T. N. Lomova

Porphyrin Complexes with p, d, and fMetals in High Oxidation States: Structures, Electronic Absorption, and IR Spectra

This paper is a review of data obtained by the authors and of the literature data on the molecular structure of porphyrin complexes with p, d, and f metals in oxidation states from two to five and on complexation as revealed from the absorption spectra of porphyrins in UV, visible, and IR regions. It was shown that, depending on the type of donor–acceptor bonds, the EAS of metalloporphyrins can be divided into three groups and classified as common, hypso, or hyper spectra. The high-frequency or low-frequency shifts of bands of metal-sensitive porphyrin vibrations in IR spectra of complexes correlate with the type of electronic spectrum; therefore, they were used to study the electronic aspects of coordination interaction in the porphyrin complexes.

Ruthenium(IV) and Osmium(II) Tetraphenylporphine Complexes: Synthesis and Oxidation Reactions

The Ru(IV) and Os(II) complexes (PhO)2RuTPP and OsTPP were synthesized from tetraphenylporphine (H2TPP) and K2RuO4 or K2OsO4 (taken in the molar ratio of 1 : 30) in boiling phenol. The kinetics of oxidation reactions of these complexes in solutions of HOAc (acetic), H2SO4, and HOAc–H2SO4 acids was studied. It was found that in the aerated HOAc–H2SO4 mixture heated above 340 K, these complexes are oxidized with participation of different reaction sites: the Ru(IV) complex is oxidized at macrocycle to give the π-radical-cation (PhO)2RuТPP•+, while in the Os(II) complex, the metal atom is oxidized to form the Os(III) complex. In the first case, the reaction follows the activation mechanism, whereas in the second case, the activation energy of the reaction is zero.

Mutual Influence of Ligands and Reactivity of Gd and Dy Acidophthalocyaninate Complexes

The results of the kinetic study of dissociation of Gd(III) and Dy(III) complexes with phthalocyanine of the composition (X)LnPc (X is single-charged acido ligand) with isolation of macrocyclic ligand depending on the temperature, composition of mixed ethanol–acetic acid solvent, and the nature of acido ligand are presented. The total kinetic equations, the rate constants, and activation parameters of dissociation reaction are determined. The stoichiomeric mechanism is suggested for the complex dissociation involving the limiting elementary reaction between acetic acid molecule and the complex that occurs as the chelate salt (X)LnPc or the outer-sphere complex [(HOAc)LnPс]+X–. The state of metal phthalocyaninate at the reaction slow stage is shown to be determined by the electronic structure of the metal cation, the strength of binding of the axial ligand, and by its cis-effect on the metal bonds with macrocycle.

The magnetocaloric effect and the heat capacity of aqueous suspensions of porphyrin complexes of rare earth elements according to microcalorimetric data

The magnetocaloric effect (MCE) and heat capacity during the magnetization process of (5,10,15,20-tetraphenylporphyrinato)acetatogadolinium(III), (AcO)GdTPP, and (5,10,15,20-tetraphenylporphyrinato)chlorogadolinium(III) complexes, (Cl)GdTPP, in the form of 6%-aqeous suspensions are determined by the microcalorimetric method in a range of temperatures from 278 to 318 K and magnetic fields from 0 to 1 T. It is found that MCE for all the complexes are positive, i.e., at applying a magnetic field in the adiabatic conditions temperature of a suspension of complex increases. It is established that MCE increases with an increase in magnetic induction at all temperatures and decreases with an increase in temperature at all magnetic fields. It is shown that the substitution of chloride ligand by acetate in (X)GdTPP leads to a significant increas in MCE and its temperature dependence; in the case of (Cl)GdTPP actually MCE does not depend on temperature. Relationships between magnetothermal properties and structure of the complexes are analyzed. The conclusion is argumented that the reason of changes in magnetothermal properties after the replacement of axial ligand in gadolinium complexes and complexes of lanthanides with an unsymmetrically filled f-shell is non-planar geometry of the coordination site and specific electronic properties of the central ion. It is concluded that heat capacity of the complexes slightly increases with an increase in temperature and more noticeably in the case of (AcO)GdTPP; a magnetic component of heat capacity is revealed only in (AcO)GdTPP at temperatures above 298 K, which is connected perhaps with a temperature change in the crystal lattice of the complex and influence of the magnetic properties of gadolinium ion on this change.

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.

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.

Structural modification and kinetic stability of octaethylporphyne complexes with palladium (II)

The influence of gradual meso-phenyl substitution in 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyne (H2OEP) on the stability of its complexes with Pd(II) in comparison to the meso-tetraphenylporphyne complex with unsubstituted Cβ atoms is investigated by means of the chemical kinetics and physicochemical analysis. Using the spectral methods, the states and reactions of complexes in the AcOH-H2SO4 mixures is studied for the wide range of compositions. It is found that, the coordination centers are stable in mixtures with compositions of up to 100% of H2SO4. Whether in the molecular state or in association with a proton (PdOEP and its mono-meso-phenyl derivative), the complexes undergo transformations that are investigated by chemical kinetics. It is shown that instead of the usual dissociation of the coordination center, single-electron oxidation in the macrocycle of complexes takes place. A multistage mechanism is revealed that involves the kinetically significant equilibrium between the formation of H-associated complex and irreversible coordination of molecular oxygen, followed by the acid-assisted transfer of an electron from the aromatic system to this oxygen. The oxidation stability of complexes is determined, and the relation between the structure of macrocyclic ligand and the electronic structure of coordination center is discussed.

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.

Novel 2′-(pyridin-4-yl)-5′-(pyridin-2-yl)-1′-(pyridin-2-yl)methylpyrrolidinyl[60]fullerene-hydroxyoxo(5,10,15,20-tetraphenyl-21H,23H-porphynato) molybdenum(V) dyads

Interaction between hydroxyoxo(5,10,15,20-tetraphenylporphyrinato)molybdenum(V) and 2′-(pyridin-4-yl)-5′-(pyridin-2-yl)-1′-(pyridin-2-yl)methylpyrrolidinyl[60]fullerene in toluene has been studied by means of spectrophotometry. The reaction proceeds via two stages: rapidly established equilibrium between the reactants and their molecular complex 1: 1 [K = (1.97 ± 0.52) × 104 L/mol] followed by slow irreversible displacement of hydroxy group into the second coordination sphere to form cationic outer sphere complex (k = 0.26 L s−1 mol−1). The effect of fullerene fragment on pyridine fragments coordination has been considered.

Thiadiazoloporphyrinoids. Coordination of hexa(4-tert-butylphenyl)-substituted trithiadiazoltripyrrol macrocycle with Ni(II) in DMF

The rate constants, partial orders in the reagent concentrations and activation parameters of interaction of macroheterocyclic compound based on consecutively alternating fragments of thiazole and 3,4-bis(4-tert-butylphenyl)pyrole (3 + 3) with dehydrated Ni(OAc)2 in dry DNF depending on the reagent concentrations and temperature were determined. Within a narrow range of the salt concentrations ((1.58−1.87) × 10−4 mol/l), the third-order equation of the reaction rate was obtained i.e., the first order in a macrocyclic ligand and the second order in a salt, which was interpreted in terms of the mechanism of a stepwise coordination with three [Ni(OAc)]+ ions that is reversible only at the second step. Because of the low solubility of McH3, the monomer-dimer equilibrium also becomes kinetically significant. The constant of McH3 dimerization in DMF at 298 K equal to 1.6 × 105 mol−1 was determined by spectrophotometric titration.