Meso-nitrogen Atoms Research Articles

Indium(III) complexes of octaphenylporphyrazine: Effect of halide coordination on the basic properties and stability in acid media

Influence of halide ion coordination on the basic properties and stability of indium(III) octaphenylporphyrazine complexes in acid medium have been studied. Five-coordinated halide complexes [(Hal)InPAPh8] (Hal = F, Cl, Br) are stable in dichloromethane or chloroform solutions acidified with trifluoroacetic acid up to 100%. One of four meso-nitrogen atoms is protonated in 0.1 M solution; their basicity depending of the ionic character of In–Hal bond is decreased in the order F > Cl > Br . Addition of an excess of fluoride, chloride or bromide anions leads to formation of anionic cis-dihalide complexes cis [(Hal)2InPAPh8] - which undergo very facile demetalation with formation of the free-base H2PAPh8 even in a slightly acidified solutions (0.001 M of acid). Such catalytic effect of halide anions seems to be general for demetalation reactions of indium(III) complexes with tetrapyrrolic macrocycles and was also observed for the phthalocyanine complex [(Cl)InPc] . Coordination of iodide leads to reduction of porphyrazine macrocycle assisted by meso-protonation with formation of π-anionic species, which upon demetalation and subsequent deprotonation give a mixture of free-base porphyrazine H2PAPh8 and tetraazachlorin derivatives.

Phthalocyanine Analogues: Unexpectedly Facile Access to Non‐Peripherally Substituted Octaalkyl Tetrabenzotriazaporphyrins, Tetrabenzodiazaporphyrins, Tetrabenzomonoazaporphyrins and Tetrabenzoporphyrins

Controlled syntheses of phthalocyanine/benzoporphyrin hybrid structures have been achieved. We report a simple means for obtaining non-peripherally octaalkyl-substituted derivatives of tetrabenzotriazaporphyrin (TBTAP), tetrabenzodiazaporphyrin (TBDAP), tetrabenzomonoazaporphyrin (TBMAP) and tetrabenzoporphyrin (TBP) macrocycles by treating 3,6-dialkyl phthalonitriles with differing amounts of the Grignard reagent MeMgBr. This range of macrocyclic products is not obtained from corresponding reactions of a Grignard reagent with 4-substituted phthalonitriles, reported previously, or reaction of MeMgBr with a 4,5-dialkyl phthalonitrile. Attempts to form a meso-substituted TBTAP from 3,6-dialkyl phthalonitriles by reaction with benzyl and long-chain alkyl Grignard reagents unexpectedly gave only the parent macrocycle unsubstituted at the meso position. The synthetic protocols are by far the most straightforward and convenient means to access these interesting, but scarcely studied, classes of material. The new series of substituted macrocyclic compounds, obtained as the metal-free and magnesium- and copper(II)-metallated derivatives, show trends in the UV/Vis spectra consistent with those predicted elsewhere by Kobayashi. Characterisation of the new families allows further trends to be identified as meso-nitrogen atoms are sequentially replaced by methine bridges, for example, the compounds provide novel examples of macrocyclic structures that show columnar mesophase behaviour. Single-crystal X-ray structure determinations have been obtained for three magnesium-metallated derivatives bearing eight hexyl substituents and constitute the first set of structural data obtained for such a series.

Cyclohexylcyanine: a new aliphatic phthalocyanine analogue

In this report, we present cyclohexylcyanine, a phthalocyanine analogue with two cyclohexane units incorporated into the backbone of the macrocycle; in the free base, the ionizable protons lie on the periphery of the ring, and when metalated with silver the macrocycle binds to the metal via these same meso nitrogen atoms.

New Synthetic Method for Zinc Complexes of 20-Aryltetrabenzo[5,10,15]-triazaporphyrin

Complexes of tetrabenzo[5,10,15,20]tetraazaporphyrins, known as phthalocyanines, are an important class of macrocyclic compounds, which due to their unique properties have found a wide range of applications. The close analogs of phthalocyanines are tetrabenzotriazaporphyrins, in which one of the meso-nitrogen atoms is substituted by a carbon atom. Tetrabenzo[5,10,15]triazaporphyrins are suggested as photoconducting materials,[1] fluorescent markers in medicine,[2,3] and gas sensors.[4] These compounds remain much less synthetically available than phthalocyanines. The first report on the synthesis of tetrabenzo[5,10,15] triazaporphyrin by heating of the mixture of phthalonitrile, 3-methylenephthalimide and copper chloride at 250°C was published in 1938.[5] One of the common methods of synthesis of tetrabenzo[5,10,15]triazaporphyrins, used up to now, is the interaction of phthalonitrile with organomagnesium reagents with following refluxing in highly boiling solvent.[6,7] There is only one communication on the template synthesis of zinc complex of 20-phenyltetrabenzo[5,10,15]triazaporphyrin on the basis of interaction of 1,3-diiminoisoindoline with phenylacetic acid in the presence of template agent (zinc oxide).[8] Here, we propose a new synthetic method for zinc complexes of 20-aryltetrabenzo[5,10,15]triazaporphyrins by the reaction of unsubstituted phthalodinitrile with quaternary salts of triphenylphosphonium in the presence of zinc powder at gradual heating from 200 to 300oC.§

Density functional theory studies of N-protonation of the free base phthalocyanine

The structures and relative energies of twenty-two N-protonated species of the free base phthalocyanine (H 2Pc) have been systematically studied with the density functional theory at the B3LYP/6-31G(d) level of theory. The calculations demonstrated that the N-protonation tends to increase the N–C bonds and the C–N–C angles on the protonation sites. The inner protonation at the isoindole-nitrogen atoms causes significant out-of-plane deformation of the macrocycle, ascribed to the steric hindrance of the central cavity. The relative energies of various protonated species were calculated and compared to deduce the preferred sites for protonation. It was revealed that the outer protonation at the meso-nitrogen atoms is energetically more favorable than the inner protonation at the isoindole-nitrogen atoms. Among the studied twenty-two protonated species, the most stable one is H 6Pc 4+(IS1), for which all the outer meso-nitrogen atoms are protonated. TDDFT calculations have been performed for selected species, and the results were used to analysis the UV–visible spectrum of the concentrated sulfuric acid solution of the free base phthalocyanine.

Acid base interactions of octaphenyltetrapyrazinoporphyrazine and its complex with lutetium(III) in proton-donor media

Acid base interactions of octaphenyltetrapyrazinoporphyrazine and its complex with lutetium(III) in acetic and trifluoroacetic acid media were studied, and parameters characterizing equilibria between the acid and base forms were determined. Acid-base interactions of octaphenyltetrapyrazinoporphyrazine involve primarily nitrogen atoms in the pyrazine fragments, while its lutetium(III) complex undergoes protonation at the meso-nitrogen atoms.

Study of basic properties of tert-butyl-substituted tribenzo(1,2,5-thiadiazolo)porphyrazines

Basic properties of tri(4-tert-butylbenzo)[b,g,l](1,2,5-thiadiazolo)[3,4-q]porphyrazine and its Cu complex in the H2SO4-CH3COOH medium were studied by means of spectrophotometric titration. It was found that in going from an acetic acid solution 100% H2SO4 the complete acid-base interaction consecutively involves all the four meso-nitrogen atoms of the porphyrazine macroring, as well as one of the nitrogen atoms of the 1,2,5-thiadiazol fragment. The stability constants of the resulting acid forms were determined and compared with the gas-phase proton affinities calculated by the AM1 method. Annulation of a 1,2,5-thiadiazole fragment to the porphyrazine macroring increases the basicity of the 1,2,5-thiadiazole nitrogen atoms and decreases the basicity of macroring meso-nitrogen atoms.

Tetrakis(thiadiazolo)porphyrazines. 3. Acid-base Properties and Stability of Tetrakis-3,4-(1,2,5-thiadiazolo)porphyrazine in Sulfuric Acid Solutions

AM1 calculations gave the proton affinities of different types of donor sites in tetrakis-3,4-(1,2,5-thiadiazolo)porphyrazine, H2{[SN2)4PA}, and protonation of the meso-nitrogen atoms was found to be favored. A spectrometric study showed that the basicity of the meso-nitrogen atoms of the porphyrazine macrocycle is strongly diminished and these atoms in CF3CO2H are involved in an incomplete acid-base interaction (ABI) to give acid solvates, while a complete ABI (protonation) is found only in the presence of sulfuric acid. The basicity constants of the meso-nitrogen atoms were determined spectrophotometrically in CF3CO2H-H2SO4. The kinetics of decomposition of the macrocyclic chromophore in concentrated sulfuric acid was studied and a possible mechanism for this process was proposed.

Study of acid-base interactions of mono- and diazaporphyrin indium complexes with acetic and trifluoroacetic acids by 1H NMR and electronic spectroscopy

Indium complex of 13,17-dibutyl-2,3,7,8,12,18-hexamethyl-5-azaporphyrin (Cl)InMAP was synthesized, and acid-base interactions of the meso-nitrogen atoms in (Cl)InMAP and its diaza analog (Cl)InDAP with acetic and trifluoroacetic acids were studied by 1H NMR and electronic spectroscopy. Depending on the medium, the complexes and proton-donor species HA give rise to acid solvates >N⋅⋅⋅(HA)n which are converted to final acid-base interaction products, H-complexes >N⋅⋅⋅H+⋅⋅⋅A−(HA)m or ionic associates >NH+⋅⋅⋅A−(HA)l , as the acidity of the medium rises. In acetic acid solution, the acid solvates derived from more basic (Cl)InMAP exist in equilibrium with the H-associates (pK a1 = 4.45±0.03). From (Cl)InDAP, the corresponding H-associates are formed only in the presence of H2SO4 (pK a1 = 2.10±0.03). In more polar media (solutions of trifluoroacetic acid in methylene chloride), ionic associates are formed, which involve one [(Cl)InMAP, pK 1 = 2.46±0.02] or two meso-nitrogen atoms [(Cl)InDAP, pK 1 = 2.11±0.03, pK 2 = 0.41±0.04).

Importance of the C-H...N weak hydrogen bonding on the coordination structures of manganese(III) porphyrin complexes.

The reactions between Mn(Por)Cl and Bu(4)N(+)CN(-) have been examined in various solvents by UV-vis and (1)H NMR spectroscopy, where Por's are dianions of meso-tetraisopropylporphyrin (T(i)PrP), meso-tetraphenylporphyrin (TPP), meso-tetrakis(p-(trifluoromethyl)phenyl)porphyrin (p-CF(3)-TPP), meso-tetramesitylporphyrin (TMP), and meso-tetrakis(2,6-dichlorophenyl)porphyrin (2,6-Cl(2)-TPP). Population ratios of the reaction products, Mn(Por)(CN) and [Mn(Por)(CN)(2)](-), have been sensitively affected by the solvents used. In the case of Mn(T(i)PrP)Cl, the following results are obtained: (i) The bis-adduct is preferentially formed in dipolar aprotic solvents such as DMSO, DMF, and acetonitrile. (ii) Both the mono- and bis-adduct are formed in the less polar solvents such as CH(2)Cl(2) and benzene though the complete conversion to the bis-adduct is achieved with much smaller amount of the ligand in benzene solution. (iii) Only the mono-adduct is formed in CHCl(3) solution even in the presence of a large excess of cyanide. (iv) Neither the mono- nor the bis-adduct is obtained in methanol solution. The results mentioned above have been explained in terms of the C-H.N and O-H.N hydrogen bonding in chloroform and methanol solutions, respectively, between the solvent molecules and cyanide ligand; hydrogen bonding weakens the coordination ability of cyanide and reduces the population of the bis-adduct. The importance of the C-H.N weak hydrogen bonding is most explicitly shown in the following fact: while the starting complex is completely converted to the bis-adduct in CH(2)Cl(2) solution, the conversion from the mono- to the bis-adduct is not observed even in the presence of 7000 equiv of Bu(4)N(+)CN(-) in CHCl(3) solution. The effective magnetic moments of the bis-adduct has been determined by the Evans method to be 3.2 micro(B) at 25 degrees C, suggesting that the complex adopts the usual (d(xy))(2)(d(xz), d(yz))(2) electron configuration despite the highly ruffled porphyrin core expected for [Mn(T(i)PrP)(CN)(2)](-). The spin densities of [Mn(T(i)PrP)(CN)(2)](-) centered on the pi MO have been determined on the basis of the (1)H and (13)C NMR chemical shifts. Estimated spin densities are as follows: meso-carbon, -0.0014; alpha-pyrrole carbon, -0.0011; beta-pyrrole carbon, +0.0066; pyrrole nitrogen, -0.022. The spin densities at the pyrrole carbon and meso nitrogen atoms are much smaller than those of the corresponding [Mn(TPP)(CN)(2)](-), which is ascribed to the nonplanar porphyrin ring of [Mn(T(i)PrP)(CN)(2)](-). This study has revealed that the C-H.N weak hydrogen bonding is playing an important role in determining the stability of the manganese(III) complexes.

Manganese Complexes with Octaphenyltetraazaporphine: Acid–Base Interactions and Kinetic Stability in Proton-Donor Solvents

Complexes of manganese(III) and manganese(V) with octaphenyltetraazaporphine (H2OPTAP) were synthesized. Acid–base interactions of these complexes in the CH2Cl2–CF3COOH system and kinetics of their dissociation in concentrated sulfuric acid, as well as kinetics of octaphenyltetraazaporphine destruction in sulfuric acid solutions were studied by spectrophotometric methods. Acid–base interactions in CH2Cl2–CF3COOH were shown to involve two macrocyclic meso-nitrogen atoms in succession. Concentration stability constants of the acid forms obtained pK1 = 0.29 ± 0.01 and pK2 = –0.62 ± 0.08 for (chlorine)manganese(III)octaphenyltetraazaporphine ((Cl)MnOPTAP); pK1 = 0.99 ± 0.02 and pK2 = – 0.70 ± 0.03 for (nitrido)manganese(V)octaphenyltetraazaporphine ((N)MnOPTAP). The rate of dissociation of the complexes in 94–98% H2SO4 does not depend on the acid concentration. The manganese(V) complex is three times as stable as the manganese(III) complex.

Kinetic Stability of Indium(III) Complexes with Azaporphyrins in Aqueous Sulfuric Acid

Stability of chloro(octaphenyltetraazaporphinato)indium(III) and chloro(2,8,12,18-tetrabutyl-3,7,13,17-tetramethyl-5,15-diazaporphinato)indium(III) in 90-98 % aqueous sulfuric acid was studied. Kinetic parameters of solvoprotolytic dissociation of the complexes were determined, and a mechanism of the reaction was proposed. Diaza substitution results in more stable complexes than tetraaza substitution. The state of chloro(2,8,12,18-tetrabutyl-3,7,13,17-tetramethyl-5,15-diazaporphinato)indium(III) in a proton-donor medium was studied to show that the acid-base interaction involves one by one two meso-nitrogen atoms. Dissociation constants of the resulting acid forms were determined.

Azaporphyrins and Phthalocyanines as Multicentre Conjugated Ampholites

Molecules of azaporphyrins combine two acidic pyrrole-type NH groups and several basic centres—two internal pyrrolenine nitrogen atoms and from one to four meso-nitrogen atoms—in one highly conjugated aromatic system. The acid–base properties of such unique multicentre ampholites have been the subject of numerous studies and discussions. Along with a short critical historical review the paper presents the latest results of a systematic investigation of the influence of successive aza substitution on the spectral properties and thermodynamic stability of the acid–base forms of azaporphyrins.