The first examples for the facile, reversible, and stepwise electrogeneration of triply ring-reduced porphyrin macrocycles are presented. The investigated compounds are represented as MTPP(NO)(PE), MTTP(PE), NiTPP(NO)(Ph), and MTPP(CN), where TTP and TPP are the dianions of tetratolylporphyrin and tetraphenylporphyrin, respectively, NO, phenylethynyl (PE), and CN are substituents at the β-pyrrole positions of the macrocycle, and M = Cu, Ni, Zn, Co, or 2H. Each porphyrin undergoes three or four reductions within the negative potential limit of the electrochemical solvent. The UV-visible spectra of the first three reduction products were characterized by means of thin-layer UV-vis spectroelectrochemistry, and the generation of multianionic porphyrins is interpreted in terms of extensive stabilization of the LUMOs due to the electron-withdrawing and/or extended π-conjugation of the β-substituents.

Di- and octa-phenylethynyl (PE) substituted π-extended copper corroles were synthesized and characterized as to their structural, electrochemical and spectroscopic properties. The addition of two or eight PE groups to the β-pyrrole positions of the corrole results in dramatic red shifts in the electronic absorption spectra and new reductions which are not seen for the parent compound lacking PE substituents. CuCor(PE) is reduced in four reversible one-electron transfer steps to give derivatives of [CuCor(PE)] where n = 1, 2, 3 or 4. Variable temperature H NMR and EPR measurements were carried out and suggest that the octa- and di-PE substituted Cu-corroles can both be described as an antiferromagnetically coupled Cu corrole cation radical which is in equilibrium with a triplet state, possibly due to a lower singlet-triplet energy gap as compared to 1 and 2 at room temperature. The EPR spectra of one-electron oxidized and one electron reduced species exhibited the characteristics of Cu(ii) corroles. The products generated in the first two reductions of each π-extended corrole were characterized by thin-layer spectroelectrochemistry, thus providing new insights into how UV-vis spectra of highly reduced corroles vary as a function of the number of PE groups and overall charge on the molecule. The singly reduced and singly oxidized copper corroles were also chemically generated in CHCN and shown to have UV-visible spectra almost identical to the spectra obtained by electroreduction or electrooxidation in PhCN or THF containing 0.1 M tetrabutylammonium perchlorate.

Corroles, macrocycles that owe their name to the cobalt‐chelating prosthetic group of vitamin B12 and share numerous features with the iron‐chelating porphyrin present in heme proteins/enzymes, constantly cross new boundaries ever since stable derivatives became easily accessible. Particularly important is the increasing utilization of corroles and the corresponding metal complexes for the benefit of mankind, in terms of new drug candidates for treating various diseases and as catalysts for sustainable energy relevant processes. One challenge is to gain access to the plain macrocycle, as to allow for full elucidation of the most fundamental properties of corroles. We have obtained the substituent‐free corrole by several surprising and conceptually different pathways. Selected features of the corresponding metal complexes are illuminated, for pointing towards unique phenomena that are anticipated to largely expand the horizon regarding their utilization for contemporary catalysis.

Summary Stable complexes with terminal triply bound metal-oxygen bonds are usually not considered as valuable catalysts for the hydrogen evolution reaction (HER). We now report the preparation of three conceptually different (oxo)molybdenum(V) corroles for testing if proton-assisted 2-electron reduction will lead to hyper-reactive molybdenum(III) capable of converting protons to hydrogen gas. The upto 670 mV differences in the [(oxo)Mo(IV)] - /[(oxo)Mo(III)] −2 redox potentials of the dissolved complexes came into effect by the catalytic onset potential for proton reduction thereby, significantly earlier than their reduction process in the absence of acids, but the two more promising complexes were not stable at practical conditions. Under heterogeneous conditions, the smallest and most electron-withdrawing catalyst did excel by all relevant criteria, including a 97% Faradaic efficiency for catalyzing HER from acidic water. This suggests complexes based on molybdenum, the only sustainable heavy transition metal, as catalysts for other yet unexplored green-energy-relevant processes.

Tris- and tetrakis-β-trifluoromethylated gallium (3CF3-Ga, 4CF3-Ga) and aluminum (3CF3-Al, 4CF3-Al) corrole systems were synthesized by a facile “one-pot” approach and studied in the context of photocatalytic C–H bond activation.

Synthesis of 5,10,15-tris(trifluoromethyl)corrole Procedure A, with isolation of the bilane The oligomerization step: Sodium dithionite (3 g,15 mmol) and sodium hydrogen carbonate (3.5 g, 42 mmol) were suspended in aqueous acetonitrile solution (H2O:acetonitrile, 1:2, v/v, 30 mL) in a 250 mL three-necked flask placed in a preheated oil bath (45°C-50°C) fitted with a magnetic bar, thermometer, rubber septum and a reflux condenser connected to an oil bubbler. After increasing the bath temperature to 70°-80° C, a mixture of pyrrole (2.77 mL, 40 mmol) and halothane (3.20 mL, 30 mmol) was injected with a syringe through the septum. Noticeable gas evolution (CO2) occurred, as the yellow suspension was continually stirred and maintained at 70°-80° for 2h. Progress of the reaction was monitored by HPLC analysis. By the end of the reaction almost all inorganic salts were dissolved. After cooling to room temperature, water (50 mL) was added and the reaction mixture was extracted with diethyl ether (3×30 mL). The organic layer was washed with water and then dried over anhydrous Na2SO4. Gentle removal of the solvent on a rotary evaporator provided the oily crude mixture that was separated (silica gel column chromatography) by gradually increasing the amount of DCM (0-100%) in hexane. All the fractions were collected using Erlenmeyer flasks (50 mL) and small amounts from each were added to a test tube for reaction with DDQ, as only fractions containing the bilane become fluorescent upon that treatment. Dipyrromethane 1 was collected from 0-30% DCM/hexane fractions, tripyrromethane from the 30-90% DCM/hexane fractions and tetrapyrrane (bilane) from the 90-100% fractions. Pentapyrrane (a precursor of sapphyrin) was eluted the latest. All products except tripyrrane are liquids. The total amount of isolated tetrapyrrane was 1.5 g, 3 mmol (30% yield). General reaction conditions for oxidation by PIFA: Bilane (0.5 g, 0.9 mmol) was dissolved in DCM or acetonitrile or propionitrile (200 mL) and purged with Ar gas for 20 min. Then PIFA (1 g, 2.3 mmol) was

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Heme-like metal-chelating macrocycles, including expanded and contracted porphyrins, are of everlasting interest as drug candidates for numerous diseases. Still, all reported corrole derivatives (and most other heme analogues) do not fulfill the most basic standards expected for oral drug administration: a combination of low molecular weight and reasonable water solubility. We now disclose a very straightforward synthetic method that relies on surprisingly facile trifluoromethyl hydrolysis for gaining access to a new class of corroles that do satisfy all druglikeness criteria. The relevance is briefly exemplified for the iron corroles by demonstrating the ability to affect their association with plasma proteins and their performance for catalase-like decomposition of hydrogen peroxide.