Journal of Porphyrins and Phthalocyanines

A stroll through memory lane highlighting the author's contributions to phthalocyanines, including synthetic aspects especially of binuclear species, manganese oxygen breathing chemistry, mixed valence species, solution and surface electrochemistry, electrocatalysis, two-electron concerted processes, charge transfer spectroscopy, ligand electrochemical parameter applications and phthalocyanine design.

Electronic absorption spectra of divalent metal (Ni(II) and Cu(II)) complexes of 2,3,7,8,12,13,17,18-octa(bromo/chloro)-5,10,15,20-tetraphenylporphyrins (MOXTPP; X = Br, Cl) were examined in various solvents. M(II) perhaloporphyrins exhibited dramatic shifts in their optical absorption spectral features relative to the corresponding metallotetraphenylporphyrins, MTPPs. Copper(II) perhaloporphyrins show significant red-shifts of the absorption bands in coordinating solvents relative to that observed for nickel(II) perhaloporphyrins. The large red-shift of the electronic absorption bands and the gain in intensity of the longest wavelength band (Q(0,0)), of Cu(II) perhaloporphyrins in certain coordinating solvents is comparable to that found in meso-tetraphenylporphinatozinc(II), ZnTPP. The solvent dependent spectral features of M(II) perhaloporphyrins are attributed to a coordinative interaction of the solvent with the core metal ion induced by the electron deficient porphyrin macrocycle.

The syntheses, characterizations and transformations of three tetraphenylporphyrins derived from methoxymethylated benzaldehyde 3 are described. Benzaldehyde 3 reacted with pyrrole under Lewis acid catalysis to give dipyrromethane 4 which was used as precursor in porphyrin syntheses. Porphyrins 6, αα-7 and αβ-7 were obtained using conditions for sterically encumbered benzaldehydes, with αα-7 and αβ-7 being atropisomers. The methoxymethyl groups of 6, αα-7 and αβ-7 were transformed into bromomethyl substituents (porphyrins 8, αα-9 and αβ-9) which were easily modified by nucleophilic reaction with the azide anion. Porphyrin azide 10 was subjected to a Staudinger phosphazene formation with triphenylphosphine. Subsequent reaction of the porphyrin phosphazene 12 with carboxylic acids gave acetamide 13, benzamide 14, and ferrocene carboxamide 15, respectively. Kornblum oxidation of monobromomethyl porphyrin 8 gave the formyl derivative 16.

Hybrid thin films of crystalline zinc oxide and the zinc complex of 5,10,15,20-tetrakis-(4-sulfonatophenyl)porphyrin (ZnTPPS) have been prepared by cathodic electrodeposition from different aqueous zinc salt solutions. Films from a solution containing zinc nitrate and the porphyrin derivate show a rough surface and porosity, whereas films prepared from an oxygen-saturated zinc chloride solution were very smooth. The presence of the porphyrin derivative in the deposition solution has a clear influence on the morphology of the hybrid films compared with pure zinc oxide films. In aqueous zinc nitrate solution the addition of the porphyrin derivative hinders the growth of zinc oxide. In contrast, the addition of the dye to the oxygen-saturated zinc chloride solution leads to an increase of the growth rate of ZnO/porphyrin hybrid films. An increased spectral absorbance was reached when two dyes (zinc complex of tetrasulfonated phthalocyanine and porphyrin) were added to the zinc nitrate solution since the electrodeposited hybrid thin films contained both dyes. UV-vis spectra revealed the presence of both macrocyclic metal complexes in the ZnO films.

The use of a high-field NMR instrument (ν(¹H) = 500 MHz) and 2-dimensional NMR techniques (HMQC, HMBC, ROESY) enabled us to fully assign the ¹H and ¹³C chemical shifts of bonellin dimethyl ester. The β-pyrrolic proton of C-3 appeared as a broad singlet at δ = 8.93, whereas that of C-8 gave a quartet with δ = 8.69 and ⁴J_H-H = |1.28| Hz. The C-2¹ methyl protons appeared as a doublet with δ = 3.55 and ⁴J_H-H = |1.07| Hz, while the C-7¹ methyl protons afforded a doublet with δ = 3.51 and ⁴J_H-H = |1.28| Hz. These results suggest that the β-pyrrolic carbons of ring A belong to the aromatic 18 π-electron [18]diazaannulene delocalization pathway, whereas those of ring B remain outside the aromatic pathway. The broadening of the C-3 β-pyrrolic proton signal can be attributed to the allylic 3-CH - 2¹-CH₃ coupling and the 3-CH - 21-NH coupling. At 330 K, the tautomeric exchange 21-NH_a ⇌ 23-NH_b is fast and only one broad signal at δ = -2.49 is seen for these protons. The ROESY spectrum showed clear correlation signals between the 18²-CH₃ and 17¹-CH₂ protons, the 18²-CH₃ and 17⁴-CH₃ protons, as well as between the 18¹-CH₃ and 17-CH protons. These results are compatible with the previous assignment that the absolute configuration at C-17 is S. Application of spin simulation enabled us to determine the chemical shifts and the ³J_H-H coupling constants of the 17-propionate side-chain. The ³J_H-H-values were used to calculate the populations for the 17¹-17 and 17²-17¹ rotamers. A relatively high population value of 0.41 was found for the 17¹-17 g^--rotamer, whose methoxycarbonylmethyl group points to the C-15 methine-bridge. This was interpreted as explaining the high tendency of bonellin to form anhydrobonellin. The rotational freedoms in the 13-propionate side-chain were studied by measuring the ¹H NMR spectra of the side-chain at temperatures between 300 and 195 K. At 300 K, the 13¹- and 13²-CH₂ proton signals appeared as deceptively simple triplets, which at 195 K were split into complex multiplets. At 195 K, the signal arising from the 13¹-CH₂ protons exhibited more splitting, which indicates that these protons have less rotational freedom than the 13²-CH₂ protons.

Compound 1 (2,4,6-tris(2-oxaphthalonitrile)-s-triazine) has been prepared by the reaction of 4-nitrophthalonitrile and cyanuric acid in dry DMF as the solvent in the presence of K₂CO₃ as the base. An interesting s-triazine, containing three oxa metal phthalocyanines (M = Zn, CoorCu) has been synthesized from compound 1, 4,5-bis(hexylthio)phthalonitrile and the corresponding anhydrous metal salts (Zn (OAc)₂, CoCl₂ or CuCl) by the method of statistically mixed condensation. The new compounds and phthalocyanines were obtained in sufficient purity after successive washings with different solvents and were characterized by elemental analysis, UV-vis, IR, NMR and EPR spectroscopy.

The reactivity of phthalonitrile, tetrafluorophthalonitrile and 4,5-dibutoxyphthalonitrile with unmodified surfaces of ZnO and SiO₂ and with the modified systems SiO₂/Cp₂Co, ZnO/Cp₂Co, SiO₂/Zn(AcAc)₂ prepared by deposition of cobaltocene (Cp₂Co) and zinc acetylacetonate Zn(AcAc)₂, was studied ("in-situ-synthesis") in processes of phthalocyanine coatings. The formation of structural uniform phthalocyanines on carriers were established by UV-vis and mass spectra. The compounds were used then to compare their catalytic and photocatalytic activities in the oxidation of sulfide as a test reaction.