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1. Singlet Oxygen Generation in Peripherally Modified Platinum and Palladium Porphyrins: Effect of Triplet Excited State Lifetimes and meso ‐Substituents on 1 O 2 Quantum Yields

   https://doi.org/10.1002/cplu.202200010  

   Subedi, Dili R. ; Reid, Ryan ; D'Souza, Patrick F. ; Nesterov, Vladimir N. ; D'Souza, Francis ( March 2022 , ChemPlusChem)

   A series ofmeso‐substituted with aromatic (=tolyl, pyrenyl, fluorenyl, naphthyl, and triphenylamine) substituents, platinum (Pt), and palladium (Pd) porphyrins have been synthesized and characterized by spectroscopic and single‐crystal X‐ray diffraction studies to probe structure‐reactivity aspects on the electrochemical redox potentials, and phosphorescence quantum yields and lifetimes. In the X‐ray structures, the aromaticmeso‐substituents were rotated to some extent from the planarity of the porphyrin ring to minimize steric hindrance. Both Pt and Pd porphyrins revealed higher electrochemical redox gaps as compared to their free‐base porphyrin analogs as a result of the harder oxidation and reduction processes. The ability of both Pt and Pd porphyrins to generate singlet oxygen was probed by monitoring the photoluminescence of¹O₂at 1270 nm. Higher quantum yields for both triplet sensitizers compared to their free‐base analogs were witnessed. Singlet oxygen quantum yields close to unity were possible to achieve in the case of Pt and Pd porphyrins bearing triphenylamine substituents at themeso‐position. The present study brings out the importance of differentmeso‐substituents on the triplet porphyrin sensitizers in governing singlet oxygen quantum yields; a key property of photosensitizers needed for photodynamic therapy, chemical synthesis, and other pertinent applications.

    

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2. Next‐Generation D 2 ‐Symmetric Chiral Porphyrins for Cobalt(II)‐Based Metalloradical Catalysis: Catalyst Engineering by Distal Bridging

   https://doi.org/10.1002/anie.201812379  

   Hu, Yang ; Lang, Kai ; Tao, Jingran ; Marshall, McKenzie K. ; Cheng, Qigan ; Cui, Xin ; Wojtas, Lukasz ; Zhang, X. Peter ( February 2019 , Angewandte Chemie International Edition)

   NovelD₂‐symmetric chiral amidoporphyrins with alkyl bridges across two chiral amide units on both sides of the porphyrin plane (designated “HuPhyrin”) have been effectively constructed in a modular fashion to permit variation of the bridge length. The Co^IIcomplexes of HuPhyrin, [Co(HuPhyrin)], represent new‐generation metalloradical catalysts where the metal‐centered d‐radical is situated inside a cavity‐like ligand with a more rigid chiral environment and enhanced hydrogen‐bonding capability. As demonstrated with cyclopropanation and aziridination as model reactions, the bridged [Co(HuPhyrin)] functions notably different from the open catalysts, exhibiting significant enhancement in both reactivity and stereoselectivity. Furthermore, the length of the distal alkyl bridge can have a remarkable influence on the catalytic properties.

    

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3. Next‐Generation D 2 ‐Symmetric Chiral Porphyrins for Cobalt(II)‐Based Metalloradical Catalysis: Catalyst Engineering by Distal Bridging

   https://doi.org/10.1002/ange.201812379  

   Hu, Yang ; Lang, Kai ; Tao, Jingran ; Marshall, McKenzie K. ; Cheng, Qigan ; Cui, Xin ; Wojtas, Lukasz ; Zhang, X. Peter ( February 2019 , Angewandte Chemie)

   NovelD₂‐symmetric chiral amidoporphyrins with alkyl bridges across two chiral amide units on both sides of the porphyrin plane (designated “HuPhyrin”) have been effectively constructed in a modular fashion to permit variation of the bridge length. The Co^IIcomplexes of HuPhyrin, [Co(HuPhyrin)], represent new‐generation metalloradical catalysts where the metal‐centered d‐radical is situated inside a cavity‐like ligand with a more rigid chiral environment and enhanced hydrogen‐bonding capability. As demonstrated with cyclopropanation and aziridination as model reactions, the bridged [Co(HuPhyrin)] functions notably different from the open catalysts, exhibiting significant enhancement in both reactivity and stereoselectivity. Furthermore, the length of the distal alkyl bridge can have a remarkable influence on the catalytic properties.

    

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4. Transient Absorption Spectra of Metal‐Free and Transition‐Metal 5,10,15,20‐Tetraferrocene Porphyrins: Influence of the Central Metal Ion, Solvent Polarity, and the Axial Ferrocene Ligand

   https://doi.org/10.1002/ejic.202101007  

   Schrage, Briana R. ; Ermilov, Eugeny ; Nemykin, Victor N. ( April 2022 , European Journal of Inorganic Chemistry)

   The transient absorption spectra of the series of diamagnetic H₂TFcP, ZnTFcP, PdTFcP, and FcInTFcP compounds (TFcP(2‐)=5,10,15,20‐tetraferroceneporphyrin dianion) were investigated in polar (DMF) and non‐polar (toluene) solvents using excitation at 650 nm. The formation and the deactivation of the charge‐separated (Fc⁺‐Porphyrin^−.) state were observed in all cases. The lifetime of the charge‐separated state is nearly constant for all compounds (∼20 ps) and independent of the nature of the central ion and solvent. The formation of the triplet state in all the complexes was not observed. The third, minor long‐lived (160–480 ps) component was observed in polar DMF solvent. This component was tentatively assigned to the porphyrin species that are weakly bound to the carbonyl oxygen in DMF. DFT and TDDFT calculations on the ground state, excited state, and triplet state of the target compounds were in agreement with the experimental data.

    

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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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