Synthesis and structures of dimeric iron(III)-Oxo and -imido complexes containing intramolecular hydrogen bonds

Hydrogen bonding networks proximal to metal centers are emerging as a viable means for controlling secondary coordination spheres. This has led to the regulation of reactivity and isolation of complexes with new structural motifs. We have used the tridenate ligand bis[(N′-tert-butylureido)-N-ethyl]-N-methylaminato ([H21]2−) that contains two hydrogen bond donors to examine the oxidation of the FeII–acetate complex, [FeIIH21(η2-OAc)]− with dioxygen, amine N-oxides, and xylyl azide. A complex with FeIII–O–FeIII core results from the oxidation with dioxygen and amine N-oxides, in which the oxo ligand is involved in hydrogen bonding to the [H21]2− ligand. A distinctly different hydrogen bonding network was found in FeIII dimer isolated from the reaction with the xylyl azide: a rare FeIII–N(R)–FeIII core was observed that does not have hydrogen bonds to the bridging nitrogen atom. The intramolecular H-bond networks within these dimers appear to adjust to the presence of the bridging species and rearrange to its size and electron density.