Mechanistic Insights into the Formation of 1-Alkylidene/Arylidene-1,2,4-triazolinium Salts: A Combined NMR/Density Functional Theory Approach.

In a recent report on the synthetic approach to the novel substance class of 1-alkylidene/arylidene-1,2,4-triazolinium salts, a reaction mechanism suggesting a regioselective outcome was proposed. This hypothesis was tested via a combined NMR and density functional theory (DFT) approach. To this end, three experiments with 13C-labeled carbonyl reactants were monitored in situ by solution-state NMR. In one experiment, an intermediate as described in the former mechanistic proposal was observed. However, incorporation of 13C isotope labels into multiple sites of the heterocycle could not be reconciled with the "regioselective mechanism". It was found that an unproductive reaction pathway can lead to 13C scrambling, along with metathetical carbonyl exchange. According to DFT calculations, the concurring reaction pathways are connected via a thermodynamically controlled cyclic 1,3-oxazetidine intermediate. The obtained insights were applied in a synthetic study including aliphatic ketones and para-substituted benzaldehydes. The mechanistic peculiarities set the potential synthetic scope of the novel reaction type.

A Fluoroponytailed NHC-Silver Complex Formed from Vinylimidazolium/AgNO3 under Aqueous-Ammoniacal Conditions.

3-(1H,1H,2H,2H-Perfluorooctyl)-1-vinylimidazolium chloride [2126844-17-3], a strong fluorosurfactant with remarkably high solubility in water, was expediently converted into the respective doubly NHC-complexed silver salt with nitrate as counter ion in quantitative yield. Due to its vinyl substituents, [bis(3-(1H,1H,2H,2H-perfluorooctyl)-1-vinylimidazol-2-ylidene)silver(I)] nitrate, Ag(FNHC)2NO3, represents a polymerizable N-heterocyclic carbene transfer reagent, thus potentially offering simple and robust access to coordination polymers with crosslinking metal bridges. The compound was characterized by infrared and NMR spectroscopy, mass spectrometry as well as elemental analysis, and supplemented by X-ray single-crystal structure determination. It crystallizes in the monoclinic crystal system in the space group P21/c. With 173.3°, the geometry of the Ag-carbene bridge deviates slightly from linearity. The disordered perfluoroalkyl side chains exhibit a helical conformation.

Highly Electrophilic, Catalytically Active and Redox-Responsive Cobaltoceniumyl and Ferrocenyl Triazolylidene Coinage Metal Complexes.

A convenient access to a triad of triazoles with ferrocenyl and cobaltoceniumyl substituents is reported. N-Alkylation, deprotonation and metalation with CuI /AgI /AuI synthons affords the heteroleptic triazolylidene complexes. Due to the combination of neutral, electron-donating ferrocenyl substituents and cationic, strongly electron-withdrawing cobaltocenium substituents, the mesoionic carbene (MIC) ligands of these complexes are electronically interesting "push-pull", "pull-push" and "pull-pull" metalloligands with further switchable redox states based on their fully reversible FeII /FeIII , (ferrocene/ferrocenium) and CoIII /CoII , (cobaltocenium/cobaltocene) redox couples. These are the first examples of metal complexes of (di)cationic NHC ligands based on cobaltoceniumyl substituents. DFT calculated Tolman electronic parameter (TEP) of the new MIC ligands, show these metalloligands to be extremely electron-poor NHCs with properties unmatched in other carbene chemistry. Utilization of these multimetallic electronically tunable compounds in catalytic oxazoline synthesis and in antitumor studies are presented. Remarkably, 1 mol % of the AuI complex with the dicationic MIC ligand displays full catalytic conversion, without the need for any other additives, in less than 2 hours at ambient temperatures. These results thus firmly establish these new classes of cobaltoceniumyl based (di)cationic MIC ligands as prominent players in several branches of chemistry.

Synthesis of enantiopure antiobesity drug lorcaserin.

Acylation of enantiomerically pure (R)-2-(3-chlorophenyl)propan-1-amine using chloroacetyl chloride, followed by borane reduction and aluminum chloride catalyzed cyclization yielded enantiopure lorcaserin.

Structural Redetermination and Photoluminescence Properties of the Niobium Oxyphosphate (NbO)2P4O13.

The structure of (NbO)2P4O13 was solved and refined based on new single-crystal diffraction data revealing considerably more complexity than previously described. (NbO)2P4O13 crystallizes in the triclinic space group P1̅ with Z = 6. The lattice parameters determined at room temperature are a = 1066.42(4) pm, b = 1083.09(4) pm, c = 1560.46(5) pm, α = 98.55(1)°, ß = 95.57(1)°, γ = 102.92(1)°, and V = 1.7213(2) nm3. The superstructure contains 64 unique atoms including two disordered semioccupied oxygen positions. An unusual 180° bond angle between two [P4O13]6- groups was refined to form half-occupied, split positions in agreement with previous reports. The IR and Raman spectra reflect the appearance of overlapping bands assignable to specific group vibrations as well as P-O-P linkages present in the [P4O13]6- entities. Investigation of the powdered product concerning its photoluminescence properties revealed an excitability in the UV at 270 nm assigned to O2p-Nb4d charge transfer transitions. A resulting broad-band emission with the maximum in the visible region at 455 nm was determined.

Crystal structure of 4-amino-1-benzyl-1,2,4-triazolin-5-one.

The title compound, C9H10N4O, was obtained unintentionally by hydrolysis of 4-amino-1-benzyl-5-methyl-sulfanyl-1,2,4-triazolium tetra-fluoro-borate in the presence of sodium azide. In the crystal, alternating layers of polar amino-triazolinone and apolar benzene moieties are observed. N-H⋯O hydrogen bonds between the amino and carbonyl groups form infinite chains along [010]. These infinite chains are linked by additional C-H⋯O contacts.

Separation of hemicellulose and cellulose from wood pulp by means of ionic liquid/cosolvent systems.

Pulp of high cellulose content, also known as dissolving pulp, is needed for many purposes, including the production of cellulosic fibers and films. Paper-grade pulp, which is rich in hemicellulose, could be a cheap source but must be refined. Hitherto, hemicellulose extraction procedures suffered from a loss of cellulose and the non-recoverability of unaltered hemicelluloses. Herein, an environmentally benign fractionation concept is presented, using mixtures of a cosolvent (water, ethanol, or acetone) and the cellulose dissolving ionic liquid 1-ethyl-3-methylimidazolium acetate (EMIM OAc). This cosolvent addition was monitored using Kamlet-Taft parameters, and appropriate stirring conditions (3 h at 60 °C) were maintained. This allowed the fractionation of a paper-grade kraft pulp into a separated cellulose and a regenerated hemicellulose fraction. Both of these exhibited high levels of purity, without any yield losses or depolymerization. Thus, this process represents an ecologically and economically efficient alternative in producing dissolving pulp of highest purity.

Iclaprim mesylate displaying a hydrogen-bonded mol-ecular tape.

The title compound, 2,6-di-amino-5-[(2-cyclo-propyl-7,8-dimeth-oxy-2H-1-benzo-pyran-5-yl)meth-yl]pyrimidin-1-ium methane-sulfonate, C19H23N4O3 +·CH3O3S-, is a salt made up from a protonated iclaprim mol-ecule and a mesylate anion. The pyrimidine and chromene units of the iclaprim mol-ecule form an orthogonal arrangement [inter-planar angle of 89.67 (6)°], and the 3-nitro-gen position of the pyrimidine ring is protonated. Four distinct N-H⋯O inter-actions and an additional N-H⋯N hydrogen bond connect iclaprim and mesylate mol-ecules to one another, resulting in an infinite hydrogen-bonded mol-ecular tape structure. The central section of the tape is formed by a sequence of fused hydrogen-bonded rings involving four distinct ring types.

Dialkyl phosphate-related ionic liquids as selective solvents for xylan.

Herein we describe a possibility of selective dissolution of xylan, the most important type of hemicellulose, from Eucalyptus globulus kraft pulp using ionic liquids (ILs). On the basis of the IL 1-butyl-3-methylimidazolium dimethyl phosphate, which is well-known to dissolve pulp, the phosphate anion was modified by substituting one oxygen atom for sulfur and selenium, respectively. This alteration reduces the hydrogen bond basicity of the IL and therefore prevents dissolution of cellulose fibers, whereas the less ordered xylan is still dissolved. (1)H NMR spectra of model solutions and Kamlet-Taft parameters were used to quantify the solvent polarity and hydrogen bond acceptor properties of the ILs. These parameters have been correlated to their ability to dissolve xylan and cellulose, which was monitored by (13)C NMR spectroscopy. It was found that the selectivity for xylan dissolution increases to a certain extent with decreasing hydrogen-bond-accepting ability of anions of the ILs.

Mössbauer spectroscopy and X-ray diffraction study of Fe-labeled tetrachloroferrate(III)-based magnetic ionic liquids.

Four (57)Fe-labeled tetrachloroferrates(III) of organic cations (1-butyl-3-methylimidazolium, 1-allyl-3-methylimidazolium, 1-methyl-1-propylpyrrolidinium, tetraphenylphosphonium) were examined by temperature-dependent Mössbauer spectroscopy. The hyperfine and dynamic parameters of the iron(III) site were determined. Single crystal X-ray diffraction data of [Ph(4)P][FeCl(4)] were collected at four temperatures (295, 223, 173, and 123 K), and the dynamics of the iron atom inferred from the Mössbauer data and the single crystal U(i,j) parameters have been compared.

Synthesis and crystal structures of two 1,3-di(alk-yloxy)-2-(methyl-sulfan-yl)imidazolium tetra-fluorido-borates.

Two salts were prepared by methyl-ation of the respective imidazoline-2-thione at the sulfur atom, using Meerwein's salt (tri-methyl-oxonium tetra-fluorido-borate) in CH2Cl2. 1,3-Dimeth-oxy-2-(methyl-sulfan-yl)imidazolium tetra-fluorido-borate (1), C6H11N2O2S+·BF4 -, displays a syn conformation of its two meth-oxy groups relative to each other whereas the two benz-yloxy groups present in 1,3-dibenz-yloxy-2-(methyl-sulfan-yl)imidazolium tetra-fluorido-borate (2), C18H19N2O2S+·BF4 -, adopt an anti conformation. In the mol-ecules of 1 and 2, the methyl-sulfanyl group is rotated out of the plane of the respective heterocyclic ring. In both crystal structures, inter-molecular inter-actions are dominated by C-H⋯F-B contacts, leading to three-dimensional networks. The tetra-fluorido-borate counter-ion of 2 is disordered over three orientations (occupancy ratio 0.42:0.34:0.24), which are related by rotation about one of the B-F bonds.

Synthesis and crystal structures of 2-bromo-1,3-di-methyl-imidazolium iodides.

Attempts at direct bromination of 1,3-di-methyl-imidazolium salts were futile. The title compounds, 2-bromo-1,3-di-methyl-imidazolium iodide chloro-form 0.33-solvate, C5H8BrN2+·I-·0.33CHCl3, 2-bromo-1,3-di-methyl-imidazolium iodide di-chloro-methane hemisolvate, C5H8BrN2+·I-·0.5CH2Cl2, and 2-bromo-1,3-di-methyl-imidazolium iodide hemi(diiodide), C5H8BrN2+·I-·0.5I2, were obtained by methyl-ation of 2-bromo-1-methyl-imidazole. They crystallized as CHCl3, CH2Cl2 or I2 solvates/adducts. The Br atom acts as a σ-hole to accept short C-Br⋯I inter-actions. C-H⋯I hydrogen bonds are observed in each structure.

An innovative monolithic zwitterionic stationary phase for the separation of phenolic acids in coffee bean extracts by capillary electrochromatography.

A methacrylate based monolith, containing the innovative zwitterionic monomer (3-allyl-1-imidazol)propane sulfonate, was prepared in 100 µm I.D. silica capillaries by UV initiated photo-polymerization. Composition of the porogen, i.e. a mixture of 1-propanol, 1,4 butanediol and water, was of great importance to obtain a homogeneous monolith with satisfactory permeability and good electrochromatographic performance. Morphology of the stationary phase was studied in Scanning Electron Microscopy and IR experiments, which revealed a good attachment to the capillary wall, flowthrough-pores in the range of 0.5-2 µm, and a continuous monolithic structure. The developed material was well suited for the analysis of six common phenolic acids (salicylic, cinnamic, syringic, rosmarinic, caffeic and chlorogenic acid) by CEC. Their separation was possible in less than 8 min with a mobile phase comprising a 12 mM aqueous ammonium acetate solution with pH 8.5 and acetonitrile, at an applied voltage of - 20 kV. The developed method was validated (R2 ≥ 0.995; LOD ≤ 3.9 µg mL-1, except for salicylic acid; recovery rates from 94 to 104%) and successfully used for the determination of phenolic acids in Coffea arabica samples. All of them contained cinnamic, syringic and caffeic acid, however only in unroasted coffee beans chlorogenic acid (0.06%) was found. The quantitative results were in good agreement to reported literature data.

(E)-2,6-Di-bromo-4-{2-[1-(1H,1H,2H,2H-perfluoro-oct-yl)pyridinium-4-yl]ethen-yl}phenolate methanol disolvate, a fluoro-ponytailed solvatochromic dye.

The title compound, C21H12Br2F13NO·2CH3OH, was obtained by condensation of 4-methyl-1-(1H,1H,2H,2H-perfluoro-oct-yl)pyridinium iodide and 3,5-di-bromo-4-hy-droxy-benzaldehyde, followed by deprotonation. It crystallizes as a methanol disolvate and exhibits short O-H⋯O hydrogen bonds and a disordered perfluoro-alkyl chain [occupancy ratio 0.538 (7):0.462 (7)]. Significant π-π stacking inter-actions are observed between the benzene and pyridine rings of neighbouring mol-ecules along the b-axis direction.

The Hydrogen Bonded Structures of Two 5-Bromobarbituric Acids and Analysis of Unequal C5-X and C5-X' Bond Lengths (X = X' = F, Cl, Br or Me) in 5,5-Disubstituted Barbituric Acids.

The crystal structure of the methanol hemisolvate of 5,5-dibromobarbituric acid (1MH) displays an H-bonded layer structure which is based on N-H⋯O=C, N-H⋯O(MeOH) and (MeOH)O-H⋯O interactions. The barbiturate molecules form an H-bonded substructure which has the fes topology. 5,5'-Methanediylbis(5-bromobarbituric acid) 2, obtained from a solution of 5,5-dibromobarbituric acid in nitromethane, displays a N-H⋯O=C bonded framework of the sxd type. The conformation of the pyridmidine ring and the lengths of the ring substituent bonds C5-X and C5-X' in crystal forms of 5,5-dibromobarbituric acid and three closely related analogues (X = X' = Br, Cl, F, Me) have been investigated. In each case, a conformation close to a C5-endo envelope is correlated with a significant lengthening of the axial C5-X' in comparison to the equatorial C5-X bond. Isolated molecule geometry optimizations at different levels of theory confirm that the C5-endo envelope is the global conformational energy minimum of 5,5-dihalogenbarbituric acids. The relative lengthening of the axial bond is therefore interpreted as an inherent feature of the preferred envelope conformation of the pyrimidine ring, which minimizes repulsive interactions between the axial substituent and pyrimidine ring atoms.

Crystal structure of 1-[2-(di-ethyl-aza-n-ium-yl)eth-yl]-3-methyl-imidazolium tetra-chlorido-cuprate(II).

The title compound, (C10H21N3)[CuCl4], is composed of one 1-[2-(di-ethyl-aza-nium-yl)eth-yl]-3-methyl-imidazolium dication and a tetra-chlorido-cuprate(II) dianion. The anion adopts a distorted tetra-hedral geometry. Bifurcated interionic N-H⋯Cl hydrogen bonds and several C-H⋯Cl contacts are observed, leading to a layer-like arrangement of the components parallel to (100).

Crystal structure of bis-(1,3-di-meth-oxy-imidazolin-2-yl-idene)silver(I) hexa-fluorido-phosphate, N-heterocyclic carbene (NHC) complex.

The title salt, [Ag(C5H8N2O2)2]PF6, was obtained by deprotonation and metalation of 1,3-di-meth-oxy-imidazolium hexa-fluorido-phosphate using silver(I) oxide in methanol. The C-Ag-C angle in the cation is 178.1 (2)°, and the N-C-N angles are 101.1 (4) and 100.5 (4)°. The meth-oxy groups adopt an anti conformation. In the crystal, anions (A) are sandwiched between cations (C) in a layered arrangement {C…A…C} n stacked along [001]. Within a C…A…C layer, the hexafluoridophosphate anions accept several C-H⋯F hydrogen bonds from the cationic complex.

Crystal structure of 1-(1-methyl-1H-imidazol-2-yl)-4-phenyl-1H-1,2,3-triazole dihydrate.

The title compound, C12H11N5·2H2O, which crystallizes as a dihydrate, was obtained by Cu(I)-catalysed azide-alkyne cyclo-addition from 2-azido-1-methyl-imidazole and phenyl-ethyne. The dihedral angles between the central triazole ring (r.m.s. deviation = 0.004 Å) and the pendant imidazole (r.m.s. deviation = 0.006 Å) and phenyl rings are 12.3 (2) and 2.54 (19)°, respectively. In the crystal, the water mol-ecules are connected into [010] chains by O-H⋯O hydrogen bonds, while O-H⋯N hydrogen bonds connect the water mol-ecules to the organic mol-ecules, generating corrugated (100) sheets.

Crystal structure of 3-bromo-4-di-methyl-amino-1-methyl-1,2,4-triazol-5(4H)-one.

The title compound, C5H9BrN4O, was obtained as a minor by-product in the synthesis of 4-di-methyl-amino-1-methyl-1,2,4-triazolin-5-one. Except for the methyl groups of the 4-dimethylamino moiety, all the non-H atoms lie on a crystallographic mirror plane." In the crystal, the mol-ecules are linked by C-Br⋯O=C inter-actions [Br⋯O = 2.877 (2) Å, C-Br⋯O = 174.6 (1)°] into infinite chains in the c-axis direction.

Crystal structure of 3-bromo-2-hy-droxy-benzoic acid.

Mutual carbox-yl-carboxyl O-H⋯O hydrogen bonds link the mol-ecules of the title compound, C7H5BrO3, into centrosymmetric dimers which display a central R 2 (2)(8) ring motif. In addition, there is an intra-molecular hydrox-yl-carboxyl O-H⋯O inter-action present. A comparison with the crystal structures of 59 other substituted derivatives of salicylic acid shows that both the centrosymmetric carbox-yl-carboxyl O-H⋯O dimer and the stacking mode of mol-ecules along the short a axis observed in the title structure are frequent packing motifs in this set.