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(xpi(R))(3) (L-X(R); X = H, Br; R= cydohexyl (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 ((X)pi(R)) ((X)afa(R))(2)Fe (II) OH ((XLFeOH)-Fe-R-O-II), 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.