Electrochemical Investigation on Porphyrazines with Peripheral Crown-Ether Groups

Summary.  In this study, the electrochemical properties of novel porphyrazines with eight crown ether substituents appending on the periphery through flexible chains were investigated by using cyclic voltammetry and controlled potential coulometry. Cyclic voltammetry measurements showed that the metal free porphyrazine gave all of the six possible redox reactions of common porphyrazine derivatives. Cobalt porphyrazine exhibited a metal-based reduction and a metal-based oxidation processes followed by two ligand-based reduction and two oxidation processes. I _p vs. ν^1/2 plots of redox processes of the two compounds indicated the diffusional mass transfer mechanism of the complexes. Copper porphyrazine gave an oxidation process having adsorption properties and three reduction reactions. The variations of peak current ratios of electrochemical reactions for all three complexes with scan rate showed that electron transfer processes of complexes were followed by reversible or irreversible chemical reactions. Aggregation and sandwich adduct formation properties of complexes were determined by CV measurements. Peak potentials of redox processes for all complexes were shifted towards positive potentials by addition of alkali metal cations. Addition of K⁺ formed sandwich type adducts with 15-crown-macrocycles diminishing aggregation of planar molecules by intramolecular rather than intermolecular complexation. Corresponding author. E-mail: ahmetg@itu.edu.tr Received May 23, 2002; accepted (revised) May 31, 2002     

Kinetic characteristics of the destruction of β,β-annelated porphyrazines in a nitrogen-containing base–dimethylsulfoxide system

The state of tetra(1,2,5-thiadiazolo)porphyrazine in a dimethyl sulfoxide medium is investigated. Relatively high stability is observed for the resulting proton-transfer complex, and a chemical structure is proposed for it. It is shown that the nature of the substituent in the porphyrazine macrocycle influences the kinetic parameters of the destruction of tetra(1,2,5-thiadiazolo)porphyrazine, tetra(5-tert-butylpyrazino) porphyrazine, octaethyltetrapyrazinoporphyrazine, and octaphenyltetrapyrazinoporphyrazine in a nitrogen-containing base–dimethylsulfoxide system. The effect the NH acidity of the porphyrazine macrocycle and the nature of the nitrogenous bases have on the reaction rate and activation parameters of the destruction of β,β-annelated porphyrazine proton-transfer complexes is established.     

Synthesis and spectral properties of 1,2,5-thiadiazolo-, 1,2,5-selenadiazolo-, and benzo-fused β-phenyl-substituted porphyrazines

Cross cyclotetramerization of trans-2,3-diphenylbutanedinitrile with 1,2,5-thia(selena)diazole-3,4-dicarbonitriles or phthalodinitrile in the presence of magnesium butoxide gave mixtures of Mg(II) porphyrazine complexes which were treated with trifluoroacetic acid to isolate unsymmetrical hexaphenyl-substituted 1,2,5-thia(selena)diazolo-and benzo-fused porphyrazines together with diphenyltribenzoporphyrazine. Their ¹H NMR and electronic absorption spectra (in the UV and visible regions) were recorded. The effect of benzene and heteroring fusion on the electronic and steric structure and spectral properties of porphyrazine derivatives was studied in terms of the molecular orbital perturbation theory and semiempirical quantum-chemical calculations (AM1, PM3, ZINDO/S, CNDO/S).     

Electrochemical Investigation on Porphyrazines with Peripheral Crown-Ether Groups

 In this study, the electrochemical properties of novel porphyrazines with eight crown ether substituents appending on the periphery through flexible chains were investigated by using cyclic voltammetry and controlled potential coulometry. Cyclic voltammetry measurements showed that the metal free porphyrazine gave all of the six possible redox reactions of common porphyrazine derivatives. Cobalt porphyrazine exhibited a metal-based reduction and a metal-based oxidation processes followed by two ligand-based reduction and two oxidation processes. I _p vs. ν^1/2 plots of redox processes of the two compounds indicated the diffusional mass transfer mechanism of the complexes. Copper porphyrazine gave an oxidation process having adsorption properties and three reduction reactions. The variations of peak current ratios of electrochemical reactions for all three complexes with scan rate showed that electron transfer processes of complexes were followed by reversible or irreversible chemical reactions. Aggregation and sandwich adduct formation properties of complexes were determined by CV measurements. Peak potentials of redox processes for all complexes were shifted towards positive potentials by addition of alkali metal cations. Addition of K⁺ formed sandwich type adducts with 15-crown-macrocycles diminishing aggregation of planar molecules by intramolecular rather than intermolecular complexation.     

Electronic structure and optical properties of a tin-encapsulated nickel porphyrazine compound

The recently synthesized metal-encapsulated porphyrazine compound, [Sn(t-Bu)₂]₄-star-Ni(porphyrazine)-S₈, shows very interesting structural and optical absorption features compared with other metal-centered porphyrazines, e.g., metal phthalocyanines (Pc). Using self-consistent-field local density theory, we studied the ground-state and excited-state electronic structure of this molecule and compared it with its metal phthalocyanine analog NiPc. The theoretical optical spectra including oscillator strengths are in good agreement with experimental absorption and show that the characteristic transitions at the so-called Soret band in NiPc are red-shifted in the new compound. © 1994 John Wiley & Sons, Inc.     

Esterified porphyrazine complexes: Synthesis,characterization, aggregation behavior,and theoretical study

Magnesium porphyrazine having eight 5-hydroxypentylthio groups at the peripheral positions, was synthesized from 2,3-bis(5-hydroxypentylthio) maleonitrile. By the esterification reaction of octakis(5-hydroxypentylthio) porphyrazinato] Mg(II) with 3,4,5-trimethoxybenzoic acid in dicyclohexylcarbodiimide and toluene-p-sulfonic acid, esterified MgPz appending [5-thiopentyl 2-methoxy-4,6-bis(trifluoromethyl) benzoate] substituent was obtained. Further reaction of the metal-free porphyrazine with Co(II), Cu(II), Zn(II), and Fe(II) acetates have produced the metallo-porphyrazines. By reacting FePzCl with pyridine or pyrazine, the monomeric bis-axial and the oligomeric complexes were synthesized as the novel stable complexes, respectively. Their characterizations were performed by using elemental analysis, FT-IR, ¹H-NMR, ¹³C-NMR, mass and UV-Vis spectral data. The aggregation investigations carried out in different concentrations indicate that 3,4,5-trimethoxybenzyloxy-substituted porphyrazine compounds do not have any aggregation behavior in different concentrations. Quantum chemical computations were also done to the structural and electronic properties of target compounds.     

Kinetic stability of substituted tetrapyrazinoporphyrazines in a system nitrogen base-dimethylsulfoxide

The state of tetra(5-tert-butylpyrazino)porphyrazine, octaethyltetrapyrazinoporphyrazine, octaphenyltetrapyrazinoporphyrazine in DMSO medium was studied. It was found that the complexes formed with the proton transfer exhibit a relatively high stability. In strong basic media these complexes are kinetically unstable. The influence of the nature of cyclic and acyclic nitrogen-containing bases, as well as the influence of NH-acidity of the porphyrazine macrocycle on the rate and activation parameters of decomposition of the proton-transfer complexes of tetra(5-tert-butylpyrazino)porphyrazine, octaethyltetrapyrazinoporphyrazine, and octaphenyltetrapyrazinoporphyrazine was established.     

N-Aryl diketopyrrolopyrrole derivatives towards organic optical and electronic materials

Diketopyrrolopyrrole (DPP) and related derivatives have drawn great attention due to their applications in organic optical /electronic materials. Progress in these materials is associated with developments in the syntheses of the DPP family. Chemical modification of DPP at nitrogen atom, including N-alkylation and N-arylation, is an effective strategy to improve its physical and chemical properties, such as solubility, optical and semiconducting properties. However, N-arylation of DPPs remains challenging compared to the easily accessible N-alkylation. Herein, the synthesis of N-aryl DPP derivatives and correlated π-expanded DPPs are summarized, and their optical/electronic properties are introduced. The future perspectives of N-aryl DPP derivatives are also discussed.     

Serendipitous synthesis of trimetallic porphyrazine triads

We report the synthesis and characterization of structurally unusual porphyrazine triads with three macrocycles bound to a central pyrazine core. These trimacrocyclic complexes were accidentally discovered during studies on the peripheral metallation of porphyrazinediamines. The crystal structure of the tri-zinc porphyrazine triad is described and the spectroscopic properties including electronic absorption spectra of this complex and the corresponding magnesium, free-base, and copper derivatives are reported.     

Acid-base properties of thianaphthene-annulated porphyrazine and tetra(pyrazino)porphyrazine complexes with aluminum group metals

Acid-base properties of Al(III), Ga(III), and In(III) complexes with tert-butyl-substituted thianaphthene-annulated porphyrazine and tetra(2,3-pyrazino)porphyrazine in proton-donor medium (CH₂Cl₂-CF₃COOH) were studied by spectrophotometric titration. The concentration stability constants of the singly protonated complexes were determined. The effects of the metal nature and aromatic heterocyclic fragment on the basicity of meso-nitrogen atoms were analyzed. Negative inductive effect of the sulfur atom in the thianaphthene fragment reduces the basicity of the meso-nitrogen atoms as compared to analogous porphyrazine and phthalocyanine complexes. Acid-base transformations of the thianaphthene-annulated tetra(2,3-pyrazino)porphyrazine involve both meso-nitrogen atoms and those in the pyrazine rings.     

Molecular Receptors. Functionalized and chiral macrocyclic polyethers derived from tartaric acid

A number of functionalized and chiral macrocyclic polyethers have been synthesized by condensation of the dithallium alcoholate of (R,R)-(+)-tartaric acid derivatives with α, ω-dihalides. In this way for instance, the tetracarboxylic [18]-O₆ macrocycle 3c and its derivatives become readily available. They form complexes with various cationic substrates. NMR. and crystal-structure data provide information about the orientation of the side chains X in 3 with respect to the macrocycle. It is concluded that in the secondary amides like 3b and in their complexes the four X-groups are preferentially in an axial orientation on the average. This property is of much significance for the design of molecular receptors and catalysts based on this macrocyclic structure. The preparation of a number of other macrocycles is also described.     

Study of acidic and complexing properties of tetraphenylporphyrazine and octa(4-bromophenyl)porphyrazine in DMSO at 298 K

The acid dissociation of tetraphenylporphyrazine (H₂PA(Ph)₄) and octa(4-bromophenyl)porphyrazine (H₂PA(4-BrPh)₈) and their reactions with Cd²⁺ ions were studied in DMSO at 298 K. The equilibrium formation constants of the complexes and the acid dissociation constants of porphyrins were calculated; their relationship with the stability constants of the complexes was analyzed. The acidity sequence for porphyrazine derivatives was established.     

Investigation of unsubstituted porphyrazine by proton NMR and the structure of porphyrazine ligands

The proton NMR spectra of unsubstituted porphyrazine (tetraazaporphine) and of its Zn complex in pyridine-D₅ and in CF₃COOD have been obtained for the first time. The observed strong deshielding of the pyrrole hydrogen atoms of these compounds compared with porphyrins indicates the existence of strong intramolecular hydrogen bonds with neighboring pyrrolenic nitrogen atoms. An unsymmetrical bridge structure is proposed for the reaction center of unsubstituted porphyrazine with significantly ionized N?H bonds. It is suggested that a symmetrical bridge structure almost completely ionized, may exist only in the presence of such strong electron-accepting substituents as halogen in the pyrrole rings of the porphyrazine macrocycle.     

New promising porphyrazine-based agents for optical theranostics of cancer

New porphyrazine bases containing peripheral benzyloxyphenyl groups have been synthesized by the template method. The procedure includes condensation of aromatic aldehydes with malononitrile, transformation of arylmethylidenemalononitriles to arylethenetricarbonitriles, template assembly of porphyrazine macrocycle on bis(indenyl)ytterbium(II) complex, and removal of the central metal ion. Luminescence properties of the synthesized porphyrazines and their dependence on the viscosity of the medium were studied, and the light and dark toxicities of the porphyrazines have been estimated. The obtained results suggest the possibility of using these porphyrazines as optical theranostic agents of new generation.     

Kinetics of the formation and dissociation of complexes of cobalt(II) with <Emphasis Type="Italic">meso</Emphasis>-Phenylocta(methyl)porphyrin derivatives in organic solvents

The influence of the deformation of the tetrapyrrole aromatic macrocycle and the electronic effects of substituents on the kinetic parameters in the formation and dissociation reactions of cobalt complexes of porphyrins are discussed on the basis of a study of the kinetics of the formation and dissociation of cobalt complexes with meso-phenyl octa(methyl)porphyrin derivatives: 5,10,15-triphehyl octa(methyl) porphyrin; 5,15-bis-(3′,5′-di-tert-butyl phenyl) octa(methyl)porphyrin; 5,10,15-tris-(3′,5′-di-tert-butyl phenyl) octa(methyl)porphyrin; and 5,10,15,20-tetrakis-(3′,5′-di-tert-butyl phenyl) octa(methyl)porphyrin in acetic acid and pyridine.     

Synthesis and Metalation of Doubly o‐Phenylene‐Bridged Cyclic Bis(dipyrrin)s with Highly Bent Skeleton of Dibenzoporphyrin(2.1.2.1)

Facile synthesis of dibenzoporphyrins(2.1.2.1) has been successfully reported by the simple condensation reaction of o‐dipyrrolylbenzene with various aldehydes in the presence of a Lewis acid. This reaction enables the preparation of various dibenzoporphyrin(2.1.2.1) derivatives with p‐substituted phenyl groups, five‐membered heterocycles, and ethynyl groups at the meso‐positions. Dibenzoporphyrins(2.1.2.1) consist of two dipyrrin units that are connected by o‐phenylene bridges, which adopt highly bent saddle‐shaped structures; this was confirmed by X‐ray diffraction analysis. We found that dibenzoporphyrin(2.1.2.1) can be described as a 20π antiaromatic conjugated system, but practically, it is not an antiaromatic macrocycle, which we revealed by ¹H NMR spectroscopy. The redox potentials had good correlations with Hammett substituent constant (σ_p) of the substituents at the meso‐positions. The free‐base dibenzoporphyrin(2.1.2.1) was able to form the metal complexes with nickel(II), copper(II), palladium(II), platinum(II), and tin(IV) ions. These results suggested that dibenzoporphyrin(2.1.2.1) derivatives can be utilized as novel macrocyclic dianionic tetradentate ligands for various metal ions to give complexes with varying optical and electrochemical properties.     

Meso-Carbon Atom Nucleophilic Attack Susceptibility in the Sterically Strained Antiaromatic Bis-BODIPY Macrocycle and Extended Electron-Deficient BODIPY Precursor**

A sterically strained 32π-electron antiaromatic bis-BODIPY macrocycle in which two BODIPY fragments are linked by p-divinylbenzene groups was prepared and characterized. Unlike regular BODIPYs, the fluorescence in this macrocycle is quenched. The broad signals in the NMR spectra of the macrocycle were explained by the vibronic freedom of the p-divinylbenzene fragments. The possible diradicaloid nature of the macrocycle was excluded on the basis of variable-temperature EPR spectra in solution and in solid state, which is indicative of its closed-shell quinoidal structure. The meso-C−H bond in the macrocycle and its precursor BODIPY dialdehyde 3 forms a weak hydrogen bond with THF and is susceptible for the nucleophilic attack by organic amines and cyanide anion. The reaction products of such a nucleophilic attack have meso-sp³ carbon atoms and were characterized by NMR, mass spectrometry and, in one case, X-ray crystallography. Unlike the initial bis-BODIPY macrocycle, the adducts have strong fluorescence in the 400 nm region. The electronic structure and spectroscopic properties of new chromophores were probed by density functional theory (DFT) and time-dependent DFT (TDDFT) calculations and correlate well with the experimental data.     

Metal-free,metallo-porphyrazines,monomeric bisaxial complex [FePz(py)2] and the bridged complex [FePz(pyz)]n with eight (4-thiobutyl 4-biphenylcarboxylate) groups

Metal-free and metallo-porphyrazines (M?=?Mg, Co, Cu, Zn, and ClFe) carrying eight hydroxybutylthio groups at peripheral positions were prepared from 2,3-bis(4-hydroxybutylthio) maleonitrile. The hydroxybutyl groups were incorporated by esterification of porphyrazine derivatives with 4-biphenylcarboxylic acid in the presence of dicyclohexylcarbodiimide and p-toluenesulfonic acid. Unlike the parent porphyrazine, the symmetrically functionalized porphyrazines with eight ester units were soluble in common organic solvents such as chloroform, dichloromethane, tetrahydrofuran, acetone, and toluene and insoluble in water and n-hexane. Chloro-octakis(4-thiobutyl 4-biphenylcarboxylate) porphyrazinato iron(III) (FePzCl) was prepared by the reaction of metal-free porphyrazine with iron(II) acetate and further treatment with HCl solution. The monomeric bisaxial complex [FePz(py)₂] and the bridged complex [FePz(pyz)]_n were formed as stable complexes by reacting FePzCl with pyridine and pyrazine, respectively. The newly synthesized compounds were characterized by elemental analysis, FT-IR, UV?vis, mass, ¹H and ¹³C NMR spectroscopy.     

Enhancing the Acceptor Character of Conjugated Organoborane Macrocycles: A Highly Electron-Deficient Hexaboracyclophane

We introduce a new boron-doped cyclophane, the hexabora[1₆]cyclophane B6-^FMes , in which six tricoordinate borane moieties alternate with short conjugated p-phenylene linkers. Exocyclic 2,4,6-tris(trifluoromethyl)phenyl (^FMes) groups serve not only to further withdraw electron density but at the same time sterically shield the boron atoms, resulting in a macrocycle that is both highly electron-deficient and stable. The optical and electronic properties are compared with those of related linear oligomers and the electronic structure is further evaluated by computational methods. The studies uncover unique properties of B6-^FMes , including a low-lying and extensively delocalized LUMO and a wide HOMO–LUMO gap, which arise from the combination of a cyclic π-system, strong electronic communication between the closely spaced borons, and the attachment of electron-deficient pendent groups. The binding of small anions to the electron-deficient macrocycle and molecular model compounds is investigated and emissive exciplexes are detected in aromatic solvents.     

Bromination of Tetraazaporphine and Its β-Substituted Derivatives Using Pyridine as Solvent and Catalyst

The selectivity and degree of bromination of pyrrole rings in porphyrazine strongly depends on the brominating agent and solvent nature. The reaction of porphyrazine magnesium complex with molecular bromine and N-bromosuccinimide in pyridine gave magnesium complex of dibromotetraazaporphine. Increasing bromine substitution in porphyrazine enhances its acidic properties.