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)(3)N](3-) (L-1). When R is the electron-rich 4-t-Bu-Ph moiety, the ligand can undergo oxidative rearrangement and store oxidizing equivalents under specific conditions. Starting ferrous complexes of the general formula [(L-1)Fe(II)solv](-) (solv = CH3CN, dimethylformamide) can be easily oxidized (a) by dioxygen to afford the corresponding [(L-1)(FeOH)-O-III](-) complexes, featuring several cases of terminal hydroxo units, and (b) by organochlorides (R-Cl) to provide [(L-1)Fe(III)solv] congeners and coupled R-R products. Efforts to synthesize [(L-re(1))Fe-III-O-Fe-III(L-1)](2-) by using [Cl3FeIII-O-(FeCl3)-Cl-III](2-) indicate that intrinsic (FeCl)-Cl-III units can oxidatively rearrange the ligand to afford [(L-re(1))(Cl)Fe-II][Et4N](2), although the oxidizing equivalent is not retained. Compound [(L-re(1)) (Cl) Fe-II][Et4N](2) can be further oxidized to [(L-re-2(1))(Cl)Fe-III][Et4N] by CH2Cl2. Finally, oxidation of [(L-1)Fe(III)solv] by FeCl3 affords [((LreH)-H-1)(Cl)Fe-II(mu-Cl)(2)Fe-II(Cl)((Lre-2H)-H-1)], 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.