Vol 66, No 2 (2017)

The review summarizes literature data on the synthesis, crystal growth conditions, structures, and physicochemical properties of alkaline-earth and rare-earth element borates. The compounds under consideration were shown to be promising for the use as materials for electronics, laser and luminescent matrices.

Based on the method of random field distribution functions in Ising magnets, for the first time a theoretical description of thermal transitions in Jahn—Teller exchange clusters is suggested, which takes into account the interactions of polymeric chains in "breathing" crystal compounds. It was shown that the inclusion of this interaction can lead to both an intensification of spin-crossover type cooperative transitions in exchange clusters and their deceleration. The approach in question is generalized to include non-Jahn—Teller metal impurities in "breathing" crystals, which suppress cooperative effects in thermal transitions of Jahn—Teller exchange clusters. The obtained results qualitatively reproduce the temperature dependencies of magnetic properties of solid solutions Cu_1—xNi_x(hfac)₂L^R (hfac is hexafluoroacetylacetonate anion, ligand L^R is nitronyl nitroxide radical with pyrazole substituent at the second position of the imidazoline ring) when R = Et.

We synthesized 1-ethylimidazolyl-substituted nitronyl nitroxides, i.e., 2-(1-ethylimidazol-4-yl)- (L^4Et) and 2-(1-ethylimidazol-5-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole 3-oxide-1-oxyl (L^5Et). The stable radical L^5Et is an ethyl analog of 2-(1-methylimidazol-5-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole 3-oxide-1-oxyl (L^5Me) described earlier, the reaction of which with Cu(hfac)₂ (hfac is 1,1,1,5,5,5-hexafluoropentane-2,4-dionate) leads to the formation of the [Cu(hfac)₂(L^5Me)₂] jumping crystals. The reaction of Cu(hfac)₂ with L^5Et with reagent ratios 1: 2 and 1: 1 yields heterospin complexes [Cu(hfac)₂(L^5Et)₂] and [Cu(hfac)₂L^5Et]₂, respectively. X-ray diffraction study of the mononuclear complex [Cu(hfac)₂(L^5Et)₂] determined that the compound has a packing similar to that of jumping crystals studied earlier, with the only difference being that the O...O contacts between neigh- boring nitroxide groups were found to be 0.3—0.5 Å longer than in [Cu(hfac)₂(L^5Me)₂]. As a result of the lengthening of these contacts, [Cu(hfac)₂(L^5Et)₂] crystals lack chemomechanical activi- ty. We found that when cooling crystals of binuclear complex [Cu(hfac)₂L^5Et]₂ below 50 K, the antiferromagnetic exchange between unpaired electrons of the >N—•O groups of neighboring molecules leads to the full spin-pairing of the nitroxides, with only the Cu²⁺ ions contributing to the residual paramagnetism of the compound.

X-ray diffraction, thermogravimetric, and adsorption measurements were applied to study the thermal decomposition of the complexes of 25,26,27,28-tetrahydroxycalix[4]arene and 4-tert-butylcalix[4]arene with the solvents resulting in the formation of porous phases. Diffusion of the "guest" (solvent, gas) through the molecular crystal of calixarene-host proceeds via the consecutive formation of a series of thermodynamically unstable porous phases of the "host." Owing to the structural reorganization of calixarene, the transport of the "guest" occurs through the "host" matrix followed by complexation and formation of the thermodynamically stable structure.

A reaction of activated silicon with alcohols in an autoclave at 240—270 °C was studied. It was found that primary alcohols form tetraalkoxysilanes Si(OR)₄ with high selectivity (up to 97%), while the secondary PrⁱOH gave a mixture of compounds HSi(OPrⁱ)₃, Si(OPrⁱ)₄, HSi(OPrⁱ)₂OSi(OPrⁱ)₂H, HSi(OPrⁱ)₂OSi(OPrⁱ)₃, and Si(OPrⁱ)₃OSi(OPrⁱ)₃ with the predominance of trialkoxysilane (up to 67%). Carrying out the reaction under the indicated conditions has the advantage of experimental simplicity, reagent availability, high conversion of silicon, good isolated yields of products.

Parahydrogen-induced polarization technique (PHIP), based on the pairwise addition of molecular hydrogen to a substrate, was successfully applied to obtain novel information on the mechanisms of heterogeneous catalytic hydrogenation, hydrodesulfurization, and oligomerization processes. In particular, the PHIP effects were observed upon hydrogenation with parahydrogen catalyzed by the immobilized neutral complexes of rhodium and iridium, which confirms the similarity in the mechanisms of homogeneous and heterogeneous hydrogenation for such systems. In the study of acetylene oligomerization, a significant NMR signal enhancement was revealed for a number of C₄ oligomers, with the enhancement levels by far exceeding that observed in hydrogenation of carbon-carbon triple bonds. The mechanistic features of heterogeneous hydrogenation of a number of six-membered cyclic hydrocarbons over supported metal catalysts were investigated, and their hydrogenation scheme based on the pairwise addition of molecular hydrogen was proposed. Furthermore, the PHIP technique revealed that heterogeneous hydrodesulfurization of thiophene mainly proceeds via hydrogenation followed by a C—S bond cleavage. A significant enhancement of sensitivity in combination with characteristic line shapes of NMR signals make the PHIP method a unique and highly informative tool for the investigation of heterogeneous catalytic processes.

Carane-derived β-amino alcohols with amino and hydroxy groups at positions 3 and 4 differing in their mutual arrangement and configuration were synthesized. Their application as organocatalysts in the asymmetric aldol reaction of isatin with acetone allowed one to obtain adducts with up to 84% enantiomeric excess.

Efficient multigram two-step syntheses of 4-(2-chloroethoxy)phenol and 4-(3-chloropropoxy)phenol in >70% yields starting from 4-hydroxybenzaldehyde and reagents with general formula Cl(CH₂)_nX (X = Cl, n = 2; X = OTs, n = 3) are proposed. 4-(2-Chloroethoxy)phenol can also be conveniently prepared from 4-methoxyphenol and 1,2-dichloroethane. The compounds thus obtained can be used in carbohydrate chemistry to synthesize glycosides bearing "universal" 4-(ω-chloroalkoxy)phenyl aglycons.

Dibromoisocyanurate-mediated reaction of 4-amino-3-cyanofuroxans with pseudonitroles of aliphatic, alicyclic, and heterocyclic series (including pseudonitroles bearing ethylcarboxyl or additional nitro group) resulted in 4-(nitroalkyl- and dinitroalkyl-ONN-azoxy)-3-cyanofuroxans. Subsequent chemical transformations gave 4-(1,3-dinitrooxy-2-nitropropyl-2-ONN-azoxy)-3-cyano- and 4-carbamoylfuroxans, as well as 4-(1,1-dinitroethyl-ONN-azoxy)-3-(1H-tetrazol-5-yl)furoxans.

Simple and versatile synthetic procedures towards new aryl-substituted hydroxymethylphosphonic and methylenediphosphonic acids via reactions of either aromatic aldehydes or their derivatives with phosphites were elaborated.

A reaction of iodide [(η⁵-indenyl)IrI₂]_n (1) with thallium dicarbollide Tl[Tl(η-7,8-C₂B₉H₁₁)] leads to (indenyl)iridacarborane (η⁵-indenyl)Ir(η-7,8-C₂B₉H₁₁) (2) in 32% yield. The X-ray diffraction study showed that in the structure of 2, the five-membered rings C₅ and C₂B₃ have a cisoid conformation, in which the bridgehead carbon atoms of the indenyl ligand are arranged opposite to the carborane cage carbon atoms. The DFT calculations showed that the Ir—indenyl bond in compound 2 is weaker than the Ir—Cp bond in the complex (η-7,8-C₂B₉H₁₁)IrCp.

The process of non-catalytic hydrolytic polycondensation of dialkoxydiorganosilanes under elevated pressure has been investigated. It is shown that non-catalytic hydrolytic polycondensation of diethoxydimethylsilane in an autoclave proceeds with complete monomer conversion for 10 min forming predominantly linear oligomers. Complete conversion of diethoxymethylphenylsilane is achieved by stirring or by increasing of the process temperature. In the hydrolytic polycondensation of dialkoxydimethylsilanes in the autoclave without stirring the reactivity of monomer is regularly decreased with increasing of length of the alkoxy-groups in the series of MeO—EtO—PrⁱO—PrⁿO—BuⁿO.

A method for removal of erythrocyte ghosts from a biological medium without destruction of normal erythrocytes was developed on the basis of the electrochemical model of the blood—activated carbon system. It was shown that normal erythrocytes can be separated from erythrocyte ghosts by means of electrochemically controlled sorption on polarized activated carbons. The degree of removal of erythrocyte ghosts was found to depend on the potential and the nature of activated carbon. Erythrocyte stabilization on contact with the FAS brand carbon surface polarized to a potential of ~100 mV was found.

The yields of ⁶⁶Ga, ⁶⁷Ga, ⁶⁸Ga, ⁷⁰Ga, ⁶⁵Zn, and ^69mZn upon irradiation of gallium with the natural isotopic composition by the bremsstrahlung photon beam with the energy up to 55 MeV were measured. The yield of ^69mZn yield was 0.13 MBq μA^–1h^–1g^–1. A simple and rapid method for ^69mZn separation based on the extraction of gallium followed by ion-exchange chromatography was proposed.