The Question of the Redox Site in Metal-Metal Multiple-Bonded Metallocorrole Dimers

We have revisited the electrochemistry of metallocorrole dimers with low-temperature cyclic voltammetry and UV–visible–NIR spectroelectrochemistry, with the aim of determining the sites of the redox processes undergone by these compounds. The systems studied include the metal–metal triple-bonded complexes {Ru[TpOMePC]}2 and {Os[TpOMePC]}2 and the metal–metal quadruple-bonded complex {Re[TPC]}2, where TpOMePC and TPC refer to trianionic meso-tris(p-methoxyphenyl)corrole and meso-triphenylcorrole ligands. For all three compounds, the first oxidation potentials are found at 0.52 ± 0.04 V vs SCE in CH2Cl2/0.1 M TBAP and are accompanied by major changes in the optical spectra, especially the appearance of broad, low-energy bands, suggesting macrocycle-centered oxidation in each case. In contrast, the reduction potentials span an 800 mV range, occurring at E1/2 = −0.52 V for {Re[TPC]}2, −0.81 V for {Ru[TpOMePC]}2, and −1.32 V for {Os[TpOMePC]}2, with more modest changes in the optical spectra, implying a significant metal-centered character in the reduction process. Density functional theory (DFT) calculations largely (but not entirely) bear out these expectations. The combined experimental and theoretical data indicate that one-electron addition to the Re dimer involves the Re–Re δ* LUMO, while one-electron addition to the Ru dimer largely involves the Ru–Ru π* LUMO. In contrast, the calculations suggest that one-electron reduction of the Os dimer occurs largely on the corrole ligands, a phenomenon attributed to the relativistic destabilization of the Os–Os π* MOs

β-nitro-5,10,15-tritolylcorroles

Functionalization of the β-pyrrolic positions of the corrole macrocycle with -NO 2 groups is limited at present to metallocorrolates due to the instability exhibited by corrole free bases under oxidizing conditions. A careful choice of the oxidant can limit the transformation of corroles into decomposition products or isocorrole species, preserving the corrole aromaticity, and thus allowing the insertion of nitro groups onto the corrole framework. Here we report results obtained by reacting 5,10,15-tritolylcorrole (TTCorrH 3) with the AgNO 2/ NaNO 2 system, to give mono- and dinitrocorrole derivatives when stoichiometry is carefully controlled. Reactions were found to be regioselective, affording the 3-NO 2TTCorrH 3 and 3,17-(NO 2) 2TTCorrH 3 isomers as the main products in the case of mono- and disubstitution, in 53 and 20% yields, respectively. In both cases, traces of other mono- and disubstituted isomers were detected, which were structurally characterized by X-ray crystallography. The influence of the β-nitro substituents on the corrole properties is studied in detail by UV-visible, electrochemical, and spectroelectrochemical characterization of these functionalized corroles. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations of the ground and excited state properties of these β-nitrocorrole derivatives also afforded significant information, closely matching the experimental observations. It is found that the β-NO 2 substituents conjugate with the π-aromatic system of the macrocycle, which initiates significant changes in both the spectroscopic and redox properties of the so functionalized corroles. This effect is more pronounced when the nitro group is introduced at the 2-position, because in this case the conjugation is, for steric reasons, more efficient than in the 3-nitro isomer. © 2012 American Chemical Society

Here’s looking at the reduction of noninnocent copper corroles via anion induced electron transfer

The synthesis, electrochemical and spectroscopic characterization of five copper triarylcorroles bearing one, two or three meso-nitroaryl substituents is reported. Redox potentials and spectroscopic properties of the neutral Cu(II) corrole cation radicals and singly reduced form of the complexes are reported in $\mathrm{CH}_{2}\mathrm{Cl}_{2}$ and the ability of the initial noninnocent derivatives to be chemically reduced via anion induced electron transfer (AIET) is explored using cyanide ($\mathrm{CN}^{-}$) or fluoride ($\mathrm{F}^{-}$) anions in the form of tetra-$n$-butylammonium salts. UV–visible spectra of the singly reduced corroles and the species generated after addition of $\mathrm{CN}^{-}$ or $\mathrm{F}^{-}$ to solutions of the neutral compounds are identical, thus confirming the AIET event in these systems. This result, when combined with the facile electrochemical reduction, provides strong indirect evidence for the presence of noninnocence in these systems

The Porphyrin Handbook

© 2003 Elsevier Science (USA). All rights reserved. The Porphyrin Handbook, Volume 11: Bioinorganic and Bioorganic Chemistry presents the fundamental aspects of the synthesis, structure, chemistry, and spectroscopy of phthalocyanines. This book discusses the biology and medical implications of porphyrin systems. Organized into seven chapters, this volume begins with an overview of the design, synthesis, and study of the structural and functional models of heme/copper terminal oxidases. This text then examines the proteins containing iron-protoporphyrin IX (heme), which play key roles in photosynthesis and respiration. Other chapters consider the syntheses of chiral porphyrin derivatives and summarize the uses of such compounds in enantioselective control. This book discusses as well the reactivity and synthesis of synthetic carbine metalloporphyrins. The final chapter deals with the B12-coenzymes, which is the most complex and physiologically important organometallic enzymatic reactions that directly depend on the reactivity of metal coordinated organic ligands. This book is a valuable resource for research scientists, clinicians, and engineers

The Porphyrin Handbook: Phthalocyanines: Synthesis

© 2003 Elsevier Science (USA). All rights reserved. The Porphyrin Handbook, Volume 15: Phthalocyanines: Synthesis provides information pertinent to every aspect of the chemistry, synthesis, spectroscopy, and structure of phthalocyanines. This book examines the biology and medical implications of porphyrin systems. Organized into five chapters, this volume begins with an overview of the importance of compounds such as heme and chlorophyll that play vital roles in the biological systems responsible for the transportation of oxygen to cells in the body. This text then explores the different methods used for the preparation of phthalocyanine and its metallated derivatives. Other chapters consider the detailed survey of phthalocyanine formation, characterization, and purification. This book discusses as well the synthesis of low-symmetry phthalocyanines and related compounds. The final chapter deals with a survey of the structure, synthesis, and physiochemical properties of porphyrazines with annulated heterocycles

The Porphyrin Handbook: The Iron and Cobalt Pigments: Biosynthesis, Structure and Degradation

© 2003 Elsevier Science (USA). All rights reserved. The Porphyrin Handbook, Volume 12: The Iron and Cobalt Pigments: Biosynthesis, Structure, and Degradation provides information pertinent to every aspect of the chemistry, synthesis, spectroscopy, and structure of phthalocyanines. This book presents the biochemical and clinical aspects of genetically transmitted or drug-induced diseases associated with errors in heme metabolism. Organized into eight chapters, this volume begins with an overview of the comparison of regulatory principles in animal and plant tetrapyrrole biosynthesis. This text then examines the biology and medical implications of porphyrin systems. Other chapters consider the transformation of hemes into bile pigments, the organic synthesis of bilins, and the pathways of degradation of chlorophyll in senescent plants. This book discusses as well the biosynthesis of porphyrins, vitamin B12, and chlorophylls. The final chapter deals with genome sequencing projects that provide sources of genes encoding the enzymes needed for the synthesis of the intermediates