Reaction of (μ-oxo)diiron(III) core with CO2 in N-methylimidazole:: Formation of mono(μ-carboxylato)(μ-oxo)diiron(III) complexes with N-methylimidazole as ligands

Several iron(III) complexes with N-methylimidazole (N-Melm) as the ligand have been synthesized by using N-Melm as the solvent. Under anaerobic conditions, [Fe(N-Melm)(6)](ClO4)(3) (1) reacts with stoichiometric amounts of water in N-Melm to afford the (mu-oxo)diiron(III) complex, [Fe-2(mu-O)(N-Melm)(10)](ClO4)(4) (3). Exposure of a solution of 3 in N-Melm to stoichiometric and excess CO2 gives rise to the (mu-oxo)(mu-carboxylato)diiron(III) species [Fe-2(mu-O)(mu-HCO2)(N-Melm)(8)](ClO4)(3) (4) and the methyl carbonate complex [Fe-2(mu-O)(mu-CH3OCO2)(N-Melm)(8)](ClO4)(3) (5), respectively. Formation of the formato-bridged complex 4 upon fixation of CO2 by 3 in N-Melm is unprecedentated. Methyl transfer from N-Melm to a bicarbonato-bridged (mu-oxo)diiron(ill) intermediate appears to give rise to 5. complex 3 is a good starting material for the synthesis of (mu-oxo)mono(mu-carboxylato)diiron(III) species [Fe-2(muO)(mu-RCO2)(N-Melm)(8)](ClO4)(3) (where R = H (4), CH3 (6), or C6H5 (7)); addition of the respective carboxylate ligand in stoichiometric amount to a solution of 3 in N-Melm affords these complexes in high yields. Attempts to add a third bridge to complexes 4, 6, and 7 to form the (mu-oxo)bis(mu-carboxylato)diiron(III) species result in the isolation of the previously known triiron(III) mu-eta(3)-oxo clusters [{Fe(mu-RCO2)(2)(N-Melm)}(3)O](ClO4) (8). The structures of 3, 4, 6, and 7 allow one, for the first time, to inspect the various features of the {Fe-2(mu-O)(mu-RCO2)}(3+) moiety with no strain from the ligand framework.