Reactions of Grignard Reagents with Tin-Corrole Complexes: Demetalation Strategy and σ‑Methyl/Phenyl Complexes

An efficient, mild, and one-step methodology for the conversion of tin-corroles to the corresponding free base corroles has been developed. The Grignard reagent, namely, methylmagnesium chloride, is responsible for the facile demetalation of tin-corroles. In an optimized reaction, almost complete destannation is observed using methylmagnesium chloride in a representative corrolato-Sn­(IV)-chloride complex. This particular protocol has also been proven to be versatile on a wide variety of corrolato-Sn­(IV)-chloride substrates. Similar Grignard reagents, namely, methyl/phenylmagnesium bromides, however, failed to perform the desired demetalation reaction and rather resulted in the usual σ-methyl/phenyl complexes in good yields. In addition to two novel σ-phenyl complexes and three novel σ-methyl complexes, one new A₃-corrole and one new corrolato Sn­(IV)­chloride have also been synthesized. All the complexes have been thoroughly characterized by various spectroscopic techniques, including single-crystal X-ray structural analysis of the representative complexes. In the single-crystal X-ray data analyses, it was observed that the Sn–N and Sn–C bond distances are shorter than those in the similar tin porphyrin analogues. The ¹H NMR spectrum of a representative σ-methyl complex exhibits peaks corresponding to σ-bonded methyl groups in the high field regions at −3.39 ppm

NIR-emissive iridium(III) corrole complexes as efficient singlet oxygen sensitizers

Three new iridium(III) corrole complexes, having symmetrically and asymmetrically substituted corrole frameworks and judiciously varied axial ligands are prepared and characterized by various spectroscopic techniques including the X-ray structures of two of them. The observed phosphorescence at ambient temperature appears at much longer wavelengths than the previously reported Ir(III) porphyrin/corrole derivatives. Efficiencies of these compounds in the generation of singlet oxygen are also studied for the first time

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

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$^{IV}$, Cr$^V$, and Cr$^{VI}$ 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

Reactive Intermediates Involved in Cobalt Corrole Catalyzed Water Oxidation (and Oxygen Reduction)

A detailed investigation of the cobalt corrole Co­(tpfc) as molecular catalyst for electrochemical water oxidation uncovered many important mechanism-of-action details that are crucial for the design of optimally performing systems. This includes the identification of the redox states that do and do not participate in catalysis and very significant axial ligand effects on the activity of the doubly oxidized complex. Specifics deduced for the electrocatalysis under homogeneous conditions include the following: the one-electron oxidation of the cobalt­(III) corrole is completely unaffected by reaction conditions; catalysis coincides with the second oxidation event; two catalytic waves develop in the presence of OH^–, and the one at lower overpotential is dominant under more basic conditions. Comparative spectroelectrochemical measurements performed for Co­(tpfc) and Al­(tpfc), the analogous corrole chelated by the nonredox active aluminum, revealed that the second oxidation process of Co­(tpfc) is much more significantly metal-centered than the first one. EPR studies revealed that shift from fully corrole-centered to partially metal-centered in the singly oxidized complex [Co­(tpfc)]⁺ is achievable with fluoride as axial ligand. The analogous experiment, but with hydroxide instead of fluoride, could not be performed because of a surprising phenomenon: formation of a cobalt–superoxide complex that is actually relevant to oxygen reduction rather than to water oxidation. Nevertheless, fluoride and hydroxide induce very similar effects in terms of the appearance of two catalytic waves, lowering of onset potentials, and increasing the catalytic activity. The main conclusions from the accumulated data are that the apparent pH effect is actually due to hydroxide binding to the cobalt center and that π-donating axial ligands play pivotal and beneficial roles regarding the main factors that are important for facilitating the oxidation of water

Synthesis, Spectral Characterization, Structures, and Oxidation State Distributions in [(corrolato)Fe^III(NO)]^<i>n</i> (<i>n</i> = 0, +1, −1) Complexes

Two novel <i>trans</i>-A₂B-corroles and three [(corrolato)­{FeNO}⁶] complexes have been prepared and characterized by various spectroscopic techniques. In the native state, all these [(corrolato)­{FeNO}⁶] species are diamagnetic and display “normal” chemical shifts in the ¹H NMR spectra. For two of the structurally characterized [(corrolato)­{FeNO}⁶] derivatives, the Fe–N–O bond angles are 175.0(4)° and 171.70(3)° (DFT: 179.94°), respectively, and are designated as linear nitrosyls. The Fe–N (NO) bond distances are 1.656(4) Å and 1.650(3) Å (DFT: 1.597 Å), which point toward a significant Fe^III → NO back bonding. The NO bond lengths are 1.159(5) Å and 1.162(3) Å (DFT: 1.162 Å) and depict their elongated character. These structural data are typical for low-spin Fe­(III). Electrochemical measurements show the presence of a one-electron oxidation and a one-electron reduction process for all the complexes. The one-electron oxidized species of a representative [(corrolato)­{FeNO}⁶] complex exhibits ligand to ligand charge transfer (LLCT) transitions (cor­(π) → cor­(π*)) at 399 and 637 nm, and the one-electron reduced species shows metal to ligand charge transfer (MLCT) transition (Fe­(dπ) → cor­(π*)) in the UV region at 330 nm. The shift of the ν_NO stretching frequency of a representative [(corrolato)­{FeNO}⁶] complex on one-electron oxidation occurs from 1782 cm^–1 to 1820 cm^–1, which corresponds to 38 cm^–1, and on one-electron reduction occurs from 1782 cm^–1 to 1605 cm^–1, which corresponds to 177 cm^–1. The X-band electron paramagnetic resonance (EPR) spectrum of one-electron oxidation at 295 K in CH₂Cl₂/0.1 M Bu₄NPF₆ displays an isotropic signal centered at <i>g</i> = 2.005 with a peak-to-peak separation of about 15 G. The in situ generated one-electron reduced species in CH₂Cl₂/0.1 M Bu₄NPF₆ at 295 K shows an isotropic signal centered at <i>g</i> = 2.029. The 99% contribution of corrole to the HOMO of native species indicates that oxidation occurs from the corrole moiety. The results of the electrochemical and spectroelectrochemical measurements and density functional theory calculations clearly display a preference of the {FeNO}⁶ unit to get reduced during the reduction step and the corrolato unit to get oxidized during the anodic process. Comparisons are presented with the structural, electrochemical, and spectroelectrochemical data of related compounds reported in the literature, with a particular focus on the interpretation of the EPR spectrum of the one-electron oxidized form