V. B. Rybakov

Vanadium peroxocomplexes as oxidation catalysts of sulfur organic compounds by hydrogen peroxide in bi-phase systems

Abstract New vanadium oxodiperoxocomplexes Bu4N+[VO(O2)2 L2]− were synthesized, where L=pyridine (1), 2-methylpyridine (2), 4-methylpyridine (3), 2-oxymethylpyridine (4). All complexes were characterized by NMR ( 1 H , 51 V ) and IR spectroscopy. The oxidation of sulfur organic compounds and diesel fuel desulfurization catalyzed by vanadium peroxocomplexes in bi-phase system was investigated in various solvents. The complexes manifested high catalytic activity and selectivity in oxidation of sulfides.

Crystal and molecular structure of bis(tetramethylcyclopentadienyl)titanium halides, (C5HMe4)2TiCl, (C5HMe4)2 TiI and (C5HMe4)2 TiCl2

Abstract X-ray analysis of (C 5 HMe 4 ) 2 TiCl ( I ), (C 5 HMe 4 ) 2 TiI ( II ) and (C 5 HMe 4 ) 2 TiCl 2 ( III ) revealed that their overall geometry is very similar to that of permethylated (C 5 Me 5 ) 2 TiCl 2 ( IV ) and (C 5 Me 5 ) 2 TiCl 2 ( V ) complexes. The general structural difference between the C 5 Me 5 and C 5 HMe 4 bent sandwich compounds is a larger CE-Ti-CE angle (by approx. 4°; CE is the centroid of the Cp ring) in the latter compounds which apparently results from a release of steric strain in the C 5 Me 5 derivatives upon replacement of Me groups by hydrogen atoms in positions of close approach of cyclopentadienyl rings. Another difference lies in a shift of the Ti atom from the symmetrical position with respect to the C 5 HMe 4 ring towards the top of the dihedral angle. Comparison of structures I and II shows that the nature of the halogen atom does not affect the CE-Ti-CE angle in the titanocene skeleton.

Novel route to b-fused thiazoles starting from a 2-chloro-1-phenacylpyridinium salt and KSCN. Crystal structures of thiazolo- and oxazolo[3,2-a]pyridinium thiocyanates

Abstract Reaction of 2-chloro-1-phenacylpyridinium bromide 1a with KSCN led to 2-amino-thiazolo[3,2-a]pyridinium salts 4a,b thus opening a novel route to fused thiazoles. In reaction with KSCN oxazolo[3,2-a]pyridinium perchlorate 2a was converted to thiocyanate 2b . Crystal structures of thiocyanates 2b and 4b were determined.

An Improved Synthesis of Some 5-Substituted Indolizines Using Regiospecific Lithiation

Various 2-substituted indolizines can be directly and selectively lithiated in the 5 position and subsequent reactions with different electrophiles lead to some novel classes of indolizines. In particular, previously unknown 5-formyl- and 5-iodoindolizine have been prepared by this way and the molecular structure of 5-formyl-2-phenylindolizine was confirmed by X-Ray analysis. The reactivity of the 5-CHO- and 5-COPh groups toward some nucleophiles has been examined, and some additional classes of derivatives (oximes and alcohols) have been obtained. The possibility of Suzuki cross-coupling of 5-iodoindolizines and boronic acids was proven.

Heterocyclic Compounds with a Bridge Nitrogen Atom. 14. Cycloaddition of Acetylenedicarboxylic Acid Ester to 2-Chloro-N-phenacylpyridinium Ylide. Crystal Structure of Dimethyl Ester of 5-Chloro-3-(p-nitrobenzoyl)indolizine-1,2-dicarboxylic Acid

Derivative of 5-chloroindolizine is formed in the reaction of 2-chloro-1-(p-nitrophenacyl)pyridinium ylide with acetylenedicarboxylic acid dimethyl ester, the structure of which was demonstrated by X-ray diffraction analysis. According to data of 1H NMR and mass spectra indolizine obtained undergoes an unusual intramolecular cyclization with the formation of benz[e]cycl[3.3.2]azine nucleus.

Influence of the dopant type on point defects in PbMoO4 crystals

Nominally pure and Nd3+-doped single crystals of PbMoO4 grown by the Czochralski method with the use of Nd2O3, Nd2(MoO4)3, NaNd(MoO4)2, and NdNbO4 compounds are investigated by the methods of single-crystal and powder X-ray diffraction analysis, single-crystal neutron diffraction, and impedance spectroscopy. The types and concentration of point defects are determined. Their effect on the dielectric properties of crystals is hypothesized. It is established that the color of the crystals is caused by the formation of color centers.

Heterocycles containing a bridge nitrogen atom. 10. Unexpected closure of oxazole ring during the reaction of 2-chloro-1-phenacylpyridinium salt with potassium cyanate. Crystal structure of 2-(p-nitrophenyl)oxazolo-[3,2-a]pyridinium bromide and N-(p-nitrophenacyl)pyrid-2-one

Reaction of 2-chloro-N-(p-nitrophenacyl)pyridinium bromide with potassium cyanate in acetonitrile produces 2-(p-nitrophenyl)oxazolopyridinium bromide. Performing the same reaction in methanol N-(p-nitrophenacyl)pyrid-2-one was isolated. The structures of the obtained products were proved by X-ray structural data.

Crystal structures of strontium and barium ethylenediaminetetraacetato cobaltates(III), Sr[CoEdta]2·9H2O and Ba[CoEdta]2·8H2O: Comparison of the structures of complexes in the series M’[CoEdta]2·nH2O (M’ = Mg, Ca, Sr, Ba; n = 7–10)

Cobalt(III) complexes, namely, Sr[CoEdta]2·9H2O (I) and Ba[CoEdta]2·8H2O (II) (where Edta4- is the ethylenediaminetetraacetate ion), are synthesized. The crystal structures of these compounds are determined using X-ray diffraction. Crystals of compound I are triclinic, a = 6.514(1) Å, b = 11.410(2) Å, c = 12.317(2) Å, α = 67.87(1)°, β = 88.73(2)°, γ = 84.22(2)°, V = 843.63(3) Å3, Z = 1, space group P1, and R = 0.0295 for 4130 reflections with I > 2σ(I). Crystals of compound II are monoclinic, a = 6.543(2) Å, b = 12.895(3) Å, c = 19.489(4) Å, β = 95.24(3)°, V = 1637.5(5) Å3, Z = 2, space group P21, and R = 0.050 for 3016 reflections with |F| > 3σ(|F|). The structures of compounds I and II are compared with those of the previously studied complexes Mg[CoEdta]2·10H2O (III) and Ca[CoEdta]2·7H2O (IV). The crystal structure of the cobalt(III) complex with the strontium cation (I) is topologically similar to the crystal structure of cobalt(III) complex with the calcium cation (IV). The former structure is built up of the two symmetrically independent homochiral anionic complexes [CoEdta]− (AI and BI), the aqua cations [Sr(H2O)8]2+, and the molecules of crystalization water wcr. The structure of compound II involves two independent anions [CoEdta]− (AII and BII) with different chiralities (i.e., they are kryptoracemates). The AII anions are linked via the barium cations into {Ba(H2O)7[CoEdta]}1∞+ chain agglomerates due to the incorporation of two terminal oxygen atoms Ou of the anions neighboring in the chain into the coordination sphere of the barium atom. All four structures (I–IV) contain stacks composed of the [CoEdta]− homochiral anions forming layers aligned parallel to the (001) plane. The aqua cations [Sr(H2O)8]2+, [Mg(H2O)6]2+, and [Ca(H2O)7]2+ or the partially hydrated barium cations [Ba(H2O)7(Ou)2]2+ (in structure II), as well as water molecules wcr, are located between the anion layers. The octahedral environment of the cobalt(III) atoms consists of donor atoms (2N and 4O) of the Edta4− ligand. The Co-N bonds in the AI, BI, AII, and BII anions [the mean bond lengths are 1.927(4), 1.921(4), 1.910(6), and 1.921(6) Å, respectively] are considerably longer than the Co-O bonds [the mean bond lengths are 1.908(5), 1.902(5), 1.904(6), and 1.908(6) Å, respectively]. The mean distances Sr-Ow and Ba-Ow in the strontium and barium polyhedra are 2.609(4) and 2.834(8) Å, respectively. The mean distance Ba-Ou is 2.814(7) Å.

Growth and Neutron Diffraction Investigation of Ca3NbGa3Si2O14 and La3Ga5.5Nb0.5O14 Crystals

Langanite (La3Ga5.5Nb0.5O14, growth atmosphere: 99% Ar + 1% O2) and kanigasite (Ca3NbGa3Si2O14, growth atmosphere: 100% Ar) crystals grown by the Czochralski technique in Ir crucibles along direction have been firstly investigated by neutron diffraction. The difference between the compositions of upper (La2.935(2)□0.065)(Ga0.450Nb0.550(3))Ga3(Ga1.965(4)□0.035)(O13.90(1)□0.10) and lower (La2.940(1)□0.060)(Ga0.590Nb0.410(2))Ga5(O13.82(1)□0.18) parts of orange langanite crystal was found. It was established that the colorless Ca3NbGa3Si2O14 crystal grown by using the single-crystal charge has the composition (Ca2.95□0.05(1))NbGa3Si2O14 and is less defective in comparison to the yellow one grown by using the charge prepared by conventional solid-state reaction. For Ca3NbGa3Si2O14 and La3Ga5.5Nb0.5O14 crystals the possibility of microtwin formation (two unit cells connected by the translation: 1/2 z) was revealed for the first time. It was found that the difference between the color of crystals is attributed to the qualitative differentiation of oxygen vacancies.

4-Hydroxy-2-quinolones. 38. Synthesis, structure, and anticonvulsant activity of optically active 1-phenylethylamides of 1-R-4-hydroxy-2-oxo-3-quinolinecarboxylic acids

A synthesis is reported for optically pure antipodes of 1-phenylethylamides of 1-R-4-hydroxy-2-oxo-3-quinolinecarboxylic acids. An attempt was made to establish the absolute configuration of these products by X-ray diffraction crystallographic analysis. The anticonvulsant activity of the S-enantiomers was studied.