STRUCTURAL CHARACTERIZATION OF VERDOHEME ANALOGS - IRON COMPLEXES OF OCTAETHYLOXOPORPHYRIN

The verdohemes are shown to contain the planar, tetradentate oxoporphyrin structure. Structural studies of paramagnetic {(OEOP)FeIIICl2}, where OEOP is the monoanion of octaethyloxoporphyrin, by H-1 NMR spectroscopy and X-ray crystallography reveal that the iron is six-coordinate and high-spin (S = 5/2). The iron resides in the plane of the oxoporphyrin and is coordinated by two equivalent axial chloride ligands. Paramagnetic {(OEOP)Fe(II)Cl} contains a five-coordinate iron which is also high-spin (S = 2). The iron is 0.69 angstrom out of the porphyrin plane and bound to a single axial chloride. The average Fe-N distance increases from 1.964 angstrom in the iron(III) complex to 2.094 angstrom in the iron(II) complex. {(OEOP)FeIIICl2} was obtained by treatment of (OEP)Fe(py)2 (OEP is the dianion of octaethylporphyrin) with dioxygen in the presence of ascorbic acid to form the verdohemochrome [(OEOP)FeII(PY)2]Cl, which was subsequently reacted with hydrogen chloride in air. Reduction of {(OEOP)FeIIICl2} with sodium dithionite yields air-sensitive {(OEOP)Fe(II)Cl}. When {(OEOP)Fe(II)Cl} is dissolved in pyridine, [(OEOP)FeII(py)2]Cl is reformed.