Ligand Noninnocence in Iron Corroles: Insights from Optical and X-ray Absorption Spectroscopies and Electrochemical Redox Potentials

Abstract

<p class="first" id="P1">Two new series of iron <i>meso</i>-tris( <i>para</i>-X-phenyl)-corrole (T <i>p</i>XPC) complexes, Fe[T <i>p</i>XPC]Ph and Fe[T <i>p</i>XPC]Tol, in which X=CF ₃, H, Me, and OMe, and Tol= <i>p</i>-methylphenyl ( <i>p</i>-tolyl), have been synthesized, allowing a multitechnique electronic–structural comparison with the corresponding FeCl, FeNO, and Fe ₂( <i>μ</i>-O) T <i>p</i>XPC derivatives. Optical spectroscopy revealed that the Soret maxima of the FePh and FeTol series are insensitive to the phenyl <i>para</i> substituent, consistent with the presumed innocence of the corrole ligand in these compounds. Accordingly, we may be increasingly confident in the ability of the substituent effect criterion to serve as a probe of corrole noninnocence. Furthermore, four complexes—Fe[TPC]Cl, Fe[TPC](NO), {Fe[TPC]} ₂O, and Fe[TPC]Ph—were selected for a detailed XANES investigation of the question of ligand noninnocence. The intensity-weighted average energy (IWAE) positions were found to exhibit rather modest variations (0.8 eV over the series of corroles). The integrated Fe-K pre-edge intensities, on the other hand, vary considerably, with a 2.5 fold increase for Fe[TPC]Ph relative to Fe[TPC]Cl and Fe[TPC](NO). Given the approximately <i>C</i> ₄ <i> _v </i> local symmetry of the Fe in all the complexes, the large increase in intensity for Fe[TPC]Ph may be attributed to a higher number of 3d holes, consistent with an expected Fe ^IV-like description, in contrast to Fe[TPC]Cl and Fe[TPC](NO), in which the Fe is thought to be Fe ^III-like. These results afford strong validation of XANES as a probe of ligand noninnocence in metallocorroles. Electrochemical redox potentials, on the other hand, were found not to afford a simple probe of ligand noninnocence in Fe corroles. </p><p id="P2">Like optical spectroscopy, X-ray absorption near-edge spectroscopy (XANES) provides an excellent probe of ligand noninnocence in iron corroles. Electrochemical redox potentials, on the other hand, do not correlate straightforwardly with ligand noninnocence. </p><p id="P3"> <div class="figure-container so-text-align-c"> <img alt="" class="figure" src="/document_file/08be93e9-fb1c-4875-814f-97233fc259d2/PubMedCentral/image/nihms921586u1.jpg"/> </div> </p>