal core, by a mechanism that is likely to be radical based.