Volume 66, Nº 9 (2017)

N-Heterocyclic carbenes (NHCs) are widely used as ligands in catalysis by transition metal complexes. The catalytic activity of transition metal NHC complexes is much higher than that of the transition metal complexes bearing the phosphine and nitrogen-containing ligands. They show excellent catalytic performance in different transformations of the organic compounds, especially in the carbon—carbon and carbon—element bond forming reactions. Palladium NHC complexes are very efficient catalysts for the cross-coupling reactions. On the other hand, nickel is less expensive and regarded as a promising alternative to palladium and, therefore, it attracts increasing attention from the researches. The present review is focused on the recent advances in the synthesis of N-heterocyclic carbene complexes of nickel and palladium and their application in catalysis of cross-coupling reactions of organic, organoelement and organometallic compounds with organic halides.

The adsorption of CH₂Cl₂, CH₃Cl, CCl₄, and H₂O vapors on the surface of multi-walled carbon nanotubes and alumina in the temperature range of 10—25 °C was studied. Dependences of the isosteric heat of adsorption on the surface coverage were plotted. The initial heat of adsorption of dichloromethane, chloroform, and CCl₄ on Al₂O₃ was found to be equal to 71, 28, and 31 kJ mol^–1, respectively. In most cases, adsorption on the oxide adsorbent was characterized by a higher heat of adsorption compared to that found on the carbon material, which is apparently related to chemical interaction of sorbed molecules with the OH groups of the alumina surface.

The results of geometric analysis of 588 crystal structures of square-planar nickel complexes containing short intermolecular Ni…X contacts (X is a non-metal atom) are reported. The frequency of occurrence of Ni…X interactions of a particular type was evaluated depending on the nature of the X atom and geometric characteristics. The promolecular functions RDG and sign(λ₂)•ρ(r) were used to analyze the character of Ni…X interactions in attractive/repulsive terms. The relative strength of these interactions was determined as the function of the nature of the X atom and the direction of charge transfer.

New tri- and tetranuclear macrocyclic silver(i) and copper(i) 3-ferrocenyl-5-(trifluoromethyl)pyrazolates were prepared: [{(3-((η⁵-C₅H₄)Fe(η⁵-C₅H₅))-5-(CF₃)-Pz}M]₃ (M = Cu (1), Ag (2)) and [{(3-(( η⁵-C₅H₄)Fe(η⁵-C₅H₅))-5-(CF₃)-Pz}Cu]₄ (3). The structures of compounds were established by X-ray diffraction analysis. In the crystalline state, a planar trinuclear silver-containing macrocycliс pyrazolate and a saddle-shaped tetranuclear copper-containing macrocycle are formed. The introduction of a bulky substituent, ferrocene, into the pyrazole ligand results in complete shielding of the acidic metal sites, which precludes the coordination of base molecules.

Two metal-organic coordination polymers based on cadmium(ii) ions and terephthalic (1,4-benzenedicarboxylic) acid were synthesized in dimethylformamide or a mixture of dimethylformamide and methanol: [Cd₃(bdc)₃(dmf)₄] (1, bdc is 1,4-benzenedicarboxylate, dmf is N,N´-dimethylformamide) and [Cd₃(bdc)₃(dmf)₂] (2), respectively. According to the single-crystal X-ray diffraction data, both compounds are built up by the trinuclear carboxylate units {Cd₃(O₂CR)₆}. Compound 1 has a layered structure, whereas compound 2 has a three-dimensional structure due to the presence of additional coordination interactions between adjacent trinuclear units and the formation of polymer chains {Cd₃(dmf)₂(μ₂-O₂CR-κ¹,κ¹)₂(μ₂-O₂CR-κ²,κ¹)₄(O₂CR-κ¹)2}. The synthesized compounds were characterized by IR spectroscopy, thermogravimetric analysis, elemental analysis, and powder X-ray diffrac- tion. The luminescence properties of these compounds provide evidence for the existence of both intraligand and charge-transfer transitions. The luminescence quantum yields for both compounds are 10%.

A reaction of methyl 2-(4-allyl-2-methoxyphenoxy)acetate with adamantan-2-amine and (adamantan-1-yl)methylamine in butanol leads, together with the target amides, to the formation of butyl ester of the corresponding acid, which is resistant to aminolysis.

An efficient synthetic procedure to combine biologically active indole derivatives by the triazole-containing spacer in a molecule has been proposed. The procedure was based on a copper-catalyzed alkyne-azide cycloaddition of azide-containing carbazoles and N-propargyl-containing carbazoles, tetrahydrocarbazoles, and tetrahydro-γ-carbolines.

A series of six-coordinate magnesium bis-3,6-di-tert-butyl-о-benzosemiquinonate complexes with different N-donor ligands (2,2´-dipyridyl, 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, pyridine, N-phenyl-1-(4-pyridinyl)methanimine) were synthesized. The molecular and crystal structures of these complexes were determined by X-ray diffraction. In the complexes with bidentate N-donor ligands, the O,O-diolate o-semiquinone ligands are cis to each other, whereas the compounds with monodentate ligands contain organic radical anions in trans positions. The specific features of magnetic exchange coupling between organic radical ligands were studied by temperature-dependent magnetic susceptibility measurements.

The transylidation between 1,4-dichloro-3a,6a-diaza-1,4-diphosphapentalene and benzylidenetriphenylphosphorane (Ph₃P=CHPh) results in either mono- or disubstitution of chlorine atoms by the Ph₃P=C(Ph) group depending on the reactant molar ratio. In the crystal, the monosubstituted product has the planar diazadiphosphapentalene ring and the P—Cl ionic bond. The ³¹P NMR spectra of this compound exhibit a strong solvent-dependent behavior, which indicates that it exists both in the ionic form (in CH₂Cl₂, MeCN) and the molecular form (in THF). In the disubstituted product, the diazadiphosphapentalene skeleton is non-planar and is bent along the N—N bond.

The influence of bis[4,6-di-tert-butyl-N-(2,6-dimethylphenyl)-o-iminobenzosemiquinonato]cobalt(ii) and 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-iminobenzosemiquinonato]-[4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-amidophenolate]manganese(iii) on polymerization of methyl methacrylate and acrylonitrile in the presence of azobisisobutyronitrile (as a traditional radical initiator) and alkyl halides (used for initiation of controlled atom transfer radical polymerization process) was studied. The effect of the nature of the activating agents (amines) and the temperature conditions on the overall polymerization rate of the indicated monomers, as well as molecular weight characteristics of the synthesized polymers, were analyzed. The optimal conditions for the synthesis of polyacrylonitrile and poly(methyl methacrylate) with a relatively narrow molecular weight distribution were selected.

A new triketimine (2,6-Me₂C₆H₃N=CMe)₂CH(2,6-Me₂C₆H₃N=CBu^t) (1) was synthesized by the reaction of imidoyl chloride 2,6-Me₂C₆H₃N=CClBu^t with lithium diketiminate (2,6-Me₂C₆H₃N=CMe)₂CHLi. In the crystalline state, compound 1 exists in the diimineenamine form; in solution, in the triimine form. The metalation of triketimine 1 with n-butyllithium in THF at 0 °C produced lithium triketiminate [(2,6-Me₂C₆H₃N=CMe)₂C(2,6-Me₂C₆H₃N=CBu^t)]Li(THF)₂ (2). The metathesis reactions of Ln(BH₄)₃(THF)₃ (Ln = Y, Nd) with compound 2 (1: 1 molar ratio, THF) gave the neutral triketiminate bis(borohydride) complexes [(2,6-Me₂C₆H₃N=CMe)₂C(2,6-Me₂C₆H₃N=CBu^t)]Ln(BH₄)₂(THF)₂ (Ln = Y (3), Nd (4)). As opposed to the complexes with neutral triketimine, the monoanionic triketiminate ligand is coordinated to Li and Y or Nd cations in a bidentate fashion. Complexes 3 and 4 catalyze the polymerization of rac-lactide and ε-caprolactone; in combination with [Ph₃C][B(C₆F₅)₄] and AlBu₃ⁱ (1 : 1 : 10 molar ratio), these compounds exhibit catalytic activity in the polymerization of isoprene.

High-resolution electrospray ionization mass spectra (MS and MS/MS) of a series of glycoconjugates containing biotin and oligomannuronopyranosyl residues linked via a hexaethylene glycol spacer were recorded in the positive and negative ion modes and interpret. In collision activation mass spectra of the positively charged ions (CID MS²), two series of the most abundant peaks were attributed to the fragments resulting from a glycosidic bond cleavage with localization of a charge at either reducing (Y series) or non-reducing end (B series). Fragmentation of hexaethylene glycol chain observed at relatively high activation energies (30 eV or higher) occurred predominantly at the C—O bond most distant from the biotin moiety. In the mass spectra of the negatively charged ions of the studied compounds, the peaks of B, C, and Z series (a systematic nomenclature for carbohydrate fragmentations was used) were present along with the peak analogous to the aforementioned one, which arose from the cleavage of the same C—O bond. The distinctive feature of the fragmentation of the negative ions is the elimination of H₂S and H₂CS from the biotin moiety.

It is shown for the first time using a complex of physicochemical methods (dynamic and electrophoretic light scattering, conductometry, pH-metry) that below a threshold concentration of 1.0•10^–7 mol L^–1 the disperse phase of the aqueous systems based on moss peptide PpCLE2 undergoes the domain—nanoassociate rearrangement, which affects the nonmonotonic concentration dependences of the specific electrical conductivity and pH and can result in a multidirectional profile of the dependence of the growth of the primary and lateral roots of the Arabidopsis thaliana seed plant in the range of calculated concentrations from 1.0•10^–6 to 1.0•10^–12 mol L^–1.

Analysis of levoglucosan by ligand-exchange chromatography with UV detection showed deviations from the Bouguer—Lambert—Beer law. Their character allowed us to suggest that the deviations are caused by the formation of levoglucosan supramers in the eluent.