Mn(III)-Porphyrin Immobilized on the Graphene Oxide-Magnetite Nanocomposite as an Efficient Heterogeneous Catalyst for the Epoxidation of Alkenes

Directly-Fused Ni(II)Porphyrin Conjugated Polymers with Blocked meso-Positions: Impact on Electrocatalytic Properties

The oxidative coupling reaction of two Ni(II) porphyrins meso-substituted with three and four phenyl groups, Ni(II) 5,10,15-(triphenyl)porphyrin (NiPh3P) and Ni(II) 5,10,15,20-(tetraphenyl)porphyrin (NiPh4P) respectively, was investigated in a oxidative chemical vapor deposition (oCVD) process. Irrespective of the number of meso-substituents, high-resolution mass spectrometry evidences the formation of oligomeric species containing up to five porphyrin units. UV-Vis-NIR and XPS analyses of the oCVD films highlighted a strong dependence of the intermolecular coupling reaction with the substrate temperature. Specifically, higher substrate temperatures yield lowering of valence band maxima and reduction of the band gap. The formation of conjugated polymeric assemblies results in increased conductivities as compared to their sublimed counterparts. Yet, electrocatalytic measurements exhibit water oxidation onset overpotentials (308 mV for pNiPh3P and 343 mV for pNiPh4P) comparatively higher than the onset overpotential measured for the oCVD film from Ni(II) 5,15-(diphenyl)porphyrin (pNiPh2P), i. e. 283 mV. Although DFT and comparative oCVD studies suggest the formation of directly fused porphyrins involving 'phenyl-mediated' and β-β linkages when reacting tetra-meso-substituted porphyrins, the present findings highlight that multiple direct fusion (β-β/meso-meso/β-β or meso-β/β-meso) is essential for Ni(II) porphyrin-based conjugated polymers to enable a dinuclear radical oxo-coupling operating mechanism for water oxidation at low overpotential and durable catalytic activity.

Biomimetic Chemical Reactions with Natural Products Using Metalloporphyrins and Salen Complexes as Catalysts: a Brief Review

The cytochrome P450 is a superfamily of hemoproteins mainly present in the liver and are versatile biocatalysts. They participate in the primary metabolism and biosynthesis of various secondary metabolites. Chemical catalysts are utilized to replicate the activities of enzymes. Metalloporphyrins and Salen complexes can contribute to the products' characterization and elucidate biotransformation processes, which are investigated during pre-clinical trials. These catalysts also help discover biologically active compounds and get better yields of products of industrial interest. This review aims to investigate which natural product classes are being investigated by biomimetic chemical models and the functionalities applied in the use of these catalysts. A limited number of studies were observed, with terpenes and alkaloids being the most investigated natural product classes. The research also revealed that Metalloporphyrins are still the most popular in the studies, and the identity and yield of the products obtained depend on the reaction system conditions.

Conjugated porphyrin polymer films with nickel single sites for the electrocatalytic oxygen evolution reaction

Directly fused nickel(ii) porphyrins are successfully investigated as heterogeneous single-site catalysts for the oxygen evolution reaction (OER). Conjugated polymer thin films from Ni(ii) 5,15-(di-4-methoxycarbonylphenyl)porphyrin (pNiDCOOMePP) and Ni(ii) 5,15-diphenylporphyrin (pNiDPP) showed an OER onset overpotential of 270 mV, and current densities of 1.6 mA cm^-2 and 1.2 mA cm^-2 at 1.6 V vs. RHE, respectively, representing almost a hundred times higher activity than those of monomeric thin films. The fused porphyrin thin films are more kinetically and thermodynamically active than their non-polymerized counterparts mainly due to the formation of conjugated structures enabling a dinuclear radical oxo-coupling (ROC) mechanism at low overpotential. More importantly, we have deciphered the role of the porphyrin substituent in the conformation and performance of porphyrin conjugated polymers as (1) to control the extension of the conjugated system during the oCVD reaction, allowing the retention of the valence band deep enough to provide a high thermodynamic water oxidation potential, (2) to provide a flexible molecular geometry to facilitate O₂ formation from the interaction between the Ni-O sites and to weaken the π-bond of the *Ni-O sites for enhanced radical character, and (3) to optimize the water interaction with the central metal cation of the porphyrin for superior electrocatalytic properties. These findings open the scope for molecular engineering and further integration of directly fused porphyrin-based conjugated polymers as efficient heterogeneous catalysts.