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1. Synthesis of 2-bromo- and 2-phenyl-neo-confused porphyrins

   https://doi.org/10.1039/d0ob01642j  

   Almejbel, Arwa S.; Lash, Timothy D. (September 2020, Organic & Biomolecular Chemistry)

   null (Ed.)

   Neo-confused porphyrins (neo-CPs), porphyrin isomers with a 1,3-connected pyrrolic subunit, are aromatic structures with a CNNN coordination core. Previously, examples of neo-CPs with fused benzo units or electron-withdrawing ester substituents have been described. In this paper, two new examples of neo-CPs are reported that lack a fused aromatic unit or an ester moiety, but instead have a bromo or phenyl substituent on the neo-confused ring. Acid-catalyzed condensation of suitably substituted 1,2′-dipyrrylmethane dialdehydes with a 2,2′-dipyrrylmethane, followed by oxidation with aqueous ferric chloride solutions, afforded the neo-CPs in 40–45% yield. These porphyrin analogues had slightly reduced diatropic ring currents and slowly decomposed in solution. The related palladium( ii ) and nickel( ii ) complexes proved to be very unstable, even though the diatropicity of the macrocycle was enhanced. This study shows that stabilizing substituents are necessary for investigations into this class of porphyrinoids. Attempts to prepare imidazole versions of neo-CPs were unsuccessful. 

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2. Alternative Metal with an Alternative Mechanism for Metalloporphyrin-Enabled NO Reduction to N ₂ O: A Combined Computational and Experimental Investigation of NO Reduction by Cr Porphyrin with Lewis Acid

   https://doi.org/10.1021/acs.inorgchem.5c00226  

   Baizhigitova, Dariya; Abucayon, Erwin G; Khade, Rahul L; Kapfunde, Tsitsi A; Richter-Addo, George B; Zhang, Yong (March 2025, Inorganic Chemistry)

   Nitric oxide (NO) is an important molecule that regulates many physiological processes in humans and plants and contributes to the formation of greenhouse gases. Bacterial NO reductases utilize a di-Fe heme/nonheme active site to couple two NOs to generate nitrous oxide (N2O) via a two-electron mechanism. Here, we report a previously unexplored Cr porphyrin NO complex with a Lewis acid (LA) BF3 for the NO reduction reaction. Density functional theory calculations were first employed to reveal its reaction mechanism with a reasonable barrier for experimental realization. Subsequent experimental synthesis work confirms this reactivity and reports the first nitrosyl Cr porphyrin X-ray crystal structure. Theoretical analysis uncovered a distinctive reaction feature for the Cr system compared to Fe and Co porphyrins: the electron transfer from the metal to the bound NO occurs before LA binding. A comparative study of the NO coupling mechanisms with the three representative metals suggests that the metal reduction potential should be finely tuned, as found in previous studies of NOR enzymatic systems. Overall, this study offers new theoretical and experimental insights to further facilitate the development of alternative NO reduction compounds with biological, environmental, and industrial applications. 

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3. A PEGylated Tin Porphyrin Complex for Electrocatalytic Proton Reduction: Mechanistic Insights into Main‐Group‐Element Catalysis

   https://doi.org/10.1002/anie.202206325  

   Chaturvedi, Ashwin; McCarver, Gavin A.; Sinha, Soumalya; Hix, Elijah G.; Vogiatzis, Konstantinos D.; Jiang, Jianbing (July 2022, Angewandte Chemie International Edition)

   Abstract Electrocatalytic proton reduction to form dihydrogen (H₂) is an effective way to store energy in the form of chemical bonds. In this study, we validate the applicability of a main‐group‐element‐based tin porphyrin complex as an effective molecular electrocatalyst for proton reduction. A PEGylated Sn porphyrin complex (SnPEGP) displayed high activity (−4.6 mA cm⁻²at −1.7 V vs. Fc/Fc⁺) and high selectivity (H₂Faradaic efficiency of 94 % at −1.7 V vs. Fc/Fc⁺) in acetonitrile (MeCN) with trifluoroacetic acid (TFA) as the proton source. The maximum turnover frequency (TOF_max) for H₂production was obtained as 1099 s⁻¹. Spectroelectrochemical analysis, in conjunction with quantum chemical calculations, suggest that proton reduction occurs via an electron‐chemical‐electron‐chemical (ECEC) pathway. This study reveals that the tin porphyrin catalyst serves as a novel platform for investigating molecular electrocatalytic reactions and provides new mechanistic insights into proton reduction. 

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4. Synthesis of a light-harvesting ruthenium porphyrin complex substituted with BODIPY units. Implications for visible light-promoted catalytic oxidations

   https://doi.org/10.1039/D1NJ00189B  

   Malone, Jonathan; Klaine, Seth; Alcantar, Christian; Bratcher, Fox; Zhang, Rui (March 2021, New Journal of Chemistry)

   null (Ed.)

   A light-harvesting ruthenium porphyrin substituted covalently with four boron–dipyrrin (BODIPY) moieties has been synthesized and studied. The resulting complex showed an efficient decarbonylation reaction predominantly due to a photo-induced energy transfer process. Chemical oxidation of the ruthenium( ii ) BODIPY–porphyrin afforded a high-energy trans -dioxoruthenium( vi ) species that is one order of magnitude more reactive towards alkene oxidation than those analogues supported by conventional porphyrins. In the presence of visible light, the ruthenium( ii ) BODIPY–porphyrin displayed remarkable catalytic activity toward sulfide oxidation and alkene epoxidation using iodobenzene diacetate [PhI(OAc) 2 ] and 2,6-dichloropyridine N -oxide (Cl 2 pyNO) as terminal oxidants, respectively. The findings in this work highlight that porphyrin–BODIPY conjugated metal complexes are potentially useful for visible light-promoted catalytic oxidations. 

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5. Electrocatalytic production of hydrogen peroxide enabled by post-synthetic modification of a self-assembled porphyrin cube

   https://doi.org/10.1039/d2qi02050e  

   Crawley, Matthew R.; Zhang, Daoyang; Cook, Timothy R. (December 2022, Inorganic Chemistry Frontiers)

   Self-assembled metallacyles and cages formed via coordination chemistry have been used as catalysts to enforce 4H + /4e − reduction of oxygen to water with an emphasis on attenuating the formation of hydrogen peroxide. That said, the kinetically favored 2H + /2e − reduction to H 2 O 2 is critically important to industry. In this work we report the synthesis, characterization, and electrochemical benchmarking of a hexa-porphyrin cube which catalyses the electrochemical reduction of molecular oxygen to hydrogen peroxide. An established sub-component self-assembly approach was used to synthesize the cubic free-base porphryin topologies from 2-pyridinecarboxaldehyde, tetra-4-aminophenylporphryin (TAPP), and Fe(OTf) 2 (OTf − = trifluoromethansulfonate). Then, a tandem metalation/transmetallation was used to introduce Co( ii ) into the porphyrin faces of the cube, and exchange with the Fe( ii ) cations at the vertices, furnishing a tetrakaideca cobalt cage. Electron paramagnetic resonance studies on a Cu( ii )/Fe( ii ) analogue probed radical interactions which inform on electronic structure. The efficacy and selectivity of the CoCo-cube as a catalyst for hydrogen peroxide generation was investigated using hydrodynamic voltammetry, revealing a higher selectivity than that of a mononuclear Co( ii ) porphyrin (83% versus ∼50%) with orders of magnitude enhancement in standard rate constant ( k s = 2.2 × 10 2 M −1 s −1 versus k s = 3 × 10 0 M −1 s −1 ). This work expands the use of coordination-driven self-assembly beyond ORR to water by exploiting post-synthetic modification and structural control that is associated with this synthetic method. 

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