Reaction of ((mu)-Oxo)diiron(III) Core with CO2 in N-Methylimidazole: Formation of Mono((mu)-carboxylato)((mu)-oxo)diiron(III) Complexes with N-Methylimidazole as Ligands

Several iron(lll) 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](C104)3 (1) reacts with stoichiometric amounts of water in N-Melm to afford the ((mu)-oxo)diiron(lll) complex, [Fe2(-O)(N-Melm)io](C104)4 (3). Exposure of a solution of 3 in N-Melm to stoichiometric and excess CO2 gives rise to the (-oxo)(-carboxylato)diiron(lll) species [Fe2(-0)(HC02)(N-Melm)8](C104)3 (4) and the methyl carbonate complex [Fe2-0)-CH30C02)(N-Melm)8](C104)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 (-oxo)diiron(lll) intermediate appears to give rise to 5. Complex 3 is a good starting material for the synthesis of (-oxo)mono(-carboxylato)diiron(lll) species [Fe2(0)-RC02)(N-Melm)8](C104)3 (where R = H (4), 1 (6), or C6H6 (7)); addition of the respective carboxylate ligand in stoichiometric amount to a solution of 3 in NMelm affords these complexes in high yields. Attempts to add a third bridge to complexes 4, 6, and 7 to form the (-oxo)bis(-carboxylato)diiron(lll) species result in the isolation of the previously known triiron(lll)(mu) clusters [{Fe(-RC02)2(N-elm)}30](C104) (8). The structures of 3, 4, 6, and 7 allow one, for the first time, to inspect the various features of the {Fe2(-0)(-RC02)} moiety with no strain from the ligand framework.