The state of 5,10,15,20-tetraphenyl-21H,23H-porphine rhenium(V) complexes in solutions of acids

The spectral properties (UV/Vis, IR, ¹H NMR) and stability of diverse forms of 5,10,15,20-tetraphenyl-21H,23H-porphine rhenium(V) complexes in neutral and protolytic solvents have been studied. Quantitative characteristics have been obtained for the reactions of formation and interconversion of the μ-oxo dimeric and monomeric rhenium(V) complex species in the benzene-AcOH system and dissociation at the coordination center of the H⁺-associated form of the monomeric rhenium(V) complex in mixed H₂O-H₂SO₄ solvents in a wide range of component concentrations. It has been shown that the stability of the coordination center of the rhenium(V) complexes sharply depends on the nature of a second acido ligand, in addition to the coordinated porphyrin.     

5,15-bis(4′-methoxyphenyl)-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphin axial complexes of rhenium: Synthesis and reactions in protic solvents

The spectral (UV–Vis, IR, and NMR ¹H) properties and the state of oxorhenium(V) complexes with 5,15-bis(4′-methoxyphenyl)-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphin H₂P (O=Re(X)P) in protic solvents have been studied depending on the axial trans-ligand X^– (X = Cl, OPh, or OH). The O=Re(Cl)P, O=Re(OPh)P, and O=Re(OH)P in AcOH and CF3COOH are subjected to reaction of substitution their axial ligands with solvent molecules or anions, while remaining stable to the dissociation of M–N bonds and to oxidation both to the macrocyclic ligand and to the central metal cation. Quantitative parameters of the coordination of molecular oxygen by O=Re(Cl)P in 17.4–18.2 M H₂SO₄ to form O=Re(O₂)P⁺ · Cl^– have been obtained, these parameters being independent of the initial H₂SO₄ concentration. The character of peripheral functional substituents in H₂P has been shown to be responsible for the stability of the studied oxo complexes to chemical oxidation in aerated acids.     

Synthesis and stability of bis(acetato)(5,10,15,20-tetraphenylporphyrinato)zirconium(IV)

The results of studying a unique synthesis method, the kinetics and mechanism of dissociation in acid media, and the stability of a new octacoordinated zirconium complex with two bidentate acetate ligands and one 5,10,15,20-tetraphenylporphine ligand, (AcO)₂ZrTPP, are presented. The method of synthesis is distinguished by the use of stable ZrOCl₂ in the complex formation reaction, instead of readily hydrolyzed zirconium tetrachloride, in boiling phenol, which exhibits the reduction properties. The UV, visible, IR, and ¹H NMR spectral parameters and the values of chromatographic mobility and stability of the complex are obtained. A protolytic dissociation scheme, which is universal for mixed porphyrin-containing zirconium complexes, is substantiated using data on the dissociation rates of an (Cl)₂ZrTPP analogue, depending on the temperature and acidity of the medium. The scheme includes a trimolecular rate-determining step (the complex ionized at one or both noncyclic ligands and two nonionized sulfuric acid molecules) and kinetically significant equilibria of dissociation of the noncyclic acido ligands and sulfuric acid.     

Ion-molecular interactions in the metalloporphyrin-acid system in liquid solutions

A new form of MP...H _solv ⁺ metalloporphyrins is found and studied in the strong acid medium, the conditions of its formation and the qualitative reaction of its determination are established. It is shown that the same form has the H₄TPP²⁺ dication (TPP is the 5,10,15,20-tetraphenyl-21H,23H-porphyrine dianion). The stability in different acid media and in the isolated state, spectral properties and the structure of H⁺-associates of porphyrins are analyzed in detail by UV-visible and ¹H NMR spectroscopy and quantum chemical calculations. It is shown that they have a unique two-band visible electronic spectrum with the bands near 540 nm and 700 nm, which weakly depend on the type of the central atom in the complex and noticeably change when the chromophore is functionally substituted. The proton location the ion-molecular associate and the cases of the formation of H⁺-associates with higher stoichiometry are revealed.     

Coordination of 5,10,15,20-tetraphenyl-21H,23H-porphin by rhenium in various oxidation states

A method was developed for the synthesis of three rhenium complexes, (5,10,15,20-tetraphenyl-21H,23H-porphinato)(phenoxo)rhenium(III) (PhO)ReTPP, (5,10,15,20-tetraphenyl-21H,23H-porphi-nato)(chloro)rhenium(III) (Cl)ReTPP, and μ-oxo-bis[(oxo)-(5,10,15,20-tetraphenyl-21H,23H-porphi-nato)rhenium(V)] [O=ReTPP]₂O, by one reaction between porphyrin H₂TPP and H₂ReCl₆ in boiling phenol. In the complex formation reaction accompanied by the redox process, only the metal cation is involved in the transformation. Rhenium(IV) as chlororhenic acid dispropoportionates without participation of solvent or porphyrin to give Re(III) and Re(V) complexes. The chemical structures of the products were established by spectral and elemental analysis. Characteristics of the UV, Vis, IR, and ¹H NMR spectra, the chromatographic mobility, and stability of the complexes were determined.     

Thermodynamics and kinetics of the formation of the supramolecular complexes bisacetato(5,10,15,20-tetraphenylporphinate)zirconium(IV) with pyridine and imidazole

The equilibria and rates of step reactions for the formation of the supramolecular complexes of bisacetato(5,10,15,20-tetraphenylporphinate)zirconium(IV) (AcO)₂ZrTPP and bioactive bases pyridine (Py) and imidazole (Im) in toluene were studied using UV-Vis and IR spectroscopy. The step stoichiometric mechanism, including the reversible coordination of two Py molecules (K ₁ = 1.8 × 10⁸ l²/mol²), the equilibrium of the displacement of two AcO⁻ into the second coordination sphere by increasing the concentration of the solvent polar component (K ₂ = 2.4), and the coordination of the third and fourth Py molecules in a one step with the formation of [(Py)₄ZrTPP]²⁺ · 2(AcO)⁻ (K ₃ = 2.8 × 10⁴ l²/mol²), was verified. It was established that the spectrophotometric titration is sensible for the two-stage π-π-complexation of [(Py)₄ZrTPP]²⁺ · 2(AcO)⁻ with Py molecules (K ₄ = 29 l/mol and K ₅ = 1.8 l/mol). It was shown that the stronger base Im reacts irreversibly with (AcO)₂ZrTPP. The thermodynamic and optical characteristics of (AcO)₂ZrTPP required for using the complex in the detection of bioactive bases were studied.     

Variations in functional substitution of the macroheterocycle and structure of stable rhenium(V) porphyrins

Rhenium(V) porphyrin complexes with different natures of substituents and substitution patterns in the organic fragment (5,10,15,20-tetraphenylporphyrin, 2,3,7,8,12,13,17,18-octaethylporphyrin, 2,3,7,8,12,13,17,18-octaethyl-5-phenylporphyrin, and 2,3,7,8,12,13,17,18-octaethyl-5,15-diphenylporphyrin dianions) and different axial ligands {phenoxide and chloride ions, 2′-(pyridin-4-yl)-5′-(pyridin-2-yl)-1′-(pyridin-3-ylmethyl)pyrrolidino[3′,4′: 1,9](C₆₀-I _h)[5,6]fullerene} have been synthesized, and their principal properties (spectral parameters and reactivity toward fullerene-containing base) have been studied.     

Acid-base and coordination properties of some palladium(II)porphyrins

The speciation and reactions of palladium(II) complexes with meso-tetraphenylporphine (H₂TPP) and meso-tetraphenyl-β-octaethylporphine (H₂TetPOEP) were studied in H₂SO₄-H₂O and H₂SO₄-HOAc protic solvents. H-associated species of PdTPP and PdTetPOEP were found to exist in sulfuric acid with concentrations of 16.33–17.38 and 17.48–18.22 mol/L, respectively. The kinetics of one-electron oxidation of complexes in the coordinated aromatic macrocycle were studied. A third-order rate equation was determined, and the mechanism of the oxidation reaction was substantiated with kinetically significant stages of dioxygen coordination, electron transfer from the macrocyclic aromatic system to dioxygen, and H-association equilibrium between the complex and sulfuric acid. The effects of peripheral ethyl substituents in the macrocyclic ligand on the reactivity of palladium(II)porphyrins were revealed.