Chromium Complexes with Oxido and Corrolato Ligands: Metal‐Based Redox Processes versus Ligand Non‐Innocence

Abstract

Metal- versus ligand-centered redox processes and the effects of substituents on the ligands on the spectroscopic properties of the metal complexes are at the heart of research on metal complexes with non-innocent ligands. This work presents three examples of chromium complexes that contain both oxido and corrolato ligands, with the substituents on the corrolato ligands being different in the three cases. Combined X-ray crystallographic, electrochemical, UV/Vis/NIR/EPR spectroelectrochemical, and EXAFS/XANES measurements, together with DFT calculations, have been used to probe the complexes in three different redox forms. This combined approach makes it possible to address questions related to chromium- versus corrolato-centered redox processes, and the accessibility (or not) of Cr , Cr , and Cr in these complexes, as well as their spin states. To the best of our knowledge, these are the first EXAFS/XANES investigations on Cr-corrolato complexes in different redox forms, and hence these data should set benchmarks for future investigations on such complexes by this method.

Synthesis, Characterization, and the N Atom Transfer Reactivity of a Nitridochromium(V) Complex Stabilized by a Corrolato Ligand

“… 23 In the oxo[10-( p -hydroxyphenyl)-5,15-bis( m -bromophenyl)corrolato]chromium(V) derivative, the chromium atom is axially displaced from the N4 corrole plane by 0.57 Å. 23 …”

“…This displacement is comparable to the other literaturereported oxo(corrolato)chromium(V) derivatives. 23 In the oxo[10-(p-hydroxyphenyl)-5,15-bis(m-bromophenyl)corrolato]chromium(V) derivative, the chromium atom is axially displaced from the N4 corrole plane by 0.57 Å. 23 The chromium−nitrogen (pyrrolic) bond lengths are in the range of 1.988−1.997 Å.…”

“…Corroles are trianionic when fully deprotonated as opposed to porphyrin, which is dianionic . The inner π system of corrole is more electron-rich, and thus, it stabilizes the higher oxidation states of metals. − Transition metal complexes bearing multiple bonds between metals and ligands, e.g., nitrido, imido, oxo, alkylidyne, and alkylidene, have gained considerable research interest in recent times. − Multiple bonded metal–ligand complexes are frequently invoked in the atom and group transfer reactions. In this context, metal complexes bearing nitride ligands (MN) are at the forefront of current scientific research due to their resemblance with the metal complexes involved in the nitrogen fixation reactions. , Nitride complexes are also efficiently used in the nitrogenation reactions of various organic compounds. , The nitride ligand is also known for the stabilization of higher oxidation states of metals.…”

Heavy-element–ligand covalence: ligand noninnocence in molybdenum and tungsten Viking-helmet Corroles

“…Interestingly, while CrO triarylcorroles generally do not exhibit skeletal bond length alternations, 48 an electron-rich CrO-triarylcorrole with a 10-p-hydroxyphenyl substituent does, emphasizing the subtlety of the matter. 49 To complement the above crystallographic findings, we carried out scalar-relativistic DFT calculations using the Zeroth Order Regular Approximation (ZORA) to the Dirac equation (as implemented in the ADF program system) and all-electron STO-TZ2P basis sets on four model systems - the optimized geometries showed that the alternations are smaller in magnitude than for Mo[TPC]Cl 2 , potentially indicating a lower degree of corrole •2− character in the W case.…”

Structure Effects of Metal Corroles on Energy-Related Small Molecule Activation Reactions

“…This substituent effect plays crucial roles in determining the stability and the redox property of metal corroles, which are both significant factors considered in the catalysis of small molecule activation reactions. Many articles have been published regarding the influence of meso -substituent on the electrochemical and spectral properties of metal corroles. − Notably, electron-withdrawing groups can decrease the electron density on the aromatic corrole macrocycle, and thus increase their tolerance of oxidative degradation.…”