АТРОПОИЗОМЕРИЯ 5,10,15,20-ТЕТРАКИС-(3-N-МЕТИЛПИРИДИЛ)-ПОРФИРИНА

The spectral properties of the 5,10,15,20-tetrakis-(3-N-methylpyridyl)-porphyrin were studied in the water solution and the temporal evolution of absorption spectra was revealed. The origin of the spectral changes was found to be due to the solution heterogeneity which is based on the coexistence of atropoisomers. These atropoisomers differ in their pyridyl groups, positioning relative to the mean plane of the tetrapyrrolic macrocycle due to an unrestricted rotation of substituents around the Сm–С1 bond. The observed spectral changes are shown to reflect the redistribution of the atropoisomer concentrations after establishing the equilibrium distribution that is over approximately within 300 hours after the preparation of a solution at a temperature of 290 ± 2 K. The atropoisomerization is suggested to be the inherent property of all 5,10,15,20-tetraarylporphyrins with an asymmetric substitution of aryl groups with respect to the axis passing through the Сm–С1 bond. The prospects for the practical applications of the revealed phenomenon are discussed. Исследованы спектральные характеристики 5,10,15,20-тетра-(3-N-метилпиридил)-порфирина в во- дном растворе и обнаружена временная эволюция спектров поглощения. Установлено, что причиной спектральной эволюции является гетерогенность раствора, обусловленная наличием нескольких атропоизомеров, различающихся положением пиридильных групп относительно средней плоскости тетрапиррольного макроцикла молекулы порфирина благодаря свободному вращению заместителей вокруг связи Сm–С1. Показано, что наблюдаемые спектральные превращения отражают перераспределение концентраций атропоизомеров в ходе установления равновесного распределения, которое завершается примерно через 300 ч после приготовления раствора при температуре 290 ± 2 К. Предложено, что явление атропоизомерии следует считать присущим всем 5,10,15,20-тетраарилпорфиринам с асимметричным относительно проходящей через связь Сm–С1 оси замещением арильных групп. Обсуждены возможности практического использования данного явления.

Modern Trends of Organic Chemistry in Russian Universities

© 2018, Pleiades Publishing, Ltd. This review is devoted to the scientific achievements of the departments of organic chemistry in higher schools of Russia within the past decade

Temperature dependent steric hindrance effects in triplet state relaxation of meso-phenyl-substituted Pd-octaethylporphyrins

The analysis of spectral-kinetic results of transient absorption and phosphorescence experiments has been carried out in a wide temperature range (80-293K) for a series of Pd-octaethylporphyrin derivatives (PdOEP) with increasing number of bulky meso-phenyl substituents. In order to elucidate the influence of steric hindrance interactions, as well as porphyrin macrocycle non-planarity on photophysical characteristics and relaxation pathways of triplet states, the following parameters were compared: i) T-state positions on the energy scale, ii) phosphorescence lifetimes and T1 -Tn transient absorption spectra, iii) phosphorescence quantum efficiencies, iv) activation energies of temperature-dependent phosphorescence rate constants for planar PdOEP and non-planar PdOEP-meso(Ph)n molecules

Temperature dependent steric hindrance effects in triplet state relaxation of meso-phenyl-substituted Pd-octaethylporphyrins

The analysis of spectral-kinetic results of transient absorption and phosphorescence experiments has been carried out in a wide temperature range (80-293K) for a series of Pd-octaethylporphyrin derivatives (PdOEP) with increasing number of bulky meso-phenyl substituents. In order to elucidate the influence of steric hindrance interactions, as well as porphyrin macrocycle non-planarity on photophysical characteristics and relaxation pathways of triplet states, the following parameters were compared: i) T-state positions on the energy scale, ii) phosphorescence lifetimes and T1 -Tn transient absorption spectra, iii) phosphorescence quantum efficiencies, iv) activation energies of temperature-dependent phosphorescence rate constants for planar PdOEP and non-planar PdOEP-meso(Ph)n molecules

Catalyzed M–C coupling reactions in the synthesis of s-(pyridylethynyl) dicarbonylcyclopentadienyliron complexes

The reactions between terminal ethynylpyridines, (trimethylsilyl)ethynylpyridines and cyclopentadienyliron dicarbonyl iodide were studied under Pd/Cu-catalyzed conditions to develop a synthetic approach to the σ-alkynyl iron complexes Cp(CO)(2)Fe–C[triple bond, length as m-dash]C–R (R = ortho-, meta-, para-pyridyl). Depending on the catalyst and reagents used, the yields of the desired σ-pyridylethynyl complexes varied from 40 to 95%. In some cases the reactions with ortho-ethynylpyridine gave as byproduct the unexpected binuclear FePd μ-pyridylvinylidene complex [Cp(CO)Fe{μ(2)-η(1)(C(α)):η(1)(C(α))-κ(1)(N)-C(α)[double bond, length as m-dash]C(β)(H)(o-C(5)H(4)N)}(μ-CO)PdI]. The conditions, catalysts, and reagents that provide the highest yields of the desired σ-pyridylethynyl iron compounds were determined. The methods developed allowed the synthesis of the corresponding σ-4-benzothiadiazolylethynyl complex Cp(CO)(2)Fe–C[triple bond, length as m-dash]C–(4-C(6)H(3)N(2)S) as well. Eventually, synthetic approaches to σ-alkynyl iron complexes of the type Cp(CO)(2)Fe–C[triple bond, length as m-dash]C–R (R = ortho-, meta-, para-pyridyl, 4-benzothiadiazol-2,1,3-yl) based on the Pd/Cu-catalyzed cross-coupling reactions were elaborated

Molecular Structure of Nickel Octamethylporphyrin—Rare Experimental Evidence of a Ruffling Effect in Gas Phase

The structure of a free nickel (II) octamethylporphyrin (NiOMP) molecule was determined for the first time through a combined gas-phase electron diffraction (GED) and mass spectrometry (MS) experiment, as well as through quantum chemical (QC) calculations. Density functional theory (DFT) calculations do not provide an unambiguous answer about the planarity or non-planar distortion of the NiOMP skeleton. The GED refinement in such cases is non-trivial. Several approaches to the inverse problem solution were used. The obtained results allow us to argue that the ruffling effect is manifested in the NiOMP molecule. The minimal critical distance between the central atom of the metal and nitrogen atoms of the coordination cavity that provokes ruffling distortion in metal porphyrins is about 1.96 Å