Tuning the Fe(II/III) Redox Potential in Nonheme Fe(II)–Hydroxo Complexes through Primary and Secondary Coordination Sphere Modifications

The derivatization of the imino-functionalized tris­(pyrrolylmethyl)­amine ligand framework, N­(XpiR)3 (XLR; X = H, Br; R = cyclohexyl (Cy), phenyl (Ph), 2,6- diisopropylphenyl (DIPP)), is reported. Modular ligand synthesis allows for facile modification of both the primary and secondary coordination sphere electronics. The iron­(II)–hydroxo complexes, N­(XpiR)­(XafaR)2Fe­(II)­OH (XLRFeIIOH), are synthesized to establish the impact of the ligand modifications on the complexes’ electronic properties, including their chemical and electrochemical oxidation. Cyclic voltammetry demonstrates that the Fe­(II/III) redox couple spans a 400 mV range across the series. The origin of the shifted potential is explained based on spectroscopic, structural, and theoretical analyses of the iron­(II) and iron­(III) compounds.