Resolution and determination of the absolute configuration of 3,3′4,4′-tetramethyl-1,1′-diphosphaferrocene-2-carboxylic acid

(±)-3,3′4,4′-Tetramethyl-1,1′-diphosphaferrocene-2-carboxylic acid 1 was resolved via diastereomeric salts with brucine. The (R)-absolute configuration of (+)-1 was determined by X-ray crystallography.     

Synthesis and characterization of complexes of the first transition series cations with 2,2′-biimidazole and 2,2′-biimidazolate

Mononuclear [M(hfacac)₂(H₂biim)] complexes, where M = Mn^II, Fe^II, Co^II, Ni^II, Cu^II or Zn^II, hfacac = hexafluoroacetylacetonate, H₂biim = 2,2-biimidazole; dinuclear K₂[M₂(acac)₄(-biim)] (M = Cu^II or Zn^II) and tetranuclear K₂[M₄(acac)₈( ₄-biim)] (M = Co^II or Ni^II) complexes have been prepared and characterized by chemical analysis, conductance measurements, i.r., electronic and e.p.r. spectroscopies and by magnetic susceptibility measurements (in the 2–300 K range). Mn^II, Fe^II and Co^II are in a high spin state. The e.p.r. spectra of Cu^II and Mn^II compounds have been recorded.     

Experimental and theoretical study of the charge transport property of 4,4′-N,N′-dicarbazole-biphenyl

The hole and electron mobilities of the amorphous films of the organic semiconductor 4,4′-N,N′-dicarbazole-biphenyl (CBP) at different electric fields were measured through the time of flight (TOF) method. Based on its crystalline structure, the hole and electron mobilities of CBP were calculated. A detailed comparison between experimental and theoretical results is necessary for further understanding its charge transport properties. In order to do this, charge mobilities at zero electric field, μ(0), were deduced from experimental data as a link between experimental and theoretical data. It was found that the electron transport of CBP is less affected by traps compared with its hole transport. This unusual phenomenon can be understood through the distributions of frontier molecular orbitals. We showed that designing materials with frontier molecular orbitals localized at the center of the molecule has the potency to reduce the influence of traps on charge transport and provide new insights into designing high mobility charge transport materials.     

Combination of the Claisen-Schmidt reaction,the Michael addition,and the Hantzsch reaction in the synthesis of 2,6′-bis-aryl-3,4′-bipyridines

Russian Chemical Bulletin - Pyridine-3-carbaldehyde reacted with 1-(aryl)ethan-1-ones to give 1,5-diaryl-3-(pyridin-3-yl)pentane-1,5-diones, which were further converted to...     

Coordination behaviour of 2,2′-bipyridine towards the dichloroacetates of zinc and cadmium

The coordiantion compounds [Zn(C₁₀H₈N₂)(Cl₂HCCOO)(H₂O)₃]⁻·[Zn(C₁₀H₈N₂)(Cl₂HCCOO)₃]⁺ and [Cd(C₁₀H₈N₂)₂(Cl₂CHCOO)₂] were synthesised and characterised by elemental and thermal analysis, IR and UV–VIS spectroscopy, and X-ray crystallography. The complexes are air stable and well-soluble in water. The zinc atoms are five and six coordinated and the cadmium atom is six coordinated. The coordination polyhedra of central atoms can be described as trapezoidal pyramid and octahedron in zinc compound and as rectangular bipyramid strongly distorted towards skew trapezoidal bipyramid in cadmium compound. In both compounds all dichloroacetate groups are monodentate. The bond valences considerations show that all 2,2′-bipyridine molecules are bonded almost 2 times stronger than carboxylate groups. In the structure of zinc compound exist O–H···O hydrogen bonds and in both structures can be found weak C–H···O hydrogen bonds. Additionally, both compounds are pile-stacked by π···π interactions. The IR spectra show typical vibrations for chelating 2,2′-bipyridine molecules and terminal monodentate carboxylate groups. The thermal decomposition studies show zinc compound decomposes in 4 steps and cadmium compound decomposes in 5 steps with formation of oxides as a final products. The ligands decompose gradually, first dichloroacetates and next 2,2′-bipyridine.     

FT-IR study of the conformation and proton acceptor ability of N-tertiobutoxycarbonylsarcosine N′-methylamide and N-tertiobutoxycarbonylsarcosine N′,N′-dimethylacetamide

Two model dipeptides, N-tertiobutoxycarbonylsarcosine N′-methylamide (BSMA) and N-tertiobutoxycarbonylsarcosine N′,N′-dimethylamide (BSDA) are investigated by FT-IR spectrometry. The conformation of BSMA is very sensitive to the environment. In solvents of weak polarity (carbon tetrachloride, cyclohexane), BSMA accomodates the extended and seven-membered ring conformation, but in 1,2-dichloroethane, the C₇ conformers are greatly destabilized. Hydrogen bonding between BSMA or BSDA and phenols is studied in carbon tetrachloride. The thermodynamic data (equilibrium constants and enthalpies of complex formation) show that the BSMA complexes are stronger than the BSDA complexes. The spectroscopic data suggest that for BSMA, complex formation occurs at the O atom of the amide function while for BSDA about 50% of the complexes are formed on the O atom of the urethane group. The differences between the two sarcosine dipeptides are discussed in terms of cooperative and steric effects. It can be concluded that the global polarity of the medium exerts a greater influence on the conformation of the C₇ dipeptides than the specific interactions taking place on a given site of the molecule.     

Thermodynamics of the solvation and phase distributions of 2,2′-dipyridyl in acetonitrile-DMSO-hexane and methanol-DMSO-hexane systems

The Gibbs energies of 2,2′-dipyridyl when transferred from dimethyl sulfoxide to its mixtures with acetonitrile and methanol are determined from the distribution of substance between immiscible phases. It is found that moving from dimethyl sulfoxide to acetonitrile and methanol weakens the solvation of 2,2′-dipyridyl due to a change in the solvation of amino groups and the hydrocarbon substituent, which is reflected in a reduction in the entropy component of the Gibbs energy.     

Preparation of 2,2′-anhydronucleosides: regio- and stereoselective modifications of the base and sugar moieties

2′-Deoxy-2′-iodonucleosides 4–9, obtained from suitably protected furanoid glycals 1 and 2 with different silylated pyrimidine bases, were transformed into the corresponding 2,2′-anhydronucleosides 10–15 with inversion of the configuration at C-2′, by heating in DMF with n-dibutyltin oxide. Regio- and stereospecific opening at C-2′ of the 2,2′-ring in compounds 10, 11, and 12 with sodium azide afforded the related 2′-azido-2′-deoxynucleosides 16, 17 and 18, respectively. Action of sodium hydroxide on 12 caused the regioselective opening of the above-mentioned ring at C-2 with retention of the configuration at C-2′ giving 19. Compound 19 could be transformed straightforwardly into 18 by well-established methodology. On the other hand, compound 15 could be transformed into the related 2′,3′-anhydronucleoside 23 by a regio- and stereoselective addition at N-3–C-2′ of allyl bromide concomitant with 2,2′-ring opening and inversion of the configuration at C-2′ to afford the intermediate 2′-bromo-2′-deoxynucleoside 21, which was subsequently treated with sodium methoxide giving 23.     

Spectroscopic and electrochemical study of dinuclear and mononuclear copper complexes with the bidentate ligand of the 2,2′-diquinoline series

The newly synthesized complex (2) of copper(I) chloride with di-n-hexyl 2,2′-biquinoline-4,4′-dicarboxylate (L) was spectroscopically and electrochemically characterized. The X-ray diffraction study showed that the crystals of complex 2 consist of the dinuclear moieties [L₂Cu¹ ₂(μ-Cl)₂] containing Cu₂(μ-Cl)₂ clusters. Spectrophotometric studies and ESI-mass spec-trometric measurements showed that after the dissolution of complex 2 in acetonitrile (AN) and N-methyl-2-pyrrolidone (NMP), the solution contained not only the dinuclear complexes [L₂Cu¹ ₂(μ-Cl)₂] but also [L₂Cu¹]Cl, [LCu¹Cl(Sol)], and [Cu¹Cl(Sol)] (Sol is the solvent). The electrochemical data also confirm the conclusion that bridged dinuclear chloride complex 2 dissociates both in NMP and AN to form the tetrahedral bis-biquinoline complex [L₂Cu¹]Cl. In solutions of complex 2 in alcohols and _N,_N-dimethylformamide (DMF), only [L₂Cu¹]Cl and [Cu¹Cl(Sol)] are present. In EtOH, AN, and DMF, [Cu¹Cl(Sol)] undergoes disproportionation to [Cu¹¹Cl(Sol)] and Cu⁰.     

Resolution and determination of the absolute configuration of 3,3′,4,4′-tetramethyl-1,1′-diphosphaferrocene-2-carboxaldehyde

Racemic 3,3′,4,4′-tetramethyl-1,1′-diphosphaferrocene-2-carboxaldehyde 1 was resolved via the formation of diastereomeric dioxolanes with (S)-(+)-1-phenyl-1,2-ethanediol. Four stereoisomers were separated by column chromatography. The absolute configuration of one of them (2′′R, 4′′S,1R) was established by X-ray diffraction. Acid hydrolysis of the dioxolanes afforded quantitatively (R)- and (S)-enantiomers of 1. Optical rotatory dispersion (ORD) spectra of both enantiomers are also reported.     

Determination of the rates of formation and hydrolysis of the Schiff bases formed by pyridoxal 5′-phosphate and copolypeptides containing l-lysine

We determined the apparent rate constants of formation (k₁) and hydrolysis (k₂) of the Schiff bases formed between pyridoxal 5′-phosphate (PLP) and l-lysine and l-alanine copolymers of different compositions, as well as those formed between PLP and l-lysine and l-glutamic acid copolymers, at various pH values, a temperature of 25 °C and an ionic strength of 0.1 M. The k₁ values obtained in neutral and acidic media were independent of the copolymer composition. The efficiency of the intramolecular acid catalysis for the formation of the Schiff bases was found to be somewhat higher than that of PLP—primary amine systems (the slope of the Brøwted plot was α=0.77). The most stable of the Schiff bases studied was that with a protonated imine nitrogen and phosphate group and a unprotonated pyridine nitrogen.     

Physicochemical studies of the structure of N,N′-dinitrourea and its salts

The properties and behavior of dinitrourea and its potassium and dipotassium salts in different solvents have been studied by IR and UV spectroscopy. In different media, dinitrourea can exist in several tautomeric forms. An XRD study of the potassium and dipotassium salts of dinitrourea revealed a tendency toward equalization of the bond lengths of the C-N⁻-NO₂ fragments compared with those of C-NH-NO₂, which agrees with the results of quantum-chemical calculations.     

Comparative study of the electrosynthesis and characterization of films made from 1,1′-binaphthyl and 2-methoxynaphthalene

Oligomers of 2-methoxynaphthalene and 1,1-binaphthyl were electrochemically synthesized by cyclic voltammetry (CV) in 0.1 M tetrabutylammonium hexafluorophosphate–nitrobenzene (TBAPF₆–NB). The redox characterization of the films was studied in monomer-free 0.1 M TBAPF₆–NB and 0.1 M tetrabutylammonium hexafluorophosphate–acetonitrile (TBAPF₆–ACN) solutions. The electrochemical response from the anodic charging (p-doping) of an oligo(1,1-binaphthyl) film in both solvents consists of a continously increasing current without a well-defined oxidation peak. Upon discharging the film a distinct reduction peak can be seen. The p-doping response of an oligo(2-methoxynaphthalene) film in both solvents consists of a prepeak followed by a plateau until the new electrochemical process starts. On the reverse scan two poorly resolved reduction peaks which merge into a broad cathodic peak as the scan rate increases can be observed. The cathodic charging and discharging (n-doping) response of 2-methoxynaphthalene film in 0.1 M TBAPF₆–ACN consists of a broad and well-defined redox peak. The structures of the film were studied by Raman and Fourier transform infrared spectroscopy (FTIR). Both techniques provide complementary vibrational information on the coupling of the starting materials studied. The morphologies of the electrosynthesized films were studied by scanning electron microscopy (SEM). The influence of the two substituents, the methoxy and naphthyl groups, on the electrosynthesis properties of the naphthalene molecule was studied.     

Hydrothermal and Solvothermal Synthesis of the Complex Fluoride α′-SrAIF5

The complex fluoride α′-SrAlF5 has been synthesized through hydrothermal and solvothermal methods under mild conditions.The effects of the molar ratio of starting materials,temperature,reaction time and solvents on the synthesis of α′-SrAlF5 were discussed.The final products were characterized by XRD and SEM.The rod-like shape of α′-SrAlF5 is shown in SEM images.