Coordination of aza heterocycles with macroheterocyclic metal complexes in amphiprotic media: III. Kinetics and mechanism of inner-sphere ligand exchange in (tetraphenylporphyrinato)chromium(III)

Inner-sphere replacement of alcohols by imidazole and its derivatives in the complex (acetato)-(tetraphenylporphyrinato)chromium(III) was studied by electronic absorption spectroscopy. The rate constants and activation parameters of the process were calculated. The entering ligand structure was shown to affect the reaction rate, while the alcohol nature (departing ligand) does not influence the kinetic parameters of the process to an appreciable extent. Regression analysis revealed participation of imidazole and ethanol in the rate-determining stages. The kinetic equation for the inner-sphere axial substitution implies interaction of a free alcohol molecule with that coordinated to chromium, followed by replacement of the associate by the heteroring. Mathematical processing of the kinetic data in terms of the proposed solvolytic association-dissociation mechanism gave the rate constants for particular stages of the process and showed an extremal relation between the rate constant and composition of the solvent.     

Effect of pressure on the proton transfer rate from a photoacid to a solvent. 4. Photoacids in methanol

The pressure dependence of the excited-state proton dissociation rate constant of four photoacids, 2-naphthol-6,8-disulfonate (2N68DS), 10-hydroxycamptothecin (10-CPT), 5-cyano-2-naphthol (5CN2), and 5,8-dicyano-2-naphthol (DCN2), are studied in methanol. The results are compared with the results of the pressure dependence study we recently conducted for several photoacids in water, ethanol, and propanol. The pressure dependence is explained using an approximate stepwise two-coordinate proton transfer model. The increase in rate, as a function of pressure, manifests a strong dependence of proton tunneling on the distance which decreases with an increase of pressure between the two oxygen atoms involved in the process. The decrease in the proton transfer rate with increasing pressure reflects the dependence of the reaction on the solvent relaxation rate. We found that, for the relatively weak photoacids 2N68DS, 10-CPT, and 5CN2, the proton transfer rate constant increases by a factor of about 5-8 at a pressure of about 1.5 GPa. For a strong photoacid like DCN2, the rate increase was only by a factor of 2.     

Synthesis of tetraphenylporphins with active groups in the phenyl rings. 1. Preparation of tetrakis(4-aminophenyl)porphin

Condensation of p-nitrobenzaldehyde with pyrrole in propionic acid with added acetic anhydride gave tetrakis(4-nitrophenyl)porphin (24%), by the reduction of which tetrakis(4-aminophenyl)porphin, which was also obtained by hydrolysis of tetrakis(4-acetamidophenyl)porphin, was synthesized.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1354–1355, October, 1982.     

Thermodynamic parameters of sublimation of calix[4]arenes

The temperature dependences of the vapor pressure of calix[4]arenes were determined by the Knudsen effusion method. Some calix[4]arenes can form congruently subliming intramolecular compounds with a solvent. The thermodynamic parameters of the sublimation of the compounds were calculated. Molecules of organic solvents incorporated in the cavity of calix[4]arenes stabilize the crystal lattice, increasing the enthalpy of sublimation. The electrostatic interactions presumably make a significant contribution to stabilization of the crystal lattice of stoichiometric complexes of calix[4]arenes with solvents.     

Synthesizing of silver nanoparticles by thermal implantation of its ions in ED-20 epoxy oligomer

Stable silver particles of 39 nm in diameter were synthesized by the thermal implantation of its ions in ED-20 epoxy oligomer.     

The Condition of Metal Complexes of Tetraanthraquinoneporphyrazines in Solutions

Types of dimers of aluminum and cobalt complexes of tetraanthraquinoneporphyrazines were identified. Thermodynamic characteristics of dissociation of the dimers in aqueous media were obtained. The kinetics of the deactivation of the triplet state of the aluminum complexes of sulfonated phthalocyanine and tetraanthraquinoneporphyrazine was studied.

     

Structure and properties of (Ac)Fe(III)-5,15-diphenyl-3,7,13,17-tetramethyl-2,8,12,18-tetrabutylporphyrin in the reaction with organic peroxides in benzene: The effect of imidazole on reaction kinetics

The kinetics of the reaction between (Ac)Fe(III)-5,15-diphenyl-3,7,13,17-tetramethyl-2,8,12,18-tetrabutylporphyrin and dicumene peroxide in benzene at 295 K was studied with the purpose of further studying the effect of the conformational and electronic factors of nonplanar metalloporphyrinates on redox properties using a combination of computational and spectrophotometric methods. The molecular structures of reagents and intermediates of the studied reaction were optimized by the PM3 quantum-chemical method. The obtained characteristics were analyzed, and the distortion of a macrocycle was established to considerably increase in the reaction of iron(III) porphyrinate with peroxides. The intermediate molecule was found to be sterically hindered and extremely unstable. The kinetic characteristics of the reaction were obtained spectrophotometrically. The nature of a metal atom and the distortion of a macrocycle were established to have some effect on the process rate. The introduction of imidazole into a reaction mixture and the variation of concentration of a base were shown to produce some changes in the composition of reagents and the kinetics of the process. A good agreement between experimental and calculated data was observed.