Center for Magnetic Resonance

M.Ya. Demakova, D.S. Bolotin, N.A. Bokach, R.M. Islamova, G.L. Starova, V.Yu. Kukushkin

“Click-Type PtII-Mediated Hydroxyguanidine–Nitrile Coupling Provides Useful Catalysts for Hydrosilylation Cross-Linking”

ChemPlusChem, 2015, 80, 1607-1614
DOI:10.1002/cplu.201500327

The nitrile complexes trans-[PtCl₂(RCN)₂] (R=Et (NC1), tBu (NC2), Ph (NC3), p-BrC₆H₄ (NC4)) and cis-[PtCl₂(RCN)₂] (R=Et (NC5), tBu (NC6), Ph (NC7)) react with 1 equiv of the hydroxyguanidine OC4H8NC(=NOH)NH2 (HG) furnishing the mono-addition products trans- and cis-[PtCl₂(RCN){NH=C(R)ON=C(NH₂)NC₄H₈O}] (1–4 and 9–11; 7 examples; 54–74 % yield). Treatment of any of the nitrile complexes NC1–NC7 with HG in a 1:2 molar ratio generated the bis-addition products trans- and cis-[PtCl₂{NH=C(R)ON=C(NH₂)NC₄H₈O}₂] (5–8 and 12–14; 7 examples; 69–89 % yield). The PtII-mediated coupling between nitrile ligands and HG proceeds substantially faster than the corresponding reactions involving amid- and ketoximes and gives redox stable products under normal conditions. Complexes 1, 6⋅4 CH₂Cl₂, 7⋅4 CH₂Cl₂, 8⋅2 CH₂Cl₂, and NC4 were studied by X-ray crystallography. Platinum(II) species 1–3, 10, 11, and especially 9, efficiently catalyze the hydrosilylation cross-linking of vinyl-terminated poly(dimethylsiloxane) and trimethylsilyl-terminated poly(dimethylsiloxane-co-ethylhydrosiloxane) giving high-quality thermally stable silicon resins with no structural defects. The usage of these platinum species as the catalysts does not require any inhibitors and, moreover, the complexes and their mixtures with vinyl- and trimethylsilyl-terminated polysiloxanes are shelf-stable in air.

A.S. Smirnov, E.S. Yandanova, N.A. Bokach, G.L. Starova, V.V. Gurzhiy, M.S. Avdontceva, A.A. Zolotarev, V.Yu. Kukushkin

“Zinc(II)-mediated generation of 5-amino substituted 2,3-dihydro-1,2,4-oxadiazoles and their further ZnII-catalyzed and O2-involving transformations”

New J. Chem., 2015, 12, 9330-9344
DOI:10.1039/C5NJ02061A

Zn^II-activated cyanamides NCNR₂ (R₂ = Me₂, Et₂, C₅H₁₀, (CH₂)₂O(CH₂)₂, Ph₂) react with the acyclic N-alkyl ketonitrones Ph₂C[double bond]N+(O−)R′ (R′ = Me, CH₂Ph) and N-aryl ketonitrones (R′ = Ph, p-BrC₆H₄, p-EtC₆H₄) under mild conditions. Uncomplexed 5-aminosubstituted 2,3-dihydro-1,2,4-oxadiazoles (6 examples; 49–82%) were obtained in zinc(II)-involving cycloaddition of the N-alkyl ketonitrones to the cyanamide substrates; these 2,3-dihydro-1,2,4-oxadiazoles undergo ring-opening giving carbamoylamidines and methylidenureas. The N-aryl ketonitrones react with ZnII-activated cyanamides giving the open-chain systems, viz. carbamoylamidines, N′-(2-(diphenylmethylidene)amino)-phenyl-N,N-carbamimidic acids, and methylidenureas, which are presumably formed via the cycloaddition route followed by the N–O cleavage induced by the acceptor character of the aryl groups.

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.