Synthesis and spectroscopic studies of non-heme diiron(III) species with aterminal hydroperoxide ligand: Models for hemerythrin

Two compounds, [Fe-2(mu -OH)(mu -Ph(4)DBA)(TMEDA)(2)(OTf)] (4) and [Fe-2(mu -OH)(mu -Ph(4)DBA)(DPE)(2)(OTf)] (7), where Ph(4)DBA(2-) is the dinucleati ng bis(carboxylate) ligand dibenzofuran-4,6-bis(diphenylacetate), have been prepared as synthetic models for the dioxygen-binding non-heme diiron prot ein hemerythrin (Hr). X-ray crystallography reveals that, in the solid stat e, these compounds contain the asymmetric coordination environment found at the diiron center in the reduced form of the protein, deoxyHr. Mossbauer s pectra of the models (4, delta = DeltaE(Q) = 2.87(2) min s(-1); 7, delta (a v), = 1.23(1), DeltaE(Qav) = 2.79(1) mm s(-1)) and deoxyHr (delta = 1.19, D eltaE(Q) = 2.81 s(-1)) are also in good agreement. Oxygenation of the diiro n(II) complexes dissolved in CH2Cl2 containing 3 equiv of N-MeIm (4) or nea t EtCN (7) at -78 'C affords a red-orange solution with optical bands at 33 6 nm (7300 M-1 cm(-1)) and 470 nm (2600 M-1 cm(-1)) for 4 and at 334 run (6 400 M-1 cm(-1)) and 484 nm (2350 M-1 cm(-1)) for 7. These spectra are remar kably similar to that of oxyHr, 330 nm (6800 M-1 cm(-1)) and 500 ran (2200 M-1 cm(-1)). The electron paramagnetic resonance (EPR) spectrum of the cryo reduced, mixed-valence dioxygen adduct of 7 displays properties consistent with a (mu -oxo)diiron(II,III) core. An investigation of 7 and its dioxygen -bound adduct by extended X-ray absorption fine structure (EXAFS) spectrosc opy indicates that the oxidized species contains a (mu -oxo)diiron(III) cor e with iron-ligand distances in agreement with those expected for oxide, ca rboxylate, and amine/hydroperoxide donor atoms. The analogous cobalt comple x [Co-2(mu -OH)(mu -Ph(4)DBA)-(TMEDA)(2)(OTf)] (6) was synthesized and stru cturally characterized, but it was unreactive toward dioxygen.