Journal of Porphyrins and Phthalocyanines

The UV-visible spectrum of free-base octaethylcorrole, (OECor)H₃, was recorded in thirteen different nonaqueous solvents as well as in a mixed acetonitrile/acid solvent containing one of seven different acids. Spectra were also measured in seven different solutions of neat concentrated acid and in CH₃CN containing piperidine or tetrabutylammonium hydroxide as an added base. The overall data was analyzed as a function of solvent acidity or basicity parameters and the number of protons on the central nitrogens of the macrocycle, the predominant form of the corrole in these solutions being respresented as (OECor)H₃, [(OECor)H₄]⁺, [(OECor)H₂]⁻ or [(OECor)H]²⁻ where OECor = trianion of octaethylcorrole. The mono-protonated corrole, [(OECor)H₄]⁺, is formed in concentrated acetic acid or in CH₃CN containing 0.10 M trifluoroacetic acid, H₂SO₄, HCl, H₃PO₄ or HClO₄. The mono-deprotonated corrole, [(OECor)H₂]⁻, is generated in piperidine while doubly deprotonated [(OECor)H]²⁻ exists in solutions of tetrabutylammonium hydroxide. An addition of protons to the macrocycle of [(OECor)H₄]⁺ also occurs in the presence of concentrated strong acids and this results in a loss of the characteristic Soret band of the corrole leading presumably to [(OECor)H₅]²⁺ where the second proton has been added to a meso-position of the macrocycle. The UV-visible spectral changes upon formation of [(OECor)H₄]⁺, [(OECor)H₂]⁻ or [(OECor)H]²⁻ in CH₃CN were monitored during a titration with the relevent acid or base and equilibrium constants for protonation or deprotonation of (OECor)H3 were determined using standard equations. The measured logK values are compared to protonation and deprotonation constants obtained for two related corroles and two related porphyrins under the same experimental conditions.

As ²¹³Bi, a spontaneous alpha-emitting radioisotope, and ¹⁰B, a neutron-activated source of alpha particles, have been found to be potential tools in the treatment of cancer patients, a novel bismuth porphyrin, bearing both boron atoms and a strap with a hanging carboxylic group, was synthesized.

Different strategies for the demetalation of corrole complexes have been developed, using copper complexes of corrole as model compounds. Best results were obtained using the acidic mixture CHCl₃/H₂SO₄, which allowed the almost complete removal of copper ions from both meso-triaryl-, β-octaalkyl- and fully substituted corroles. This route reduced both the decomposition of the starting complex and the formation of isocorrole species produced by oxidation of the corrole ring in the acidic conditions necessary for the demetalation reaction. To investigate the scope of the reaction, the same approach was later extended to other metal complexes of corrole, such as cobalt, manganese, iron and germanium derivatives. Although not always successful, this approach demonstrated that in the case of corrole it is also possible to obtain a reversible coordination of metal ions, a route of synthetic interest for further functionalization of the corrole ring.

A systematic study on the effect of a catalyst on the aerobic oxidation of cyclohexane was carried out using cobalt isooctanoate, metalloporphyrin p-ClTPPCo and [p-ClTPPFe]₂O as catalysts. The results showed that the metalloporphyrin-catalyzed system performed better than the traditional cobalt salt (Co isooctanoate) in terms of both the reaction conversion and the selectivity of cyclohexanol and cyclohexanone (KA oil). More importantly, we discovered that bisironporphyrin complex, which was traditionally considered to be either non-active or not-so-active for hydrocarbon oxidation, excelled at 155°C, achieving high selectivity for KA oil (80%) and good reaction conversion (13.8%). This result is in sharp contrast to earlier results by others. Meanwhile, the production of adipic acid was also increased and good selectivity of adipic acid among the by-products was also obtained. Our study suggested that [p-ClTPPFe]₂O catalyzed aerobic oxidation could be used to produce adipic acid in addition to KA oil. Some mechanistic rationales were proposed to explain the superior performance of the [p-ClTPPFe]₂O catalyst based on its unique structural and chemical properties.

A series of carbene ruthenium-porphyrins [Ru(por)(:CR¹R²)] (por = TPP; R¹ = R² = p-C₆H₄Cl 2, p-C₆H₄Me 3, p-C₆H₄Ph 4; R¹ = Ph, R² = p-C₆H₄Ph 6; R¹ = Ph, R² = COPh 7; R¹ = p-C₆H₄Me, R² = CO(p-C₆H₄Me) 8; R¹ = COMe, R² = COPh 9; por = TTP; R¹ = R² = Ph 1', COPh 5') were synthesized and characterized. The starting material [Ru(por)(CO)] was treated with corresponding diazo compounds N₂CR¹R² in CH₂Cl₂ or octane for the diaryl carbene complexes 1', 2-4 and 6, while it was subjected to photolysis in THF, followed by reflux with the diazo compounds for the acyl carbene complexes 5' and 7-9. The compounds were robust in octane under reflux and were able to catalyze cyclopropanation reactions with methyl diazoacetate (MDA) toward a wide variety of alkenes. Monocyclopropanation of 25 alkenes was demonstrated with catalyst 3 in octane under reflux. By reaction with more than equimolar amounts of MDA in the presence of catalyst 9, the first porphyrin-catalyzed biscyclopropanation was attained toward nonconjugated α, ω-dienes, viz. 1,5-hexadiene and 1,7-octadiene.

Sulfonated metallophthalocyanines (PcS) are second generation photosensitizers for photodynamic therapy (PDT) of cancer. Metal-free H₂PcS are readily labeled with ⁶⁴Cu⁺⁺ to yield a mixture of sulfonated [⁶⁴Cu]CuPcS suitable for biodistribution studies in tumor-bearing rats by positron emission tomography (PET). Most of the ⁶⁴Cu activity was sequestrated within the kidneys (20%ID/g) and liver (12%ID/g) while tumor uptake values remained low (0.2%ID/g). Dissection and counting of individual tissue samples after the 24 h scan confirmed the uptake values derived from the PET images. The procedure can be applied to series of novel PcS to evaluate structure-tumor selectivity relationships as a parameter to select potential agents for photodynamic therapy.

A new class of 2,3,7,8-tetrabromo-5,10,15,20-tetrakis(4'-n-1-alkyloxyphenyl)porphyrins, H₂T(4'-OC_nP)PBr₄ (n = 4,6,8,10,12,14,16 and 18) and their Cu(II) complexes have been synthesized regioselectively and their mesophase properties explored. The mesogenic properties of the porphyrins were examined by differential scanning calorimetry and optical microscopy. An increase in alkyl chain length of the mesogens, showed an increase in melting point temperature and lowering of their clearing point temperatures with the narrower mesophases. This has been ascribed to the decreased π-π interactions as evidenced from the crystal structure of H₂T(4'-OC₆P)PBr₄·THF derivative. MT(4'-OC_nP)PBr₄ derivatives showed rectangular mesophases in contrast to discotic lamellar mesophases reported for the planar MT(4'-OC_nP)P mesogens.

Sublimed layers of Fe^IIMPyTPP and Fe^IIMPyTTP (MPyTPP and MPyTTP are meso-mono-4-pyridyl-triphenyl- and meso-mono-4-pyridyl-tri-p-tolyl-porphyrin dianions, respectively) consist of coordination oligomers that are formed by binding of pyridyl nitrogen atoms with the iron centers of the adjacent molecules in the film. Fourier transform infrared (FT-IR) spectroscopy including experiments with the ¹⁵NO₂ isotopomer demonstrates that the reaction of low pressure NO₂ gas with these layers leads to the formation of two types of complexes: six-coordinate nitro-complexes, in which the fifth site is occupied by the pyridyl group of the neighboring molecule in the layer and five-coordinate nitrito-complexes that terminate the oligomers. Further addition of NO₂ increments leads to the preferential oxidation of these nitrito ligands to bidentate nitrato ligands. These layers conserve their porosity upon standing and allow study of the oxo-transfer reactivity from coordinated nitro-groups to appropriate oxygen acceptors.