Journal of Porphyrins and Phthalocyanines

The discovery and characterization of the first example of a bis-cadmiumtris-phthalocyanine triple-decker sandwich complex is reviewed. The compound, with each Pc ring substituted at the eight non-peripheral positions with hexyl chains, was obtained unexpectedly during recrystallization of the corresponding monomeric 1,4,8,11,15,18,22,25-octa-hexyl cadmium phthalocyanine from CH₂Cl₂ and methanol. The scope for obtaining further examples of this new class of complex bearing different ring substituents is also described. A feature of the compounds is that they give an EPR signal. An electrochemical study has shown that the rest state of the core of the sandwich structure is a dianion arising from the imbalance of the charges on the two cadmium atoms and the three Pc^2- ligands. This is a spin 0 species. It is proposed that the free radical character arises because the potential for the first one-electron oxidation is unusually low for a phthalocyanine, allowing for the partial presence of the spin ½ species for non-peripherally substituted complexes and a more extensive presence of the EPR active redox state for peripherally substituted analogs. Results of chemical oxidation using iodine are also discussed. A spectroscopic and electrochemical study on the monomeric precursors revealed the mode of formation of the triple-decker complexes. It has been established that octa-alkyl cadmium phthalocyanines unexpectedly exist very predominantly as dimeric structures in CH₂Cl₂ and these are proposed to be intermediates in the formation of the triple-decker complexes. Results from a series of cross experiments using differently substituted Pcs indicate that cadmium can be scrambled between a CdPc and a metal-free Pc. Furthermore, when either species is added to a solution of a triple-decker complex, the ligand from the added species becomes incorporated into new "mixed" triple-decker complexes. From these results it is proposed that the triple-decker structures are formed by self-assembly processes and that they can disassemble and reassemble in the solution phase. Preliminary measurements have identified ring substitution patterns that lead to higher oligomers.

Three approaches to the synthesis of reduced derivatives of tetraazaporphine such as tetraazachlorin, tetraazabacteriochlorin, and tetraazaisobacteriochlorin are reviewed. The first synthesis of alkyl-substituted tetraazachlorins was achieved by the catalytic hydrogenation of magnesium complexes of tetraazaporphines. Two other synthesis approaches for reduced tetraazaporphines based on the mixed condensation of the precursors with different hydrogenation levels and β–β addition reactions have been developed in the last decade. The use of tetramethylsuccinonitrile as the saturated component in the mixed condensation with derivatives of aromatic and heteroaromatic dicarboxylic acids enable the synthesis of oxidation-resistant benzo-; 1,2- and 2,3-naphtho-; pyrazino-; 2,3- and 3,4-pyridino-fused tetraazachlorins, tetraazabacteriochlorins, and tetraazaisobacteriochlorins. Fullerene conjugates of reduced tetraazaporphine derivatives were obtained using 1,2-dicyanofullerene as the source of the hydrogenated sites. Tetraazaporphine can act as dienophile in Diels-Alder reaction with dienes of the anthracene and cyclopentadiene series and also as dipolarophile in 1,3-dipolar cycloadditions with azomethine ylides and nitrones. In addition, the effect of the reduction of peripheral double bonds in tetraazaporphine macrocycle alone, and in combination with annelation of benzene or heterocyclic rings on the absorption spectra is discussed.

We report here on the synthesis, isolation and characterization of unsymmetrically substituted subphthalocyanines obtained from the mixed condensation of 4,5-substituted phthalonitriles and/or 4-substituted phthalonitriles in the presence of BCl₃. Compared to phthalocyanines, it is clear that the cone-shaped structure of subphthalocyanines facilitates the isolation of the different regioisomers formed by regular laboratory chromatographic techniques. However, we demonstrate that some factors, such as the solubility of the regioisomers formed or the intermolecular interactions between side chains, can sometimes impede their complete separation. We also show that the structural assignment of each regioisomeric compound can be performed by careful analysis of its ¹H NMR spectra and, in some cases, with the help of NOE NMR experiments and molecular modeling.

A unique class of azo porphyrin, 5,10,15,20-tetraphenyl-21-phenylazo-(2-aza-21-carbaporphyrin 1, in which an azophenyl group is embedded in N-confused porphyrin, was synthesized and characterized by ¹H NMR, ¹³C NMR, UV-vis absorption, MS, and X-ray crystallographic analysis. Synthesis of 1 was achieved through a coupling reaction of 21-amino N-confused tetraphenylporphyrin with nitrosobenzene and subsequent deoxygenation of resulting azoxy derivative with a trioxo rhenium(VII) N-fused porphyrinato catalyst. The azo-conjugate molecule was exclusively obtained as a trans-isomer and no isomerization to the cis-isomer was observed under thermal or photoirradiation. The absorption spectrum of 1 shows a moderate red-shift due to the effective interaction between the porphyrinic π-system and the connecting azophenyl group. Upon protonation, this effect is essentially lost as a result of removing degeneracy of LUMO and LUMO+1.

The condensation reaction of 2-amino-3-[(3-pyridylmethyl)amino]-2(Z)-butene-1,4-dinitrile with a series of diketones led to novel dinitriles, of which 2-(2,5-dimethyl-1H-pyrrol-1-yl)-3-[methyl(3-pyridylmethylene)amino]-2(Z)-butene-1,4-dinitrile, the product of the Paal-Knorr reaction, was successfully utilized in the Linstead macrocyclization towards symmetrical and unsymmetrical porphyrazines. NMR and X-ray study revealed an almost perpendicular orientation of the pyrrolyl groups in relation to the porphyrazine platform. The newly synthesized macrocycles with different peripheral groups show interesting spectroscopic and electrochemical properties. Due to selective sensor/coordination properties they are expected to find applications as chemical sensors and electronic materials.

Phthalocyanines present a flat, disk-like molecular profile and suitably substituted derivatives show discotic liquid crystalline behavior. Extension of the molecular π-system through benzofusion perturbes the phthalocyanine's basic properties, most notably shifting the absorption to longer wavelength. This paper describes our synthesis of triphenylenophthalocyanines where the benzene rings of phthalocyanines are replaced by triphenylene units. The resulting materials are macrodiscotic in nature. They show red-shifted absorption spectra and columnar mesophase behavior over a wide temperature range.

The reaction of carbohydrate-substituted α-diazoacetates with meso-tetrakis(pentafluorophenyl)porphyrinatozin(II) allows the synthesis of new glyco-hydroporphyrin derivatives.

gem-dimethylisocorrole gave four-coordinate Ni(II) and Cu(II) complexes, five-coordinate (chloro)Fe(III) and (chloro)Mn(III) complexes, and six-coordinate (chloro)(pyridinato)Rh(III) complex in moderate to good yields. The dinuclear complexes such as the μ-oxo-diiron(III) complex and tetracarbonyldirhodium(I) complex were also prepared. The structures of these mononuclear and dinuclear complexes were determined by X-ray crystallography. These structures are very similar to those of the corresponding metaloporphyrins but the presence of the sp³-meso carbon allows tilting of the pyrrole rings so as to adapt itself to various metal coordination geometries.

The synthesis and characterization of two novel tetrasubstituted zinc phthalocyanines bearing bulky alkylaryloxy substituents in the so-called peripheral (1) and non-peripheral (2) positions is reported. Due to the presence of these bulky substituents, the non-peripheral substituted ZnPc2 can be isolated as a pure regioisomer just by column chromatography. This is the first case where an α,α,α,α-tetrasubstituted regioisomer is isolated by column chromatography. Moreover, we describe the supramolecular complexation of both Pcs with the new pyridine-substituted trinitrofluorenone derivative TNFPy (3), whose synthesis and characterization is also commented. ¹H NMR titration experiments show that the system 2/3 presents a binding constant 35 times higher than system 1/3, which suggests a better accessibility to the metallic center.

Novel heteropentameric porphyrins-pyrene arrays, in which four meso-tetraphenyl porphyrins are linked to the center unit of pyrene by four acetylenyl bonds, were designed and synthesized. The newly synthesized heteropentameric compounds have been characterized by a wide range of spectroscopic methods. The third-order nonlinear optical (NLO) properties of both the metal-free and zinc compounds of the three-dimensional arrays were investigated by Z-scan experiments, showing enhanced NLO properties compared with that of the porphyrin and pyrene monomers.

A novel one-pot method for the regioselective preparation of early heteroleptic lanthanide (porphyrinato)(phthalocyaninato) complexes of double- and triple-decker structure [(Por)Ln(Pc) and (Por)Ln(Pc)Ln(Por), respectively] is developed. Sandwich-type complexes are synthesized for La, Ce and Pr following this procedure, with yields up to 30%. Tetrakis(15-crown-5)-phthalocyanine [(15C5)₄PcH₂] and tetrakis-meso-(4-methoxyphenyl)-porphyrin (An₄PH₂) are used as macrocyclic tetrapyrrolic ligands. The complexes are widely characterized with various physico-chemical methods (NMR and UV-vis spectroscopy, MALDI-TOF mass spectrometry). Quantum chemistry calculations for intermediates of the process are performed. The results of calculations explain the high regioselectivity of the triple-decker complex formation in the developed method.