Том 67, № 3 (2018)

Over the past decades, the pincer ligands have attracted an increasing interest due to the unique properties of the coordination compounds they form. These monoanionic tridentate ligands are of great importance in organometallic and coordination chemistry. Their complexes with transition metals are used as homogeneous catalysts for various processes and also as functional materials with specified properties. The metal complexes formed by the pincer ligands provide an efficient alternative to the existing catalysts based on noble metals and, hence, the use of these complexes is a promising task of the modern chemical science. Therefore, nickel as the most accessible and inexpensive analog of palladium and platinum is of great practical interest. In this review, we consider the diversity of nickel complexes with pincer ligands, as well as the existing methods for their preparation and practical application.

The mechanisms of the hydrogenation of phenylacetylene and styrene to ethylbenzene on the Pd{111} surface, which are secondary reactions of the selective hydrogenation of phenylacetylene, were studied by the DFT-PBE method. The position of the Ph group of the styrene molecule with respect to the Pd surface is shown to exert a noticeable effect on the mechanism of the process. If the Ph group is adsorbed on the Pd surface, then the addition of the first H atom to the terminal C atom of the styrene molecule is most probable. If Ph does not contact the surface, then the most substituted C atom of the styrene molecule is first hydrogenated. On the whole, the interaction of the Ph group with the Pd{111} surface results in stable adsorption structures, the hydrogenation of which on the Pd{111} surface is strongly hindered. The Gibbs activation energy (ΔG^≠₂₉₈) is 22.9 and 27.1 kcal mol^–1 in the most probable reaction routes of styrene hydrogenation to ethylbenzene and direct hydrogenation of phenylacetylene to ethylbenzene, respectively.

In the interaction of cyclohexa-1,4-diene (1,4-CHD) with a mixture of biphenyl and metallic lithium or sodium in THF at 20 °C, three processes occur, viz., disproportionation of 1,4-CHD to form benzene and cyclohexene, dehydrogenation of 1,4-CHD to form benzene and molecular hydrogen, and dehydrogenation of 1,4-CHD to form benzene and lithium or sodium hydride. In the case of lithium on the use of an equimolar amount of biphenyl, the isomerization of 1,4-CHD to cyclohexa-1,3-diene is also observed. When the molar ratio Li(Na): Ph₂ increases from 1 : 1 to 2 : 1, i.e., when the reaction is carried out in the presence of an alkali metal solid phase, the overall conversion of 1,4-CHD into benzene and cyclohexene increases. The use of mixtures of lithium and sodium leads to acceleration of the processes of the formation of benzene and cyclohexene. The possible mechanism of the synergistic effect found is discussed.

New bis(amidinate) complexes of calcium, [2,6-Prⁱ₂C₆H₃NC(But)NC₆H₄OMe-2]₂Ca(DME) (2), and divalent ytterbium, [2,6-Prⁱ₂C₆H₃NC(But)NC₆H₄OMe-2]₂Yb (4), were synthesized by the transamination of the bis(amide) derivatives [(Me₃Si)₂N]₂M(THF)₂ (M = Ca, Yb) with two equivalents of amidine 2,6-Prⁱ₂C₆H₃N=C(But)N(H)C₆H₄OMe-2, in which one nitrogen atom bears an o-methoxyphenylene moiety capable of coordinating a metalion. An X-ray diffraction study showed that, despite very similar ionic radii of Ca²⁺ and Yb²⁺, the amidinate ligands in complexes 2 and 4 bind to these ions in different coordination modes. In the calcium complex, both ligands adopt a κ²-N, O-chelating coordination mode. In the divalent ytterbium compound, one ligand is chelating and binds to the metalion in a κ²-N, O-coordination mode, while the second ligand is coordinated via both the N and O (κ²) atoms and the arene ring of the 2,6-Prⁱ₂C₆H₃ moiety (η⁶-coordination mode).

New heterogenizated catalysts for the allylation of norbornadiene (NBD) were prepared by the adsorption immobilization and surface assembly methods. The obtained catalysts were screened in the allylation of NBD, and the main technological parameters of the process were determined.

Aluminum carbenoid Et₂AlCH₂I reacts with 6-substituted fulvenes to give tricyclopropanes in high yields. Calculations at the B3LYP/6-31G(d) level of theory show that coplanar arrangement of the double bonds facilitates cyclopropanation due to conjugation in the transition state. Aluminum carbenoid Et₂AlCH₂I was generated by either the reaction of equimolar amounts of Et₃Al and CH₂I₂ in hexane or treatment of Et₂AlI with CH₂N₂ in dichloromethane.

Three new metal-organic coordination polymers were obtained namely, [Mn₃(chdc)₃-(NMP)₂(DMF)₂] (1, chdc^2– is trans-1,4-cyclohexanedicarboxylate, NMP is N-methylpyrrolidone, DMF is N,N-dimethylformamide), [Zn₃(chdc)₃(NMP)₂]•2NMP (2), and [Zn₃(chdc)₃(ur)-(DMF)_0.5]•DMF (3, ur is the urotropine). The crystal structures of polymers 1, 2, and 3 were determined by single-crystal X-ray crystallography. All three compounds were found to contain a trinuclear secondary building unit {M₃(OOC)₆}. Coordination polymers 1 and 2 have a layered structure, while polymer 3 has a three-dimensional coordination framework with isolated pores formed due to the presence of urotropine bridging molecules. Compounds 1 and 3 were characterized by IR spectroscopy, thermogravimetric and elemental analysis data, powder X-ray diffraction. Compound 3 was also characterized by UV-Vis diffuse reflectance spectrum.

Lithiation of 1-bromomethyl-o-carborane with lithium diisopropylamide (LDA) in THF results in the in situ formation of 1-lithio-2-bromomethyl-o-carborane, the reaction of which with 3-trimethylsilylprop-2-ynal gives 2-(2-trimethylsilylethynyl)-3,4-(о-carborano)-2,5-dihydrofuran. Subsequent base-catalyzed desilylation furnishes new terminal alkynes of closoand nido-carborane series.

The one-pot process of anodic transformation of N-alkyl-3-aminopyrazoles into azopyrazoles under conditions of membraneless electrolysis in an aqueous solution of NaBr was studied for the first time. It was found that under these conditions the aminopyrazoles, which do not have a substituent at position 4, transform into the corresponding 4,4´-dibromoazopyrazoles. The corresponding yield was in the interval of 28—80%, depending on the structure of the products. The transformation of 4-substituted aminopyrazoles resulted in the formation of azopyrazoles in the yields lying within 62—86% when this process was implemented under conditions with the anodically generated Br₂ acting as a mediator. A convenient method of anodic synthesis of azopyrazoles in an aqueous medium without the use of additives of chemical oxidants was proposed. The process is environmentally sound and is characterized by a high atom efficiency (>85%).

A reaction of dimethyl bicyclo[2.2.2]oct-5-ene-endo-2,endo-3-dicarboxylate with 1,3-benzо- thiazole-2- and 3-methoxycarbonylpyridine-2-sulfenyl chlorides leads to two types of heterocyclization products, which are formed through the ring closure by the oxygen atom of the carbоmethoxy group and/or by the nitrogen atom of the hetaryl fragment of the sulfenylating agent. The product ratio is affected by the medium nature and structural features of sulfenyl chlorides.

The possibility of covalent fixing of hydroxyl-containing photochromic compounds on the surface of polyurethane films containing excess isocyanate groups was studied. By comparing the spectral-kinetic characteristics of polyurethane films treated with solutions and films with chromene or spirooxazine derivatives introduced into the bulk polymer, it was concluded that in the first case the polymer swells and the photochromic compound becomes distributed predominantly in the bulk polymer rather than on the surface.

The new amide conjugates were synthesized from methyl pheophorbide a and its carboxyl derivatives by reactions with aminomethyl derivatives of 2,4-dimethylphenol, 2-isocamphyl-4- methylphenol, 2-bornyl-4-methylphenol, and 2-isobornyl-4-methylphenol. The antioxidant activity of some conjugates was established by investigation of their ability to inhibit the accumulation of secondary products of lipid peroxidation in a brain of laboratory mice in vitro. The neuroprotective properties of porphyrin and terpenylphenol conjugates have been studied on the model of H₂O₂-induced oxidative stress in SH-SY5Y cells (neuroblastoma).

Regioselective synthesis of new dispiro indolinones combining both an indolinone and an oxazolone fragment in their structure comprised the 1,3-dipolar cycloaddition of azomethine ylides, generated in situ from isatin and sarcosine, at 2-aryl-5-arylmethylidene-substituted 1,3-oxazol-5(4H)-ones. When ortho and para halogen atoms were present in the aromatic substituents of the starting oxazolones, complex mixtures containing large amounts of oxazoline ring opening products and their dispiro derivatives were formed. The cytotoxicity of compounds was tested by MTT on LNCaP, PC3, HCT116, MCF7, A549, HEK, and VA13 cell lines. The compound possessing the best cytotoxicity revealed the IC₅₀ = 1.08±0.96 μM towards the p53- expressing LNCaP cells and lower activity (IC50 = 3.21±1.45 μM) towards the non-expressing p53 protein PC3 cells, however, it has proved inactive towards the HCT cells, both expressing (HCТ+/+) and non-expressing (HCT–/–) p53.

A synthetic route to 1-hydroxy- and 1-alkoxymethyl-3-polyfluoroalkylpyrazoles via regioselective N-hydroxy- and alkoxymethylation of N-unsubstituted pyrazoles with paraformaldehyde has been proposed. The alkoxyalkylation of polyfluoroalkylpyrazoles proceeds in aqueous-alcohol medium, whereas hydroxymethylation requires anhydrous conditions.

A reaction of Bu₄N[8,8´-(MeS)₂-3,3´-Co(1,2-C₂B₉H₁₀)₂] with (MeCN)₃W(CO)₃ in dichloromethane gave a mixture of Bu₄N{(CO)₅W[κ-8,8´-(MeS)₂-3,3´-Co(1,2-C₂B₉H₁₀)₂]} and Bu4N{[(CO)₅W]₂[κ²-8,8´-(MeS)₂-3,3´-Co(1,2-C₂B₉H₁₀)₂]}, which were separated by column chromatography on silica gel.