Showing papers by "Andrei V. Churakov published in 2007"

4-Styrylquinolines: synthesis and study of [2 + 2]-photocycloaddition reactions in thin films and single crystals

Abstract: Four new (E)-4-styrylquinoline compounds containing two methoxy substituents or an 18-crown-6-ether fragment were synthesized in order to investigate the [2 + 2]-photocycloaddition (PCA) reaction in the solid state. These compounds reveal different abilities to undergo the photoreaction depending on the packing of the quinoline molecules in thin polycrystalline films and single crystals. The only products from the irradiation of (E)-4-styrylquinolines were an rctt isomer of 1,2,3,4-tetrasubstituted cyclobutane and, rarely, a Z isomer of the styrylquinoline. The rctt cyclobutane derivative was formed as a result of the PCA of centrosymmetric syn-‘head-to-tail’ dimeric pairs of the reactant species that are preorganized in such a way as to promote this reaction. Peculiarities in the crystal packing motifs that are typical for single crystals of 4-styrylquinoline compounds are discussed. The solvate molecules can affect significantly the packing of styrylquinolines. Benzene solvate molecules create a soft, flexible, shell about the dimeric pairs that facilitates the PCA in the single crystal without causing degradation of the crystal. In crystal packing that contains CH2Cl2 and H2O solvate molecules, they are prone to form complicated systems of hydrogen bonds with crown-ether oxygen atoms and each other. This results in distorting the organic molecule geometry toward non-planarity and accomplishing a new type of crystal packing uncommon for styrylheterocycles, in which the PCA is impossible. The topochemical single-crystal-to-single-crystal PCA reaction was monitored for one of the species. Two cyclobutane derivatives obtained in single crystals were subjected to recrystallization from a solution. The new single crystals formed belong to different crystal systems, with different unit cell parameters as compared with initial single crystals; significant differences in the geometry of the cyclobutane molecules were also found. This implies that the cyclobutane derivatives obtained in the solid phase have a molecular geometry that is somewhat stressed.

Styryl dyes. Synthesis and study of the solid-state [2+2] autophotocycloaddition by NMR spectroscopy and X-ray diffraction

Abstract: New styryl dyes of the pyridine and benzothiazole series were synthesized with the aim of investigating the solid-state [2+2] autophotocycloaddition (PCA) reaction. The 1H NMR spectroscopy showed that for most of the compounds under study, the visible light irradiation of thin polycrystalline films of the dyes affords cyclobutane derivatives. The rate of the photoreaction depends on the structure of the dye and is higher for compounds, which contain a short N-substituent in the heterocyclic moiety and have strong absorption in the visible region. Dyes bearing electron-releasing substituents in the benzene ring undergo the stereospecific PCA in the syn-head-to-tail dimeric pair to give the only rctt isomer of cyclobutane derivatives. Electron-withdrawing and bulky substituents in the benzene fragment of styryl dyes extend the range of the mutual orientations of the molecules in the dimeric pairs, resulting in the formation of two or even four isomeric cyclobutanes in the PCA reactions. The structures of some dyes were established by X-ray diffraction. In the overwhelming majority of the structures, one of two packing modes, either syn-head-to-tail or syn-head-to-head, with extensive stacking interactions is observed. A rare example of the anti-head-to-head stacking mode was found for the dicationic dye containing the bulky N+(Et)Me2 substituent in the benzene ring. The syn-head-to-tail and anti-head-to-head stacking modes can facilitate the PCA reaction due to the close spatial proximity of the ethylenic bonds and their parallel orientation in the dimeric pairs of the dye molecules.

Thymine hydrogen peroxide 0.55‐solvate 0.45‐hydrate

Abstract: Thymine crystallizes from 50% hydrogen peroxide to give the title hydrogen peroxide water solvate, C5H6N2O2·0.55H2O2·0.45H2O. The disordered peroxide and water mol­ecules occupy the same positions. Thymine mol­ecules are linked together by N—H⋯O hydrogen bonds forming chains parallel to the ac diagonal. Hydrogen peroxide mol­ecules are combined by O—H⋯O hydrogen bonds to give chains parallel to the c axis. Both kinds of chains are organized in a three-dimensional hydrogen-bonded network.

Syntheses and structures of asymmetric Bis(silyl) niobocene hydrides.

Abstract: This paper deals with the preparation and structural investigation of asymmetric bis(silyl) niobocene hydrides, Cp2Nb(SiHMe2)(H)(SiXMe2) (2; X = F (a), Cl (b), Br (c), I (d)) and Cp2Nb(SiXMe2)(H)(S...

Synthesis and structural studies of germyl and germyl/stannyl substituted tungstenocenes.

Abstract: One-pot reactions of [WCp2(H)2] and [WCp2(H)(SnMe3)] with nBuLi followed by an equivalent of GeMe2Cl2 afford mono(germyl) substituted tungstenocenes [WCp2(H)(GeMe2Cl)] (1) and [WCp2(SnMe3)(GeMe2Cl)] (7). Reactions of the products with tin halides in the presence NEt3 afford the mixed complexes [WCp2(SnR2X)(GeMe2Y)] (X, Y = Cl, Br, RMe, Et), which were further converted to moderately stable compounds [WCp2(SnR2H)(GeMe2H)] (R = Me (10), Et (11)). A number of asymmetric mono(halo)-substituted germyl/stannyl tungstenocenes [WCp2(SnMe2X)(GeMe2H)] (X = Cl (12), Br (13)) and [WCp2(SnEt2Y)(GeMe2H)] (Y = Br (14), I (15)) were prepared by selective halogenation of the Sn–H bond in 10 and 11. X-Ray studies of [WCp2(H)(GeMe2Cl)] (1), [WCp2(SnEt2Br)(GeMe2Cl)] (4), and [WCp2(SnEt2Br)(GeMe2H)] (14) established classical structures of these compounds. X-Ray study of complex [WCp2(SnMe2Cl)(GeMe2Cl)] (3) revealed the presence of interligand Ge–Cl⋯Sn–Cl interactions in a highly Ge/Sn disordered structure. Analyses of molecular parameters of 1, 4, and 14 suggest the presence of a negative hyperconjugation between metal lone pairs and the σ*-orbital of the E–X bond, which is stronger in bromo substituted complexes in comparison with chloro substituted ones.

Synthesis and crystal structure of new alkali metal hydrogen tellurates

Abstract: New alkali metal hydrogen tellurates have been synthesized, and their structures have been determined by X-ray crystallography. Hydrogen tellurates I–VI contain centrosymmetric binuclear anions [Te2O10H4+x](4−x)−, where x=0, 1, 2. Hydrogen tellurates II and VI contain, in addition to the binuclear anion, mononuclear species [TeO6H4]2− and Te(OH)6, respectively. The CNs of alkali metals vary from 8 to 12. In all structures, the hydrogen atoms (of both the hydroxy groups and water molecules) are involved in hydrogen bonding.

Benzyl N,N-bis[2-(pentafluoroanilino)ethyl]carbamate.

Abstract: The title compound, C24H17F10N3O2, exhibits intramolecular N-H...O hydrogen bonding, as well as intramolecular Ar...Ar(F) face-to-face interactions. The molecules are linked together by N-H...F-C hydrogen bonds, forming chains parallel to the a axis. Adjacent symmetry-related chains are combined in double zipper-like ribbons by parallel Ar(F)...Ar(F) offset pi-stacking interactions.

Synthesis and Spectroscopic and Structural Studies of Cross-Conjugated Dienones Derived from Cyclic Ketones and Aromatic Aldehydes.

Abstract: Cross-conjugated dienones were synthesized by the reactions of cyclic ketones with two equivalents of aromatic aldehydes under basic conditions. An NMR spectroscopic study and X-ray diffraction analysis demonstrated that all reaction products are formed as E,E isomers. Spontaneous photochemical trans-cis isomerization of cross-conjugated dienones under the scattered light in solution was observed for the first time. The degree of isomerization depends mainly on the nature of the central fragment of the dienone molecule. The previously unknown product of photochemical [2+2]-cycloaddition of 2,5-bis[(E)-(3-pyridyl)methylidene]cyclopentanone was synthesized and characterized by spectroscopic methods and X-ray diffraction. Under the conditions used, only one isomer of the cyclobutane adduct was obtained.