Center for Magnetic Resonance

Yu. Kondratev, A. Butlak, I. Kazakov, A. Timoshkin

“Sublimation and thermal decomposition of ammonia borane: Competitive processes controlled by pressure”

Thermochim. Acta, 2015, in press
DOI:10.1016/j.tca.2015.08.021

Thermal behavior of ammonia borane BH3NH3 (AB) has been studied by calorimetry, tensimetry and mass spectrometry methods. It is shown, that depending on vapor pressure in the system two competitive processes are taking place at 357 K. At atmospheric pressure thermal decomposition with hydrogen evolution is the dominant process: BH₃NH_3(s) = 1/n (BH₂NH₂)_n(s) + H_2(g) (1). At low pressures (circa 4 mTorr) the major process is endothermic sublimation of AB: BH₃NH_3(s) = BH₃NH_3(g) (2). At intermediate pressures both processes occur simultaneously. Enthalpies for the processes (1) and (2) have been determined by drop-calorimetry method: Δ₍₁₎H_357° = −24.8 ± 2.3 kJ mol⁻¹ and Δ_subH_357°(BH₃NH₃) = 76.3 ± 3.0 kJ mol⁻¹. Solid products after sublimation and decomposition have been characterized by IR and NMR spectroscopy; gaseous forms were studied by mass spectrometry. Activation energy of 94 ± 11 kJ mol⁻¹ for the process (1) in range 327–351 K was determined by static tensimetry method. Based on the analysis of available thermodynamic characteristics, new values for the standard formation enthalpy of solid AB −133.4 ± 5.2 kJ mol⁻¹ and polyamidoborane −156.7 ± 5.8 kJ mol⁻¹ are recommended.

A.A. Beljaev, D.V. Krupenya, E.V. Grachova, V.V. Gurzhiy, A.S. Melnikov, P.Yu. Serdobintsev, E.S. Sinitsyna, E.G. Vlakh, T.B. Tennikova, S.P. Tunik

“Supramolecular AuI-CuI complexes as new luminescent labels for covalent bioconjugation”

Bioconjugate Chem., 2015
DOI:10.1021/acs.bioconjchem.5b00563

Two new supramolecular organometallic complexes, namely, [Au₆Cu₂(C₂C₆H₄CHO)₆(PPh₂C₆H₄PPh₂)₃](PF₆)₂ and [Au₆Cu₂(C₂C₆H₄NCS)₆(PPh₂C₆H₄PPh₂)₃](PF₆)₂, with highly reactive aldehyde and isothiocyanate groups have been synthesized and characterized using X-ray crystallography, ESI mass spectrometry, and NMR spectroscopy. The compounds obtained demonstrated bright emission in solution with the excited-state lifetime in microsecond domain both under single- and two-photon excitation. The luminescent complexes were found to be suitable for bioconjugation in aqueous media. In particular, they are able to form the covalent conjugates with proteins of different molecular size (soybean trypsin inhibitor, human serum albumin, rabbit anti-HSA antibodies). The conjugates demonstrated a high level of the phosphorescent emission from the covalently bound label, excellent solubility, and high stability in physiological media. The highest quantum yield, storage stability, and luminance were detected for bioconjugates formed by covalent attachment of the aldehyde-bearing supramolecular AuI–CuI complex. The measured biological activity of one of the labeled model proteins clearly showed that introduced label did not prevent the biorecognition and specific protein–protein complex formation that was extremely important for the application of the conjugates in biomolecular detection and imaging.

D.S. Ryabukhin, A.V. Vasilyev

“A synthesis of 4-aryl quinolin-2(1H)-ones by acidic zeolite promoted intramolecular cyclization of N-aryl amides of 3-arylpropynoic acids”

Tetrahedron Lett., 2015, 56, 2200-2202
DOI:10.1016/j.tetlet.2015.03.060

N-Aryl amides of 3-arylpropynoic acids are intramolecularly cyclized into 4-aryl quinolin-2(1H)-ones in high yields without any by-products under the action of acidic zeolite CBV-720 in benzene at 130 °C in a glass high pressure tube.

A.V. Galenko, A.F. Khlebnikov, M.S. Novikov, M.S. Avdontseva

“Synthesis of 3-(1,2-dioxoethyl)- and 2,3-dicarbonyl-containing pyrroles”

Tetrahedron, 2015, 71, 1940-1951
DOI:10.1016/j.tet.2015.02.030

The transition metal-catalyzed reaction of 2H-azirines with 1,2,4-tricarbonyl compounds leads to 3-(1,2-dioxoethyl)- and 2,3-dicarbonyl-pyrrole derivatives, useful building blocks for the preparation of 3-heterocyclyl pyrroles and pyrroles fused with heterocycles. The influence of catalysts and the reaction conditions on the yields of pyrroles and the regioselectivity of the reaction were studied. Experimental and theoretical results suggest that the reaction proceeds via the formation of an intermediate azirine–metal complex and subsequent nucleophilic N–C³ bond cleavage.

N.A. Danilkina, A.G. Lyapunova, A.F. Khlebnikov, G.L. Starova, S. Brase, I.A. Balova

“Ring-Closing Metathesis of Co₂(CO)₆–Alkyne Complexes for the Synthesis of 11-Membered Dienediynes: Overcoming Thermodynamic Barriers”

J. Org. Chem., 2015, 80, 5546-5555
DOI:10.1021/acs.joc.5b00409

The feasibility of ring-closing metathesis (RCM) as a synthetic entry to 10- and 11-membered dienediynes fused to a benzothiophene core was explored by experimental and theoretical investigations. An established sequence of iodocyclization of o-(buta-1,3-diynyl)thioanisoles followed by Sonogashira coupling to form diethynylbenzothiophenes was used to synthesize terminal benzothiophene-fused enediyne diolefins as substrates for RCM. Encountering an unexpected lack of reactivity of these substrates under standard RCM conditions, we applied DFT calculations to reveal that the underlying cause was a positive change in Gibbs free energy. The change in Gibbs free energy was also found to be positive for RCM of indole- and benzannulated terminal diolefins when affording smaller than 12-membered rings. We found that modification of the enediyne–diolefin substrate as the Co₂(CO)₆–alkyne complex allowed the target benzothiophene-fused 11-membered dienediyne to be obtained via RCM; the alkyne complexation strategy therefore provides one valid technique for overcoming challenges to macrocyclization of this kind.

O.A. Tomashenko, A.F. Khlebnikov, I.P Mosiagin, M.S. Novikov, E.V. Grachova, J.R. Shakirova, S.P. Tunik

“A new heterocyclic skeleton with highly tunable absorbtion/emission wavelength via H-bonding”

RSC Adv., 2015, accepted
DOI:10.1039/C5RA17755C

A new heterocyclic system, pyrido[2,1-a]pyrrolo[3,2-c]isoquinoline, was synthesized via Pd-catalyzed intramolecular cyclization of 1-[1-benzyl-2-(2-bromophenyl)-1H-pyrrol-3-yl]pyridin-1-ium bromides. The heterocycles obtained display stimuli responsive fluorescence in solution depending on the nature of the solvent. The strongest blue shift of the emission maxima and growth in luminescence intensity was observed in protic solvents and upon addition of proton donors to solutions of compounds in aprotic solvents. The effect of proton donors on emission characteristics was explained by DFT calculations in terms of H-complex formation with the nucleophilic centres of the molecular skeleton

A.D. Lisakova, D.S. Ryabukhin, R.E. Trifonov, V.A. Ostrovskii, A.V. Vasilyev

“Alkylation of 5-substituted NH-tetrazoles by alcohols in the superacid CF₃SO₃H”

Tetrahedron Lett., 2015, 56, 7020-7023
DOI:10.1016/j.tetlet.2015.11.005

Reactions of 5-substituted NH-tetrazoles with alcohols in the superacid CF3SO3H have been studied. Both the structure of the tetrazole and the nature of alcohol were found to dramatically influence the selectivity of the reaction and yields of products. Tetrazoles bearing phenyl, electron-donating aryl, or benzyl groups at the 5-position, have been alkylated using various alcohols (including MeOH and EtOH) in CF₃SO₃H upon heating at 60 °C for 0.3–12 h to afford 2-alkyl-2H-tetrazoles in 30–98% yields.

K.S. Rodygin, V.P. Ananikov

“An efficient metal-free pathway to vinyl thioesters with calcium carbide as the acetylene source”

Green Chemistry, 2015, accepted
DOI:10.1039/c5gc01552a

Chemical reactions involving high-pressure acetylene are not easily performed in a standard laboratory setup. The risk of explosion and technical difficulties drastically complicate the equipment and greatly increase the cost. In this study, we propose the replacement of acetylene with calcium carbide, which was successfully utilized to synthesize practically useful vinyl thioesters in accordance with a simple and environmentally benign procedure. The reaction proceeded under mild conditions using a standard laboratory setup. The optimized reaction conditions allowed the selective synthesis of the vinyl thioesters in high yields, and the reaction conditions can be scaled up to synthesize grams of sulfides from inexpensive starting materials.

A.P. Molchanov, E.V. Sirotkina, M.M. Efremova, R.R. Kostikov, A.V. Ivanov, V.S. Shcherbakova

“Regio- and Stereoive Cycloaddition of Nitrones to 1-Vinyl-4,5-dihydro-1Н-benzo[g]indole”

Russ. J. Org. Chem., 2015, 51, 640-643
DOI:10.1134/S1070428015050097

Nitrones cycloaddition to 1-vinyl-4,5-dihydro-1Н-benzo[g]indole proceeds regio- and steroselectively affording a single diastereomer of 5-(hetaryl-substituted)isoxazolidine.

I.S. Ignatyev, T.A. Kochina, V.V. Avrorin, V.V. Gurzha, I.M. Fundamensky

“Molecular and crystal structure of 2-phenyl-2-hydro-6-methyl-1,3-dioxa-6-aza-2-silacyclooctane”

J. Molec. Struct., 2015, 1094, 169-173
DOI:10.1016/j.molstruc.2015.03.061

The crystal structure of 2-phenyl-2-hydro-6-methyl-1,3-dioxa-6-aza-2-silacyclooctane [HPhSi(OCH₂CH₂)₂NMe – phenylhydrosilocane (I)] is determined by single-crystal X-ray diffraction at 100 K. The unit cell consists of four molecules connected only by Van-der-Waals interactions. Each molecule has an eight-membered heterocycle with a phenyl group in the axial position. The Si⋯N transannular bond has a short (2.206 Å) interatomic distance which exceeds only this distance in ocanes with highly electronegative fluorine substituents at Si. Since there exist experimental data on the occurrence of different conformers of I in the liquid phase, the PES of the molecule was analyzed by DFT B3LYP and MP2 methods with the aug-cc-pVDZ basis set. The energy minimum belongs to the boat–chair conformation with the axial position of the phenyl group. Rotation of the phenyl ring around the SiC bond has a barrier ca. 1 kcal/mol. The conformer with the equatorial position of this group lies 6 kcal/mol higher. Interconversion of this conformers which was observed in experiment proceeds through the chair–chair configuration in which the Si⋯N transannular bond is absent and coordination at silicon is tetrahedral, rather than trigonal bipyramidal one observed in other conformers.