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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. Ruthenium Nitrosyl Porphyrins Coordinated with Aryloxides Containing Internal Hydrogen Bonds

   https://doi.org/10.1002/ejic.202400648  

   Warhausen, Adam_J; Zink, Jeremy_R; Ross, Bradley_J; Ramuglia, Anthony_R; Londoño‐Salazar, Jennifer; Shaw, Michael_J; Richter‐Addo, George_B (December 2024, European Journal of Inorganic Chemistry)

   Abstract The synthesis, characterization, and redox behavior of aryloxide complexes containing an increasing number of internal hydrogen bonds (OEP)Ru(NO)(OAr_xH) (OEP=octaethylporphyrinato dianion; x=0, 1, 2) are reported. These nitrosyl aryloxide compounds were characterized by X‐ray crystallography, IR and¹H NMR spectroscopy. The IR spectra displayed υ_NOfrequencies in the 1823–1843 cm⁻¹range with compounds possessing more internal hydrogen bonds demonstrating higher υ_NOfrequencies due to diminished π‐backdonation to the Ru−NO fragment. Comparison of the distinct υ_NHand δ_N−Hsignals in the IR and¹H NMR spectra of the free and complexed OAr_1H/OAr_2Hligands support the notion of additional electron density being removed via intramolecular hydrogen bonding. Results of DFT calculations on the (porphine)Ru(NO)(OAr_xH) models (porphine=unsubstituted porphyrin) reveal that the HOMOs of these complexes have significant axial ligand contributions, whereas the HOMOs of the five‐coordinate [(porphine)RuNO)]⁺cation resides mostly on the equatorial porphyrin macrocycle. The electrochemical results of these (OEP)Ru(NO)(OAr_xH) complexes in CH₂Cl₂reveal first oxidations that occur at increasingly positive potentials when more internal hydrogen bonds are present. Based on the DFT and preliminary IR spectroelectrochemical results, we propose that the electrooxidations result in eventual dissociation of the axial aryloxide ligands. 

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3. On the Preparation of Nickel Porphyrins Bearing Two to Four Nitro Groups at β ‐Positions

   https://doi.org/10.1002/ejoc.202500420  

   Tatar, Ameneh; Havlík, Martin; Navrátilová, Tereza; Uhlíková, Tereza; Drozdová, Michaela; Hricková, Karolína; Hajduch, Jan; Anzenbacher, Pavel; Dolenský, Bohumil (June 2025, European Journal of Organic Chemistry)

   The preparation, isolation, and identification of dinitro, trinitro, and tetranitro metalloporphyrins bearing nitro groups on pyrrole rings—desirable intermediates that enable fundamental changes in the chemico‐physical properties of the porphyrin core—are studied. All six possible dinitro‐Ni‐TPP isomers are formed; three are isolated as pure substances using column chromatography, while the remaining three are inseparable. All possible trinitro‐Ni‐TPP isomers are prepared and isolated, except for the 2,7,13 isomer. Attempts to synthesize tetranitro‐Ni‐TPP either through direct nitration of metalloporphyrin or via direct condensation of the nitropyrrole building blocks are unsuccessful. The molecular structures are unambiguously identified using 2D NMR experiments. Some experimental observations, though not all, are consistent with quantum chemical calculations performed on the geometry, energy, Fukui indices, dipole moments of nitroporphyrins, and the energy of nitration intermediates. 

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4. Structure, Properties, and Reactivity of Porphyrins on Surfaces and Nanostructures with Periodic DFT Calculations

   https://doi.org/10.3390/app10030740  

   Chilukuri, Bhaskar; Mazur, Ursula; Hipps, K. W. (February 2020, Applied Sciences)

   Porphyrins are fascinating molecules with applications spanning various scientific fields. In this review we present the use of periodic density functional theory (PDFT) calculations to study the structure, electronic properties, and reactivity of porphyrins on ordered two dimensional surfaces and in the formation of nanostructures. The focus of the review is to describe the application of PDFT calculations for bridging the gaps in experimental studies on porphyrin nanostructures and self-assembly on 2D surfaces. A survey of different DFT functionals used to study the porphyrin-based system as well as their advantages and disadvantages in studying these systems is presented. 

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5. The rigidity of self-assembled cofacial porphyrins influences selectivity and kinetics of oxygen reduction electrocatalysis

   https://doi.org/10.1039/D2DT02724K  

   Zhang, Daoyang; Crawley, Matthew R.; Fang, Ming; Kyle, Lea J.; Cook, Timothy R. (December 2022, Dalton Transactions)

   We report the electrocatalytic Oxygen Reduction Reaction on a rigid Co( ii ) porphyrin prism scaffold bridged by Ag( i ) ions. The reactivity of this scaffold differs significantly from previous prism catalysts in that its selectivity is similar to that of monomer (∼35% H 2 O) yet it displays sluggish kinetics, with an order of magnitude lower k s of ∼0.5 M −1 s −1 . The deleterious cofacial effect is not simply due to metal–metal separation, which is similar to our most selective prism catalysts. Instead we conclude the structural rigidity is responsible for these differences. 

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