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.