Synthesis, Characterization, and Reactivity of Iron Trisamidoamine Complexes That Undergo Both Metal- and Ligand-Centered Oxidative Transformations

Functional systems that combine redox-active metals and noninnocent ligands are no longer rare chemical oddities; they are instead emerging as significant components of catalytic and enzymatic reactions. The present work examines the synthetic and functional aspects of iron compounds ligated by a family of new trisamidoamine ligands of the type [(RNC₆H₄)₃N]^3- (L¹). When R is the electron-rich 4-<i>t</i>-Bu−Ph moiety, the ligand can undergo oxidative rearrangement and store oxidizing equivalents under specific conditions. Starting ferrous complexes of the general formula [(L¹)Fe^IIsolv]^- (solv = CH₃CN, dimethylformamide) can be easily oxidized (a) by dioxygen to afford the corresponding [(L¹)Fe^IIIOH]^- complexes, featuring several cases of terminal hydroxo units, and (b) by organochlorides (R−Cl) to provide [(L¹)Fe^IIIsolv] congeners and coupled R−R products. Efforts to synthesize [(L¹)Fe^III−O−Fe^III(L¹)]^2- by using [Cl₃Fe^III−O−Fe^IIICl₃]^2- indicate that intrinsic Fe^IIICl units can oxidatively rearrange the ligand to afford [(L¹_re)(Cl)Fe^II][Et₄N]₂, although the oxidizing equivalent is not retained. Compound [(L¹_re)(Cl)Fe^II][Et₄N]₂ can be further oxidized to [(L¹_re-2)(Cl)Fe^III][Et₄N] by CH₂Cl₂. Finally, oxidation of [(L¹)Fe^IIIsolv] by FeCl₃ affords [(L¹_reH)(Cl)Fe^II(<i>μ</i>-Cl)₂Fe^II(Cl)(L¹_re-2H)], which features a similar ligand rearrangement that also gives rise to a diamagnetic, doubly oxidized moiety. These results underscore the complexity of chemical transformations available to systems in which both the metal and the ligand are redox-active entities.