Porphyrazines with annulated diazepine rings. 3.⊗ MgII Complex of 4-tert-Butylphenyl Substituted Tetra(1,4-diazepino)porphyrazine: Synthesis and Peculiar Effect of Solvent on Its Spectral Properties

5,7-Di(4-tert-butylphenyl)-6H-1,4-diazepine-2,3-dicarbonitrile, prepared by condensation of di(4-tert-butylbenzoyl) methane with diaminomaleodinitrile, affords upon template cyclotetramerization in the presence of magnesium(II) butoxide in n-butanol the MgII complex of octa-4-tert-butylphenyl substituted tetra(1,4-diazepino)porphyrazine. The strong solvent effect on its UV-Vis and 1H NMR spectral properties is rationalized in terms of dimerization occurring very likely due to intermolecular hydrogen bonding between diazepine nitrogen atoms and water molecules. The monomer is present exclusively only in diluted solutions of aprotic solvents such as dimethyl sulfoxide and dimethylformamide. Addition of water or methanol leads to dimerization. The dimer exists also in pyridine and tetrahydrofuran solutions, as well in benzene and dichloromethane containing residual water or alcohol. The UV-Vis spectrum of the monomer is typical for MgII porphyrazines and contains a single Q band at ca. 680 nm. In its 1H NMR spectrum the resonance of the CH2 protons is not observed at ambient temperatures but appear as a broad signal at 4.4-4.5 ppm above 100 °C, which is characteristic for rapid inversion of the 1,4-diazepine ring in the 6H form. The Q band of the dimer is split into two components (major at 640-645 nm and minor at 680-685 nm). The dimer gives two doublets of the diastereotopic CH2 protons (5.9-7.1 ppm for the equatorial and 4.8-6.1 ppm for the axial CH2 protons, depending on the solvent) with characteristic geminal splitting of ca. 11-12 Hz. Formation of the dimer hinders the inversion of diazepine rings and two sharp doublets are observed even above 100 °C. © ISUCT Publishing

Porphyrazines with annulated diazepine rings. 4. Synthesis and properties of Mg-II tetradiazepinoporphyrazine carrying exocyclic styryl fragments

A novel tetradiazepinoporphyrazine MgII complex bearing eight peripheral styryl substituents, [St(8)TDzPAMg(H2O)] (St = -CH=CHAr, where Ar = 4-methoxyphenyl) was prepared by template cyclotetramerization of the corresponding precursor - 5,7-distyryl substituted diazepino-2,3- dicarbonitrile - in the presence of Mg-II butoxide in n-butanol. UV-visible and H-1 NMR spectral data indicate that the complex is strongly aggregated in non-coordinating solvents (dichloromethane, chloroform, benzene), it is dimeric in pyridine, whereas it is predominantly monomeric in dimethylsulfoxide and dimethylformamide. The fluorescence response is high for solutions in which the monomeric form is prevalent, but it is strongly quenched as the content of the dimer is increased. Evidence was obtained that dimerization occurs due to intermolecular hydrogen bonding between acidic CH2 groups in the diazepine ring (6H form) of one molecule with meso- and/or diazepine N atoms of another molecule, dimerization being also contributed by the presence of chlatrated water. In the presence of fluoride anions the dimer is destroyed with formation of the monomeric species, which is changed to the 1H form upon heating, as indicated by H-1 NMR spectra

Iron phthalocyanine derived Fe1/h-BN single atom catalysts for CO2 hydrogenation

Iron phthalocyanine-coated hexagonal boron nitride (FePc/h-BN) nanoparticles, obtained by FePcCl adsorption on the h-BN surface from a dimethylformamide solution, were subjected to heat treatment in order to form single atom Fe1/h-BN catalysts. Samples were characterized by means of X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, scanning and transmission electron microscopy, and temperature-programmed oxidation/reduction/desorption. The FePc deposition process was optimized to avoid the formation of nanoparticles. FePc exhibits high thermal stability in a hydrogen atmosphere and decomposes into a single iron atom when oxidizing in an O2 flow at 350 °C (sample Fe1-ox/h-BN). Subsequent reductive heat treatment in hydrogen (sample Fe1-red/h-BN) results in the formation of Fe-based nanoparticles due to Fe1 diffusion and association, resulting in a decrease in catalytic activity. Hydrogenation proceeds according to the Eley-Rideal mechanism with CO2 chemisorption on the Fe1 surface species (Fe1-ox/h-BN) and is changed to the Langmuir-Hinshelwood mechanism (Fe1-red/h-BN). Selectivity for hydrocarbons increases after reduction of the Fe1-ox/h-BN sample. Our results open up new possibilities for using metal phthalocyanine as a precursor for cheap, reproducible, and efficient single atom catalysts for CO2 hydrogenation.</p