Synthesis of a new zwitterionic cyclopentadienyl-imidazolium compound and isolation of the 3,3′-(trans-3,5-cyclopentenyl)di(1-tert-butylimidazolium)bromide intermediate

The new zwitterionic compound 1-tert-butylimidazolium-cyclopentadienylide, shown to have a polar ground state and a non-polar fulvene-like excited state, has been synthesised and the intermediate 3,3′-(trans-3,5-cyclopentenyl)di(1-tert-butylimidazolium)bromide isolated and structurally characterised.     

New carboxy-functionalized terpyridines as precursors for zwitterionic ruthenium complexes for polymer-based solar cells

New carboxy-terpyridines selectively functionalized at the 4-, 4′- and 4″-positions were prepared in a three-step procedure with good yields using the Kröhnke reaction followed by saponification. Their complexation with ruthenium led to symmetric and unsymmetric terpyridinyl zwitterionic complexes.     

Two-step liquid phase microextraction combined with capillary electrophoresis: A new approach to simultaneous determination of basic and zwitterionic compounds

In this work, two-step hollow fiber-based liquid-phase microextraction procedure was evaluated for extraction of the zwitterionic cetirizine (CTZ) and basic hydroxyzine (HZ) in human plasma. In the first step of extraction, the pH of sample was adjusted at 5.0 in order to promote liquid-phase microextraction of the zwitterionic CTZ. In the second step, the pH of sample was increased up to 11.0 for extraction of basic HZ. In this procedure, the extraction times for the first and the second steps were 30 and 20 min, respectively. Owing to the high ratio between the volumes of donor phase and acceptor phase, CTZ and HZ were enriched by factors of 280 and 355, respectively. The linearity of the analytical method was investigated for both compounds in the range of 10-500 ng mL(-1) (R(2) > 0.999). Limit of quantification (S/N = 10) for CTZ and HZ was 10 ng mL(-1) , while the limit of detection was 3 ng mL(-1) for both compounds at a signal to noise ratio of 3:1. Intraday and interday relative standard deviations (RSDs, n = 6) were in the range of 6.5-16.2%. This procedure enabled CTZ and HZ to be analyzed simultaneously by capillary electrophoresis.     

Control of symmetry in active cationic ansa-zirconocene species: catalyst preparation, characterization and ethylene-norbornene copolymerization

New bis-hydrocarbyl complexes of methylene bridged ansa-metallocenes [H₂C(C₅Me₂H₂)₂]ZrR₂ {R = Me (1), CH₂Ph (2), CH₂SiMe₃ (3), Ph (4)} have been prepared. They form catalytically active intermediates with borane or borate depending on solvent and Zr-R group. Specifically, [H₂C(Me₂C₅H₂)₂]Zr(CH₂Ph)₂ (2) produced an ion pair upon treatment with B(C₆F₅)₃ whereas [H₂C(Me₂C₅H₂)₂]Zr(CH₂SiMe₃)₂ (3) produced a zwitterionic species, identified by ¹H, ¹³C, and ¹⁹F NMR spectroscopy. Copolymerization of ethylene and norbornene for the metallocene dichloride/MAO and bis-hydrocarbyl complex/borate systems was compared.     

Application of pH-responsive poly(2-dimethyl-aminoethylmethacrylate)-block-poly(acrylic acid) coatings for the open-tubular capillary electrochromatographic analysis of acidic and basic compounds

A new type of stimuli-responsive polymeric (SRP) coating has been prepared for use in open tubular capillary electrochromatography (OT-CEC), by grafting poly(2-dimethylaminoethylmethacrylate)-block-poly(acrylic acid) (PDMAEMA-b-PAA) as a Y-shaped block copolymer with two dissimilar chain compositions onto the inner walls of aminopropyl-modified silica capillaries. The grafting process introduced weakly charged functional groups from the PAA and PDMAEMA, enabling the generation of electroendosmotic flow with magnitude and direction adjustable by changing the pH of the running buffer electrolyte. This stimuli-responsive PDMAEMA-b-PAA block copolymer was found to provide excellent resolution of various acidic and basic compounds, leading to efficient analyte separation. When operated in the OT-CEC mode, separation selectivities could be readily manipulated via differential contributions from chromatographic and electrophoretic mechanisms, simply by changing the pH or the ionic strength of the running buffer electrolyte.     

Novel regio- and stereo-selectivity: synthesis of dihydropyrrolo[1,2-f]phenanthridines via isocyanide-based multicomponent reaction

The novel one-pot three-component reactions of the zwitterions generated in situ from three isocyanides and 2-arylidenemalononitriles with phenanthridine via 1,3-dipolar cycloaddition are described. The reactions afforded the corresponding dihydropyrrolo[1,2-f]phenanthridine derivatives in good yields without using any catalyst and activation. The stereochemistry of the final products was confirmed by single-crystal X-ray diffraction analysis.     

Synthesis and characterization of dinuclear monohydro sesquifulvalene complexes with potential NLO properties

E-1-(1″-hydroxycarbonylferrocen-1′-yl)-2-(cycloheptatrienyl)ethene (4) was synthesized by using selective transmetallation reactions. Reaction of 4 with [Cp*Ru(CH₃CN)₃](PF₆) revealed the vinylogue monohydro sesquifulvalene complex E-1-(1″-hydroxycarbonylferrocen-1′-yl)-2-{(1?-6?-η-cyclohepta-1?,3?,5?-trien-1?-yl)(η⁵-pentamethylcyclopentadienyl)ruthenium(II)}ethene hexafluorophosphate (5). X-ray structure analysis demonstrates that complex 5 crystallizes in the triclinic space group , which forms discrete dimers via two hydrogen bonds between the carboxylic functions. Reaction of complex 5 with triethylamine or NaHCO₃ generated a new organometallic zwitterion E-1-(1″-oxycarbonylferrocen-1′-yl)-2-{(1?-6?-η-cyclohepta-1?,3?,5?-trien-1?-yl)(η⁵-pentamethylcyclopentadienyl)ruthenium(II)}ethene (6), which was characterized by UV, IR, and NMR spectra.     

Syntheses and crystal structure studies of two zinc complexes of enoxacin

Two zinc complexes of enoxacin were synthesized and their crystal structures were determined. Compound 1, [Zn(H-Eno) · Cl₂] · 3H₂O (H-Eno = Enoxacin), crystallizes in the triclinic system, space group P 1, with lattice parameters a = 8.7731(12), b = 9.4976(14), and c = 13.2033(19) Å, α = 86.319(7)°, β = 71.912(7)°, and γ = 80.604(7)°, V = 1031.6(3) ų, Z = 2, D _Calcd = 1.631 Mg m^?3; compound 2, [Zn(H-Eno) · (H₂O)₂] · 2NO₃, also crystallizes in the triclinic system, space group P 1, with lattice parameters a = 8.751(2), b = 9.014(2), and c = 12.594(3) Å, α = 92.277(14)°, β = 109.867(12)°, and γ = 111.469(12)°, V = 854.1(3) ų, Z = 1, D _Calcd = 1.684 Mg m^?3.     

Reactions of 1,1-bis(dimethylamino)-1,3-butadiene with olefins – (4 + 2) cycloadditions and zwitterion formation

1,1-Bis(dimethylamino)-1,3-butadiene ( 1 ) as a strong donor diene (E_1/2 = 0.03 V vs. SCE, 1st IP_v = 6.94 eV) is treated with acrylonitrile, dimethyl dicyanofumarate, and tetracyanoethylene. Cycloaddition with acrylonitrile is slow and requires elevated temperatures at which elimination of dimethylamine with formation of 1-cyano-2-(dimethylamino)-1,3-cyclohexadiene occurs. The reaction of 1 with TCNE at −40°C in acetonitrile is very fast and leads to the zwitterion 5 . At T ⩾ −20°C, 5 eliminates hydrogen cyanide to give a highly colored (λ_max = 489 nm, lgϵ = 4.716) merocyanine. A zwitterion 9 generated from 1 and dimethyl dicyanofumarate can be isolated in crystalline form. The structural analysis shows that the zwitterions are produced by attack of the olefin at the antiperiplanar conformation of 1 . Both zwitterions which can be trapped as crystalline picrates cannot be converted to cycloadducts. These results suggest that cycloaddition is observed if zwitterion formation becomes energetically unfavorable.     

Pyrazino-tetracyanonaphthoquinodimethanes: sterically deformed electron acceptors affording zwitterionic radicals

The X-ray analyses of the title electron acceptors (1) revealed their butterfly-shaped deformed geometry, which is not affected by the pyridyl group attached at 2-position of the pyrazino-TCNNQ skeleton. Small differences between the first and second reduction potentials (ca. 0.1 V) in pyrazino-TCNNQs show that their anion radicals (1⁻) are prone to disproportionate into the neutral (1) and dianionic (1²⁻) species. The thermodynamically unstable anion radical species based on the pyrazino-TCNNQ skeleton could be isolated as inner salts upon electrochemical reduction of the derivatives having an N-methylpyridinium moiety at 2-position (2⁺). The zwitterionic open-shell species (2) constitute a novel class of radicals that exhibit semiconducting behavior as a single component thanks to the high electrochemical amphotericity.