Synthesis and spectroscopic studies of non-heme diiron(III) species with a terminal hydroperoxide ligand: models for hemerythrin.

Two compounds, [Fe2(μ-OH)(μ-Ph4DBA)(TMEDA)2(OTf)] (4) and [Fe2(μ-OH)(μ-Ph4DBA)(DPE)2(OTf)] (7), where Ph4DBA2- is the dinucleating bis(carboxylate) ligand dibenzofuran-4,6-bis(diphenylacetate), have been prepared as synthetic models for the dioxygen-binding non-heme diiron protein hemerythrin (Hr). X-ray crystallography reveals that, in the solid state, these compounds contain the asymmetric coordination environment found at the diiron center in the reduced form of the protein, deoxyHr. Mossbauer spectra of the models (4, δ = 1.21(2), ΔEQ = 2.87(2) mm s-1; 7, δav = 1.23(1), ΔEQav = 2.79(1) mm s-1) and deoxyHr (δ = 1.19, ΔEQ = 2.81 mm s-1) are also in good agreement. Oxygenation of the diiron(II) complexes dissolved in CH2Cl2 containing 3 equiv of N-MeIm (4) or neat EtCN (7) at −78 °C affords a red-orange solution with optical bands at 336 nm (7300 M-1 cm-1) and 470 nm (2600 M-1 cm-1) for 4 and at 334 nm (6400 M-1 cm-1) and 484 nm (2350 M-1 cm-1) for 7. These spectra are remarkably similar to that of oxyHr...