Diiron(II) μ-Aqua-μ-hydroxo Model for Non-Heme Iron Sites in Proteins

We have synthesized a diiron(II) complex with a novel aqua−hydroxo bridging motif, [Fe2(μ-H2O)(μ-OH)(TPA)2](OTf)3 (1). This is a new member of the diiron diamond core family. The complex is stable in solution in nonpolar solvents as well as in the solid state. Two high-spin iron(II) sites are antiferromagnetically coupled (J = −9.6 cm-1). The drastic difference of ca. 1 V in the redox potential between complex 1 and its bis(hydroxo)-bridged analogue Fe2(OH)2(TPA)3+ is accompanied by only a moderate difference in the dioxygen reactivity. This observation is consistent with the inner-sphere mechanism of iron(II)−dioxygen association rather than the outer-sphere electron transfer.