The work is aimed at solving the problem of neutralization of persistent organic pollutants by catalytic methods. In order to identify the relationship between electronic and steric factors of carbenes with catalytic efficiency in the reaction of hydrodehalogenation of haloarenes, the parameters for estimating the ligand influences are proposed (electronic - Ie indices, Ph philicities, ED electron donicities, and EA electron acceptabilities, steric - dimerization energies) using theoretical methods (DFT, B3LYP5, RHF). Synthesis of new heteroaromatic carbenes of the series of sterically shielded 1,3-diarylphenanthro-[9,10-d]imidazol-2-ylidene, 1,3-diaryl-2-methy­lene­phenan­thro-[9,10-d]imidazoline, tetrahydropyrimidin-2-ylidene, 1,3-diaryl­imidazol-2-ylidene, 1,3,4-triaryl-1,2,4-triazol-5-ylidenes, their carbene complexes with palladium iodide, as well as the carbene complex of the superbasic anionic carbene 1,3-bis-(4-oxidophenyl)-imidazol-2-ylidene with nickel(II) ion. 1H and 13C NMR spectroscopy, mass spectrometry and X-ray diffraction study methods were used to establish the structures of the synthesized compounds. A high catalytic effect of a number of sterically shielded carbene complexes (2.4b, 3.5, 4.6a) in the reaction of hydrodehalogenation of p-dichlorobenzene haloarenes with sodium methoxide in isopropanol at 80 °С (TON 98000–110000) was revealed that can be applied to solve the problem of neutralization of persistent organic pollutants. The efficiency of catalysis by sterically open compounds 4.6b and 6.7 appeared to be low (TON 74, 128). The high catalytic effect of sterically shielded compounds is explained by the increased stability of the complexes under the conditions of an alkaline medium caused by metal alkoxides.

A series of new stable halogenated carbenes, 1-tert-butyl-3,4-diaryl-1,2,4-triazol-5-ylidenes, has been synthesized. According to quantum chemical calculations, 4-(2,3,4-trifluorophenyl)-substituted 1-tert-butyl-3,4-diaryl-1,2,4-triazol-5-ylidene is the least basic in comparison with the known sterically open stable heteroaromatic carbenes. Upon heating in organic solvents these carbenes undergo a tandem induced reaction thereby forming 5-amidino-1,2,4-triazoles. The interaction of carbenes with benzylidenemalononitrile, propanesultone and phenyl isothiocyanate results in zwitterionic compounds of the 1,2,4-triazole series. The data for X-ray diffraction study of 1-tert-butyl-3-phenyl-4-(2,4-difluorophenyl)-1,2,4-triazol-5-ylidene, its protonated salt, complex with copper(i) iodide, related complex of 1-tert-butyl-3-phenyl-4-(2-trifluoromethylphenyl)-1,2,4-triazol-5-ylidene, and adduct of 1-tert-butyl-3-phenyl-4-(4-bromophenyl)-1,2,4-triazol-5-ylidene and propansultone are given.

The book presents the main methods of synthesis used today to obtain organic matter. For students of chemical specialties of universities, as well as graduate students, teachers and researchers.

The electronic properties of carbenes including thermodynamic parameters such as new electronic philicity indices Ie, Ph, and for comparizon chemical hardnesses η, proton affinities (РA) calculated by DFT method (B3LYP5/6-31G*/RHF for definition of electronic indices and B3LYP5/3-21G/RHF, B3LYP5/3-21G/UHF for definition of chemical hard¬nesses) have been discussed in the paper. With their help, the estimation of philicities, electron-donating and electron-withdrawing abilities of a wide range of carbenes of both nucleophilic and electrophilic type was carried out. It was established that the philicities of carbenes according to electronic indices Іе, Ph depend on the carbenic structure (the backbone of the molecule and steric effects of substituents) and also on the reagent structure, particularly its steric effect. For typical nucleophilic carbenes, the Ph is in the range of 1–3,0, for neutral carbenes 1–1,5, IeH 8,5–22,2 eV, for neutral carbenes IeH 8,5–10,5, for typical electrophilic – in the intervals of PhH –0,3–0,5, IeH –3,4–3,4 eV. The intermediate values (Ph 0,5–1,0, IeH 3,4–8,5 eV) are characteristic for typical ambiphilic carbenes. In the evaluation of electron-donating and electron-withdrawing properties, the values of ED and EA should be taken into account (maximal EDH values were found for neutral carbene 20 (13,8 eV) and for superbasic anionic carbenes (for 22 18,4 eV)). The highest electron acceptability EAH was found for cationic carbene 29 (11,8 eV). In the reactions with carbon ions, the values of the IeH, PhH indices decrease significantly, and the electron acceptability increases. Increasing the steric effects leads to «inversion» of philicities for nucleophilic carbenes (Ph up to 0,1), and the properties of electrophilic carbenes become even more pronounced (Ph up to –2,7). The found dependences of the electronic properties of carbenes allow regulating the structure of carbenes to achieve certain characteristics, which together with stability factors can be used in the design of structures for synthesis and practical application.

Carbenes are known to be highly reactive compounds, which can, in turn, spontaneously transform to dimers and products of rearrangements. Therefore, the question about the estimation of stability of carbenes is fundamental in the design of compounds for their subsequent synthesis and application. Aim. To consider the known methods for assessing the stability and stabilization of carbenes, first of all, created by the authors of the article, and show their possibilities in predicting the properties of carbenes. Materials and methods. The study was performed using the DFT method (B3LYP5, 6-311G**, RHF) to estimate the stabilization energies, and the DFT (B3LYP5, 6-31G, RHF) to obtain dimerization energies. Results and discussion. The ways of solving the problem of stability of carbenes by the methods of quantum chemistry are discussed, in particular the application of new criteria for the stabilization of cyclic compounds – energies of the general and cyclic stabilization, energies of non-aromatic conjugations. To assess the possibility of isolating compounds the study of standard dimerization enthalpies (according to the ESP electronic and steric parameter proposed) for different classes of heterocyclic carbenes has been performed taking into account conformational factors. The scale of substituent effects on the stability of carbenes has been developed. It has been shown that sterically shielding substituents cause not only the kinetic stabilization, but also the thermodynamic one. The skeletons of the molecules have been estimated for their degree of influence on the stability of the compounds. Conclusions. The parameters proposed for assessing the energies of the total and cyclic stabilization of carbenes, the dimerization energies of complex carbenes (electronic and steric parameter) allow identifying the most stable structures in the design of compounds for their subsequent synthesis and application.

For carbenes as ambiphilic compounds there is no single scale for estimating their electron properties. Aim. To consider the known methods of estimating the electron-donating and electron-withdrawing properties of carbenes, first of all, created by the authors of the article, and show their possibilities in predicting the properties of carbenes. Materials and methods. The studies were performed using the DFT (B3LYP5/6-311G/RHF) method to estimate proton affinity, DFT (B3LYP5/3-21G/RHF and B3LYP5/3-21G/UHF) to determine chemical hardness and electronic indices. Results and discussion. The electronic properties of carbenes, including thermodynamic parameters, such as proton affinity (PA), chemical hardness η, and new electronic indices Ie, are discussed in the paper. With their help, the electron-donating and electron-withdrawing ability of a wide range of carbenes of both nucleophilic and electrophilic type has been estimated. It has been shown quantitatively that the electronic properties of carbenes depend both on the backbone of the molecule (for example, the type of the heterocyclic nucleus) and on substituents. The above data show the ways of regulating the structure of carbenes to achieve certain characteristics, which together with stability factors can be used in the design of structures for the synthesis and practical application. Conclusions. The author’s results of estimating proton affinity, chemical hardness and electronic indices for the design and use of carbene compounds are considered. Electronic indices have been shown to have some advantages over others for determining the nature (electron-donating and electron-withdrawing) of carbenes.

РЕДАКЦІЙНА КОЛЕГІЯ Б. Д. Грищук -доктор хімічних наук, професор (головний редактор) Я. Г. Бальон -доктор хімічних наук, професор В. С. Броварець -доктор хімічних наук, професор М. В. Вовк -доктор хімічних наук, професор М. І. Короткіх -доктор хімічних наук, професор О. С. Лявинець -доктор хімічних наук, професор В. П. Новіков -доктор хімічних наук, професор М. Д. Обушак -доктор хімічних наук, професор В. І. Станінець -доктор хімічних наук, професор О. П. Швайка -доктор хімічних наук, професор В. С. Барановський -кандидат хімічних наук, доцент

РЕДАКЦІЙНА КОЛЕГІЯ Б. Д. Грищук -доктор хімічних наук, професор (головний редактор) Я. Г. Бальон -доктор хімічних наук, професор В. С. Броварець -доктор хімічних наук, професор М. В. Вовк -доктор хімічних наук, професор М. І. Короткіх -доктор хімічних наук, професор О. С. Лявинець -доктор хімічних наук, професор В. П. Новіков -доктор хімічних наук, професор М. Д. Обушак -доктор хімічних наук, професор В. І. Станінець -доктор хімічних наук, професор О. П. Швайка -доктор хімічних наук, професор В. С. Барановський -кандидат хімічних наук, доцент

The 1-adamantyl substituted stable carbene 5 and the biscarbene 9 of the 1,2,4-triazole series with sterically shielding groups at the position 4 of the heterocyclic ring (dbmp, dipp) have been synthesized in three steps starting from the derivatives of 1,3,4-oxadiazole 1,6. A new method for the preparation of 1,3,4-triaryl-1,2,4-triazol-5-ylidenes (14a-c) has also been proposed and includes the Vilsmeier reaction of 2-benzoyl-1-formylphenylhydrazine with phosphorus chloroxide and aromatic amines, followed by deprotonation of the obtained 1,3,4-triaryl-1,2,4-triazolium salts. The method allows introduction of steric shielding substituents to the 4-position of the heterocycle. The resulting carbenes show promise as nucleophilic catalysts and ligands for carbene complex catalysts of organic reactions.

The present review deals with the syntheses and properties of individual heteroaromatic carbenes of the imidazole, 1,2,4and 1,2,3-triazole series, their fused analogs and mesoionic carbenes including unprecedented structures such as hyperbasic and hypernucleophilic carbenes. Particular emphasis is placed on their physical properties, novel chemical transformations, and catalytic properties.

Highly efficient carbene and polycarbene catalysis of the transesterification reaction of ethyl benzoate in methanol has been observed and results in values of TON as high as 4000 – 6150 at a molar ratio of ester to methanol of 1:18 at room temperature. The most effective catalysts were found to be the individual carbenes or in situ generated carbenes, namely adamantyl and aromatic substituted cyclic compounds and polymeric carbenes. None of the reactions requires the use of molecular sieves. The polymeric imidazol-2-ylidene catalyst was used for the efficient production of biodiesel fuel from sunflower oil.

A series of [1,3]thiazino[3,2-a]benzimidazolium salts modified in the benzene ring by a condensed 1,4-dioxane ring has been prepared. Reaction with epichlorohydrin occurs with recyclization to form derivatives of 3-(2,3-epithiopropyl)benzimidazol-2-one.

The new sterically shielded 1,3,4-trisubstituted 1,2,4-triazol-5-ylidenes 8b–d were synthesized by a three step method starting from 2-phenyl-1,3,4-oxadiazole. The syntheses of palladium complexes 9a–d and 10a–d (including the sterically shielded derivatives 9c,d and 10a–d) were carried out via the reactions of the stable carbenes 8a–d with palladium halogenide salts in THF or toluene solution. Complexes 9c,d and 10a–d were found to be excellent catalysts for the reductive dechlorination (hydrodechlorination) of p-dichlorobenzene. The structures of 8c, 9a,b, and 10a were determined by single-crystal X-ray diffraction.

A new sterically shielded carbene with branched aromatic substituents (9a) and two palladium halogenide complexes (11a,b) have been prepared. The single crystal X-ray structures of free carbene 9a and palladium carbene complexes 10b and 11a were determined. Very high catalytic efficiencies were evident for the sterically shielded palladium carbene complexes 10b and 11a,b when the latter complexes were employed as catalysts for hydrodechlorination of the chloroarenes p-dichlorobenzene and hexachlorobenzene. When optimized, the foregoing approach is significantly more effective than those of currently known transition metal carbene complexes. The most active catalysts were found to be the monocarbene complexes of palladium chloride and iodide, both of which feature highly branched aromatic substituents (11a,b).

In this review, the issues concerning the effectiveness of catalysis by carbenes and their transition metal complexes in a range of organic reactions are discussed as one of the developing areas in contemporary organic chemistry. Among the transformations catalyzed by carbenes, our attention was directed to the transesterification and benzoin condensation reactions that are potentially important for practical application. In the case of transformations catalyzed by the metal carbene complexes, we focussed on the reduction of multiple bonds and the reductive dehalogenation of haloaromatic compounds that are important for organic synthesis and utilization of environmental toxicants.

A novel 1,3-dimethyl-1,3-di-(1-adamantyl)formamidinium perchlorate has been prepared via the Vilsmeier-Haack reaction of N-methyl-N-(1-adamantyl)formamide and N-methyl- N-(1-adamantyl)amine in a mixture of phosphorus oxychloride and benzene. The new formamidinium salt was found to undergo addition-elimination reactions when treated with sodium hydride in acetonitrile or propionitrile solution, thereby forming the corresponding �-(methyl(1-adamantyl)amino)acrylonitriles and N-methyl-N-(1-adamantyl)amine. The 1 H and 13 C NMR spectra and the single-crystal X-ray structure of the new formamidinium salt have been determined along with those of the related compound 1,3-di-(1-adamantyl)-1- cyanoamidine and the corresponding �-(dialkylamino)acrylonitriles.

Carbene complexes of nickel, palladium, and copper(I) effectively catalyze the reduction of aromatic ketones under the influence of 2-propanol in the presence of potassium hydroxide. Bis(1,3-dimethylbenzimidazol-2-ylidene)copper(I) iodide and the polymeric complex of crown-biscarbene with copper(I) iodide show the highest catalytic efficiency.

The results of investigations into the formation of the various ionic forms of heteroarenium salts, their characteristics, and their reactivity are summarized. Salts containing (4n+2)π-electron aromatic cations (n = 0–3), including chalcogenopyrylium (O, S, Se), azinium, benzo- and dibenzoazinium, and chalcogenoazolium (O, S, Se, NR) ions are examined. In this system of compounds the relationships between the structure and the macroscopic characteristics of the heteroarenium salts (ionization constants, association/dissociation constants, distances of closest interionic approach) and the effect of the nature of the ionic forms in the solutions on their reactivity in heterolytic reactions are analyzed.