Nucleophilic ring-opening of iron(III)-hydroxy-isoporphyrin

Zinc- and Cadmium meso-Aryl-Isoporphyrins: Non-Aromatic NIR Dyes with Distinct Conformational Features

A series of pyrrolyl and dipyrrinyl isoporphyrins carrying different phenyl and thienyl groups is reported. The compounds are obtained by a one-pot approach in the presence of a template reagent. Thienyl derivatives gave better yields, and were the only subclass to form with steric hindrance. The structural analyses carried out on compounds 1 and 14 revealed distinct conformational differences which are likely to result from an intramolecular NH… Cl hydrogen bridge of the pyrrolyl subclass. In addition, this hydrogen bridge strongly favors one of the two possible atropisomers. Hindered rotation of the meso-aryl groups is observed only in the cases of methylbenzothienyl derivatives 10 and 15 and leads to the observation of several diastereomers. NIR absorptions up to 923 nm are found throughout. Electrochemical investigations into the 1e- and 2e- reduced species unravel axial ligand exchange dynamics for the zinc isoporphyrin radical, and the probable formation of a zinc phlorinate.

Oxo-Free Hydrocarbon Oxidation by an Iron(III)-Isoporphyrin Complex

Metal-halides that perform proton coupled electron-transfer (PCET) oxidation are an important new class of high-valent oxidant. In investigating metal-dihalides, we reacted [Fe^III(Cl)(T(OMe)PP)] (1, T(OMe)PP = meso-tetra(4-methoxyphenyl)porphyrinyl) with (dichloroiodo)benzene. An Fe^III-meso-chloro-isoporphyrin complex [Fe^III(Cl)₂(T(OMe)PP-Cl)] (2) was obtained. 2 was characterized by electronic absorption, ¹H NMR, EPR, and X-ray absorption spectroscopies and mass spectrometry with support from computational analyses. 2 was reacted with a series of hydrocarbon substrates. The measured kinetic data exhibited a nonlinear behavior, whereby the oxidation followed a hydrogen-atom-transfer (HAT) PCET mechanism. The meso-chlorine atom was identified as the HAT agent. In one case, a halogenated product was identified by mass spectrometry. Our findings demonstrate that oxo-free hydrocarbon oxidation with heme systems is possible and show the potential for iron-dihalides in oxidative hydrocarbon halogenation.

Formation and Reactivity of New Isoporphyrins: Implications for Understanding the Tyr-His Cross-Link Cofactor Biogenesis in Cytochrome c Oxidase

Cytochrome c oxidase (CcO) catalyzes the reduction of dioxygen to water utilizing a heterobinuclear active site composed of a heme moiety and a mononuclear copper center coordinated to three histidine residues, one of which is covalently cross-linked to a tyrosine residue via a post-translational modification (PTM). Although this tyrosine-histidine moiety has functional and structural importance, the pathway behind this net oxidative C-N bond coupling is still unknown. A novel route employing an iron(III) meso-substituted isoporphyrin derivative, isoelectronic with Cmpd-I ((Por^•+)Fe^IV═O), is for the first time proposed to be a key intermediate in the Tyr-His cofactor biogenesis. Newly synthesized iron(III) meso-substituted isoporphyrins were prepared with azide, cyanide, and substituted imidazole functionalities, by adding nucleophiles to an iron(III) π-dication species formed via addition of trifluoroacetic acid to F₈Cmpd-I (F₈ = (tetrakis(2,6-difluorophenyl)porphyrinate)). Isoporphyrin derivatives were characterized at cryogenic temperatures via ESI-MS and UV-vis, ²H NMR, and EPR spectroscopies. Addition of 1,3,5-trimethoxybenzene or 4-methoxyphenol to the imidazole-substituted isoporphyrin led to formation of the organic product containing the imidazole coupled to aromatic substrate via a new C-N bond, as detected via cryo-ESI-MS. Experimental evidence for the formation of an imidazole-substituted isoporphyrin and its promising reactivity to form the imidazole-phenol coupled product yields viability to the herein proposed pathway behind the PTM (i.e., biogenesis) leading to the key covalent Tyr-His cross-link in CcO.

Calculations of current densities and aromatic pathways in cyclic porphyrin and isoporphyrin arrays

Magnetically induced current density susceptibilities have been studied for a number of cyclic ethyne- and butadiyne-bridged porphyrin and isoporphyrin arrays. The current density susceptibilities have been calculated using the gauge-including magnetically induced current (GIMIC) method, which is interfaced to the TURBOMOLE quantum chemistry code. Aromatic properties and current pathways have been analyzed and discussed by numerical integration of the current density susceptibilities passing selected chemical bonds yielding current strength susceptibilities. Despite the interrupted π-framework, zinc(ii) isoporphyrin sustains a ring current of ca. 10 nA T^-1. Porphyrin and isoporphyrin dimers sustain a significant current strength at the linker, whereas the larger porphyrinoid arrays sustain mainly local ring currents. Isoporphyrin dimers with saturated meso carbons have strong net diatropic ring-current strengths of 20 nA T^-1 fulfilling Hückels aromaticity rule. Porphyrin trimers and tetramers exhibit almost no current strength at the linker. The porphyrin moieties maintain their strong net diatropic ring current.

Magnesium porphyrins with relevance to chlorophylls

A review on the chemistry of magnesium porphyrins, which have significant interest owing to the relevance to chlorophyll molecules, is presented with emphasis on bicarbonate adducts of magnesium porphyrin and chlorophyll.