Formation and stabilization of five-coordinate iron(II) verdoheme analogues by axial weakly coordinating anion ligation. X-ray crystal structures of [(OEOPFe)2O](X)2 (X = AsF6, SbF6)

The effect of weakly coordinating anions, AsF6-andSbF6-, as axial ligands on the formation and coordination chemistry of verdoheme analogues have been examined. Two new five-coordinate and stable iron(II) verdoheme analogues, [OEOPFeIIX], where OEOP is the monoanion of octaethyloxoporphyrin and X = AsF6 and SbF6, have been isolated. The compounds have been characterized by different spectroscopic methods as well as elemental analysis. 1H NMR spectroscopy and magnetic moment measurements show that the [OEOPFeIIX] are paramagnetic and iron is five-coordinate. Exposure of dichloromethane solutions of [OEOPFeIIX] (X = AsF6 (2), SbF6 (3)) to dioxygen result in their transformation into the μ-oxo bridged compounds, [(OEOPFe)2O](X)2 (X = AsF6 (4), SbF6 (5)). The structures of 4 and 5 have been determined by X-ray diffraction analysis, both are structurally similar with a P21/c space group in the monoclinic crystal system.

Graphical abstractThe synthesis of two new verdoheme derivatives with weakly coordinating anions, [OEOPFeIIX] (X = AsF6, SbF6), have been reported. Exposure of dichloromethane solutions of [OEOPFeIIX] (X = AsF6, SbF6) to dioxygen result in their transformation into the μ-oxo bridged compounds, [(OEOPFe)2O](X)2 (X = AsF6, SbF6). The difference on reactivity of the [OEOPFeIICl] species and that of [OEOPFeIIX] toward O2 is remarkable.Figure optionsDownload full-size imageDownload as PowerPoint slide