Synthesis and Structures of Dimeric Iron(III)-Oxo and -Imido Complexes Containing Intramolecular Hydrogen Bonds

Abstract

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 ([H(2)1](2-)) that contains two hydrogen bond donors to examine the oxidation of the Fe(II)-acetate complex, [Fe(II)H(2)1(η(2)-OAc)](-) with dioxygen, amine N-oxides, and xylyl azide. A complex with Fe(III)-O-Fe(III) core results from the oxidation with dioxygen and amine N-oxides, in which the oxo ligand is involved in hydrogen bonding to the [H(2)1](2-) ligand. A distinctly different hydrogen bonding network was found in Fe(III) dimer isolated from the reaction with the xylyl azide: a rare Fe(III)-N(R)-Fe(III) 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.

Figure 1

Molecular structure of [(Fe^IIIH₂1)₂(μ-O)]. The ellipsoids are drawn at the 50% probability level. Non-urea hydrogen atoms and the methyl groups of the tert-butyl functionalities have been removed for clarity.

Figure 2

Molecular structure of [(Fe^IIIH₂1)₂(μ-N-xylyl)]. The ellipsoids are drawn at the 50% probability level. Non-urea hydrogen atoms and the methyl groups of the tert-butyl functionalities have been removed for clarity.

Scheme 1

Conditions: (a) 0.5 equiv. TMANO or 0.25 equiv. O₂, DMA, rt, Ar; (b) 0.5 equiv. N₃Xylyl, DMA, rt, Ar.