Synthetic, Cyclic Voltammetric, Structural, EPR, and UV−Vis Spectroscopic Studies of Thienyl-Containing meso-A2B-cor(CrV═O) Systems: Consideration of Three Interrelated Molecular Detection Modalities

Ruffling and doming: Structural and redox studies on meso-aryl and β-alkyl chromyl(V)corroles

Chromyl(V) complexes of eleven different meso-aryl- and [Formula: see text]-alkylcorrole ligands have been prepared and characterized by analytical, spectroscopical, electrochemical and structural means. All seven new complexes show the expected optical spectra of chromyl(V) corroles with the Soret band situated slightly above (meso-arylcorroles) or below ([Formula: see text]-alkylcorrole) 400 nm, and with an isotropic room temperature EPR signal for the [Formula: see text] ion Cr(V) at about [Formula: see text]. Cyclic voltammetry evidences two or three quasi-reversible one-electron redox steps, which are characterized as two ligand-centered processes and one metal-centered process based on spectroelectrochemical measurements and a Hammett analysis. Chemical reduction to a chromyl(IV) corrolate was successfully performed using NaHg and NEt3. Citric acid, however, produces a different reduction product, for which an isocorrole structure is proposed. Six chromyl(V) corroles could be analysed by seven single crystal diffraction analyses. The obtained molecular data prove the presence of remarkably similar CrN4O coordination units independent of the corrole substitution pattern, and of macrocyclic conformations which can be understood as comprised mainly of a doming mode, a more or less pronounced saddling mode, and one out of two different and dominating ruffling modes.

Covalently Linked Bis(Amido-Corroles): Inter- and Intramolecular Hydrogen-Bond-Driven Supramolecular Assembly

Four bis-corroles linked by diamide bridges were synthesized through peptide-type coupling of a trans-A₂ B-corrole acid with aliphatic and aromatic diamines. In the solid state, the hydrogen-bond pattern in these bis-corroles is strongly affected by the type of solvent used in the crystallization process. Although intramolecular hydrogen bonds play a decisive role, they are supported by intermolecular hydrogen bonds and weak N-H⋅⋅⋅π interactions between molecules of toluene and the corrole cores. In an analogy to mono(amido-corroles), both in crystalline state and in solutions, the aliphatic or aromatic bridge is located directly above the corrole ring. When either ethylenediamine or 2,3-diaminonaphthalene are used as linkers, incorporation of polar solvents into the crystalline lattice causes a roughly parallel orientation of the corrole rings. At the same time, both NHCO⋅⋅⋅NH corrole hydrogen bonds are intramolecular. In contrast, solvation in toluene causes a distortion with one of the hydrogen bonds being intermolecular. Interestingly, intramolecular hydrogen bonds are always formed between the -NHCO- functionality located further from the benzene ring present at the position 10-meso. In solution, the hydrogen-bonds pattern of the bis(amido-corroles) is strongly affected by the type of the solvent. Compared with toluene (strongly high-field shifted signals), DMSO and pyridine disrupt self-assembly, whereas hexafluoroisopropanol strengthens intramolecular hydrogen bonds.

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.

Mn(V)(O) versus Cr(V)(O) Porphyrinoid Complexes: Structural Characterization and Implications for Basicity Controlling H-Atom Abstraction

Isomorphous crystals of Mn(V)(O) and Cr(V)(O) corrolazines were characterized by single crystal X-ray diffraction. Reactivity studies with H atom donors and separated PCET reagents show a dramatic difference in H atom abstracting abilities for these two complexes. The implied large difference in driving force is opposite the trend in redox potentials, indicating that basicity is a key factor in determining the striking difference in reactivity for two metal-oxo species in identical ligand environments.

A spectroscopic and theoretical investigation of a free-base meso-trithienylcorrole

The unique optical properties of free-base meso-tris(5-methylthien-2-yl)corrole were compared to those of the widely investigated meso-triphenyl-substituted analogue. A combination of spectroscopic and computational experiments was undertaken to elucidate the relationship between structural features of the neutral, mono-anionic and mono-cationic forms of the corroles and their corresponding optical properties. A general bathochromic shift was measured for the thienyl-substituted corrole. The experimental spectra are supported by excited state calculations. A systematic series of ground state minimizations were performed to determine energy minima for the flexible and solvent-sensitive molecules. Trithienylcorrole was found to have a more nonplanar macrocycle in conjunction with a high degree of π-overlap with the meso-substituents. Both structural features contribute to their bathochromically shifted optical spectra. The configurational character of the thienyl-substituted corrole is shown to have a larger degree of molecular orbital mixing and doubly excited character, which suggest a more complex electronic structure that does not fully adhere to the Gouterman four-orbital model. The reactivity of the thienyl groups, particularly with respect to their ability to be (electro)-polymerized, combined with the tight coupling of the meso-thienyl groups with the corrole chromophore elucidated in this work, recommends the meso-thienylcorroles as building blocks in, for instance, organic semiconductor devices.

Photochemical oxidation of a manganese(III) complex with oxygen and toluene derivatives to form a manganese(V)-oxo complex

Visible light photoirradiation of an oxygen-saturated benzonitrile solution of a manganese(III) corrolazine complex [(TBP8Cz)Mn(III)] (1): [TBP8Cz = octakis(p-tert-butylphenyl)corrolazinato(3-)] in the presence of toluene derivatives resulted in formation of the manganese(V)-oxo complex [(TBP8Cz)Mn(V)(O)]. The photochemical oxidation of (TBP8Cz)Mn(III) with O2 and hexamethylbenzene (HMB) led to the isosbestic conversion of 1 to (TBP8Cz)Mn(V)(O), accompanied by the selective oxidation of HMB to pentamethylbenzyl alcohol (87%). The formation rate of (TBP8Cz)Mn(V)(O) increased with methyl group substitution, from toluene, p-xylene, mesitylene, durene, pentamethylbenzene, up to hexamethylbenzene. Deuterium kinetic isotope effects (KIEs) were observed for toluene (KIE = 5.4) and mesitylene (KIE = 5.3). Femtosecond laser flash photolysis of (TBP8Cz)Mn(III) revealed the formation of a tripquintet excited state, which was rapidly converted to a tripseptet excited state. The tripseptet excited state was shown to be the key, activated state that reacts with O2 via a diffusion-limited rate constant. The data allow for a mechanism to be proposed in which the tripseptet excited state reacts with O2 to give the putative (TBP8Cz)Mn(IV)(O2(•-)), which then abstracts a hydrogen atom from the toluene derivatives in the rate-determining step. The mechanism of hydrogen abstraction is discussed by comparison of the reactivity with the hydrogen abstraction from the same toluene derivatives by cumylperoxyl radical. Taken together, the data suggest a new catalytic method is accessible for the selective oxidation of C-H bonds with O2 and light, and the first evidence for catalytic oxidation of C-H bonds was obtained with 10-methyl-9,10-dihydroacridine as a substrate.

Valence tautomerism in a high-valent manganese-oxo porphyrinoid complex induced by a Lewis acid

Addition of the Lewis acid Zn(2+) to (TBP(8)Cz)Mn(V)(O) induces valence tautomerization, resulting in the formation of [(TBP(8)Cz(+•))Mn(IV)(O)-Zn(2+)]. This new species was characterized by UV-vis, EPR, the Evans method, and (1)H NMR and supported by DFT calculations. Removal of Zn(2+) quantitatively restores the starting material. Electron-transfer and hydrogen-atom-transfer reactions are strongly influenced by the presence of Zn(2+).

Generation of an isolable, monomeric manganese(V)-oxo complex from O2 and visible light

The direct conversion of a Mn(III) complex [(TBP(8)Cz)Mn(III) (1)] to a Mn(V)-oxo complex [(TBP(8)Cz)Mn(V)(O) (2)] with O(2) and visible light is reported. Complex 1 is also shown to function as an active photocatalyst for the oxidation of PPh(3) to OPPh(3). Mechanistic studies indicate that the photogeneration of 2 does not involve singlet oxygen but rather likely occurs via a free-radical mechanism upon photoactivation of 1.

5d early-transition-metal corroles: a trioxo-bridged binuclear tungsten(VI) derivative

The synthesis and full characterization of the first tungsten corrole reveal that it is a binuclear trioxo-bridged complex of tungsten(VI), a coordination motif without precedence for tungsten chelated by other ligands.