MODELS OF THE OXIDIZED FORMS OF POLYIRON OXO PROTEINS - SYNTHETIC ROUTES TO (MU-OXO)BIS(MU-CARBOXYLATO)DIIRON(III) COMPLEXES WITH NEUTRAL MONODENTATE AND BIDENTATE CAPPING LIGANDS

Two (mu-oxo)bis(mu-carboxylato)diiron(III) complexes with neutral monodentate and bidentate terminal ligands have been prepared that incorporate features of the diiron oxo centers in the non-heme iron proteins hemerythrin (Hr) and the B2 subunit of ribonucleotide reductase (RRB2) that were not previously modeled. [Fe2O(OH2)2(O2CCH2Cl)2(bpy)2](NO3)2 (1) and [Fe2O(CH3OH)2(O2CCH3)2(BIPhMe)2](NO3)2 (2) were synthesized from the appropriate basic iron carboxylate, ferric nitrate and the bidentate nitrogen ligand bpy or BIPhMe. The molecular structures, as determined by X-ray crystallography, and the electronic spectral, Mossbauer and magnetic properties of 1 and 2 reproduce many of the physical properties of the met forms of Hr and RRB2. A singly-bridged (mu-oxo)diiron(III) complex, [Fe2O(NO3)4(bpy)2] (3), was also prepared from ferric nitrate and bpy. The chelating bpy and nitrate ligands afford seven-coordinate ferric centers in the centrosymmetric compound. Complex 3 serves as a synthon for the (mu-oxo)bis(A-carboxylato)diiron(III) core, for the reaction of 3 with excess chloroacetic acid gives 1.