N. G. Bichan

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.

Cobalt(II) porphyrin axially coordinated with 2′-(pyridin-4-yl)-5′-(pyridin-2-yl)-1′-(pyridin-2-ylmethyl)-2′,4′-dihydro-1′H-pyrrolo[3′,4′ : 1,2](C60-Ih)[5,6]fullerene: formation, chemical structure, and spectroscopic properties

Abstract Construction of new effective photovoltaic devices based on organic dyes has important implications for modern and future technologies. In this article, we studied the equilibrium, the rate, and the spectral manifestation of the reaction of [(2,3,7,8,12,18-hexamethyl,13,17-diethyl,5-(2-pyridyl)porphyrinato)cobalt(II)]–[2′-(pyridin-4-yl)-5′-(pyridin-2-yl)-1′-(pyridin-2-ylmethyl)-2′,4′-dihydro-1′H-pyrrolo[3′,4′ : 1,2](C60-Ih)[5,6]fullerene] triad formation as well as its spectral properties and photo electrochemical behavior. The cobalt porphyrin–pyridyl-substituted fullerene mixtures in toluene are self-assembling systems due to axial donor–acceptor binding between Co of the porphyrin complex and N-pyridyl of the substituted fullerene. The formation rate constant, k298K, and the stability constant, K298K, of donor–acceptor triad formed by coordination of two substituted fullerene molecules to Co porphyrin are (44.4 ± 0.8) mol L−1 s−1 and (56 ± 16)×107 L2 mol−2, respectively. Modification of the titanium electrode coated with the natural oxide film was carried out using the porphyrin–fullerene triad and its individual components. Photopotential and photocurrent density of the system with modified electrode were studied. The obtained results are of interest for creating porphyrin-based donor–acceptor systems as components in organic photovoltaics.

Synthesis and properties of a new (octaethylporphyrinato)-manganese(III)–pyridinyl-substituted pyrrolidinofullerene dyad

The formation of a porphyrin–fullerene dyad from 2′-(pyridin-4-yl)-5′-(pyridin-2-yl)-1′-(pyridin-3-ylmethyl)-2′,5′-dihydro-1′H-pyrrolo[3′,4′: 1,9](C60-Ih)[5,6]fullerene and (2,3,7,8,12,13,17,18-octaethylporphyrinato) manganese(III) with axial chloride ligand has been studied on a quantitative level with the goal of obtaining supramolecules possessing biological activity. Preliminarily, the reaction of manganese(III) porphyrin with pyridine has been studied. The donor–acceptor dyads are formed either instantaneously and reversibly (pyridine) or slowly and irreversibly (substituted fullerene). In both cases, the reaction is a one-step process for which thermodynamic and kinetic parameters have been determined. The results can be used to optimize conditions for the synthesis of porphyrin–fullerene dyads. The obtained dyads have been characterized by spectral data and stability constants.

Kinetics of the single-electron chemical oxidation of rhenium(V) meso -phenyl-β-octaethylporphyrinate

The states and reactions of rhenium(V) complexes with meso-monophenyl-β-octaethylporphines containing Cl− and OPh− as axial ligands O=Re(Cl)MPOEP and O=Re(OPh)MPOEP in concentrated sulfuric acid at 298–348 K are studied via spectral and kinetic methods. While stable along M-N bonds, O=Re(Cl)MPOEP is found to undergo slow oxidation after transforming into axial hydrosulfate complex O=Re(HSO4)MPOEP. It is shown that the sole electron oxidizing agent is atmospheric oxygen (with the assistance of highly concentrated protons) and the sites of reduction are aromatic ligands. The reaction product was identified as π-radical cation O=Re(HSO4)MPOEP·+. Forward and inverse chemical kinetics solutions are used to obtain a full kinetic equation and the reaction rate parameters of elementary steps, and to establish the stoichiometric mechanism of the composite oxidation of the complex. Complex O=Re(OPh)MPOEP in the form O=Re(OPh)(O2)MPOEP with coordinated oxygen is shown experimentally to be stable with respect to oxidation. The obtained results are important for identifying intermediates in processes catalyzed by stable metal porphyrins.

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-Ih)[5,6]fullerene} have been synthesized, and their principal properties (spectral parameters and reactivity toward fullerene-containing base) have been studied.

Use of chemical kinetics for the description of metal porphyrin reactivity

The results of use of chemical kinetics receptions, approaches and methods for the study of porphyrins and their metal complexes reactivity are discussed on an example of oxidation, acid-basic, and catalytic reactions of rhodium, palladium, and rhenium complexes of porphyrin in liquid solutions. The peculiarity of the porphyrin reaction rates is analyzed in a brief context of general provisions of the chemical kinetics. The opportunity to use the quasistationarity principle at the definition of the kinetic equation of the reactions with participation of metal porphyrins is shown. The transition from the process kinetic description to consideration of its mechanism is explored.

Properties of chemically generated π-radical cations and molecules of (meso-phenyl-β-octaethylporphyrinato)rhenium(V) with axial molecular oxygen

The state of existence and reactions of stable rhenium(V) complexes with β-octaethylporphin (O=Re(OPh)OEP, O=Re(Cl)OEP) and its meso-diphenyl-substituted derivatives (O=Re(Cl)5,15DPOEP) in concentrated H2SO4 at 318–348 K were studied. It was found that O=Re(Cl)5,15DPOEP undergoes slow single-electron oxidation at the aromatic ligand to give π-radical cation. The oxidation is accompanied by replacement of the axial Cl− ligand by the hydrogen sulfate ion present in excess. Full kinetic description of the intricate oxidation reaction of the complex involving atmospheric oxygen was obtained and parameters of simple reactions that constitute the intricate process were determined. In the case of O=Re(Cl)OEP and O=Re(OPh)OEP, the reaction stops after the formation of the cationic complex with axially coordinated oxygen and outer-sphere chloride ion O=Re(O2)OEP+ Cl−. The effect of the nature of axial and macrocyclic ligands in rhenium(V) porphyrins on the processes in sulfuric acid solutions of these compounds was established.

Formation Reaction and Chemical Structure of a Novel Supramolecular Triad Based on Cobalt(II) 5,10,15,20-(Tetra-4-Tert-Butylphenyl)-21Н,23Н-Porphyrin and 1-Methyl-2-(Pyridin-4′-Yl)- 3,4-Fullero[60]Pyrrolidine

Results of chemical kinetic/thermodynamic and spectroscopic studies of the reaction of cobalt(II) 5,10,15,20-(tetra-4-tert-butylphenyl)-21Н,23Н-porphyrin (CoIITBPP) with 1-methyl-2-(pyridin-4′-yl)-3,4- fullero[60]pyrrolidine (PyF) in toluene at 298 K, ending by the formation of donor-acceptor triad (PyF)2CoIITBPP, are presented. Kinetic and thermodynamic parameters of the two-way formation reaction of the triad are obtained. The chemical structure of the obtained porphyrin-fullerene triad is identified by UV, visible, fluorescent, IR, and 1H NMR spectroscopic techniques. The results are relevant for the problems of searching for supramolecular systems capable of photoinduced charge separation.

Chemical structure and reactions of axially coordinated iridium(III) porphyrins

Effect of modification of the axial (fifth and sixth) coordination sites on the physicochemical properties and reactivity of iridium(III) complexes with 5,10,15,20-tetraphenyl-21H,23H-porphine was studied. Oxidation reactions of (Cl)(H2O)IrTPP in protic solvents by atmospheric oxygen (on assistance of protons at high concentration) preceded by ligand substitution at the axial position were studied. It was found that (Cl)(H2O)IrTPP in 100% AcOH undergoes slow one-electron oxidation at the aromatic ligand to form π cation radical (CH3COO)(CH3COOH)IrTPP·+. The reaction was studied in 100% AcOH (H2O content 0.078%) at 288–308 K, its kinetic parameters were obtained. The (Cl)(H2O)IrTPP reaction product in CF3COOH was identified as complex (CF3COO)2IrIVTPP oxidized at the central metal cation. It was experimentally confirmed that the reaction in 99% CF3COOH at 298 K proceeds in two stages: the substitution of axial Cl− and H2O by excess CF3COO− (keff = (1.8 ± 0.1) × 10−3 s−1) and the oxidation of iridium to Ir(IV) (keff = (8.0 ± 0.5) × 10−5 s−1). Data on similar Re(III) complexes (PhO)ReTPP and (Cl)ReTPP are presented for comparison.