A novel composite Nafion membrane for direct alcohol fuel cells

Trifluoromethanesulfonic acid or triflate acid, chemical formula CF₃SO₃H, is regarded as one of the strongest acids and resembles Nafion^® in structure. Erbium triflate, a lanthanum salt of triflate, is thermally stable. This paper reports data on the formation of membranes by the fixation of erbium triflate salts (ErTfO) into the Nafion structure. Five different loadings of ErTfO were used to fabricate ErTfO/Nafion composite membranes and these were characterized, extensively for possible use in direct alcohol fuel cells. The membranes were characterized using XRD, TGA, FTIR, and for mechanical strength, water uptake, ion exchange capacity, alcohol uptake, swelling, proton conductivity, alcohol permeability and oxygen stability. The ErTfO/Nafion composite membranes reduced alcohol permeability by 77–80%. The proton conductivity of 3% ErTfO/Nafion composite membranes was 38% higher than that of a pure cast Nafion membrane. The oxygen stability of the ErTfO/Nafion composite membranes was higher than pure cast Nafion. However, the mechanical strength of 7% and 9% ErTfO/Nafion was lower than that of pure cast Nafion. The composite membrane was chemically stable and has potential for use in direct alcohol fuel cells.     

Metal triflimide as a Lewis acid catalyst for Biginelli reactions in water

Metal triflimides such as Ni(NTf₂)₂, Cu(NTf₂)₂ and Yb(NTf₂)₃ catalyzed the Biginelli reaction to afford 3,4-dihydropyrimidin-2(1H)-ones more efficiently in pure water at room temperature than did corresponding metal triflate salts.     

Steric effects in palladium-catalysed amination of aryl triflates and nonaflates with the primary amines PhCH(R)NH2 (R=H, Me)

A systematic study of the effects of aryl triflate and nonaflate structure on the yield of amination with the primary amines PhCH(R)NH₂ (R=H, Me) under palladium catalysis has been carried out. High throughput screening indicated that a catalyst composed of X-Phos/Pd₂(dba)₃/1,4-dioxane was optimal based on a model reaction of Ar(OR_f) [R_f=Tf (SO₂CF₃), Nf (SO₂(CF₂)₃CF₃)] with PhCH₂NH₂. Comparisons of the reactivity of various ArOTf and ArONf [Ar=4-MePh, 2-naphthyl, 1-naphthyl, 2-PhC₆H₄] indicated that both ortho substitution in the aryl electrophile and at the α-position on the amine are detrimental to the coupling particularly when they occur in combination. Despite being formally a monodentate ligand use of X-Phos leads to only small degrees of racemisation when using (R)-PhCH(Me)NH₂ (typically resulting in a reduction from 97 to 86-94% ee for the amine stereocentre).     

Facile synthesis of enantiomerically pure tert-butyl(methyl)phenylsilanes

A method for the preparation of both enantiomers of tert-butyl(methyl)phenylsilane 2 is presented. Racemic tert-butyl(methyl)phenylsilyl chloride 3 was allowed to react with (R)-(−)-2-amino-1-butanol 4 to give hydrochloride 5. Diastereomer separation via treatment of the respective free amine 6 with 0.5 mol equivalent of HCl in hexane-2-propanol yielded crystalline diastereomerically pure hydrochloride (R)Si-5. The corresponding free amine (R)Si-6 was reduced with LiAlH₄ to give (S)-2. The mother liquors obtained after separation of (R)Si-5 on treatment with oxalic acid provided a crystalline salt that eventually afforded (R)-2. The optical purity of (S)-2 (98% ee) was documented by its reaction (hydrosilylation) with propargylic alcohol derivative 10 and HPLC analysis of product 11 using a chiral column.     

Optically pure trans-2,3-disubstituted N-sulfinyl aziridines. Regio- and stereoselective opening mediated by the sulfinyl group

A new entry to optically pure trans-2,3-disubstituted N-sulfinyl aziridines starting from 1,2-aminosulfides, involving formation of a sulfonium salt intermediate followed by intramolecular nucleophilic attack by the sulfinamide nitrogen atom, is reported. The regio- and stereoselective opening of the aziridine ring can be achieved by anchimeric assistance of the sulfinyl group.     

Pyridylidene‐Mediated Dihydrogen Activation Coupled with Catalytic Imine Reduction

In recent years, dihydrogen activation at non‐metallic centers has received increasing attention. A system in which dihydrogen is trapped by a pyridylidene intermediate that is generated from a pyridinium salt and a base is now reported. The dihydropyridine formed in this process can act as reducing agent towards organic electrophiles. By coupling the hydrogen‐activation step with subsequent hydride transfer from the dihydropyridine to an imine, a catalytic process was established. Treatment of the N‐phenylimine of phenyl trifluoromethyl ketone with 5–20 mol % of N‐mesityl‐3,5‐bis(2,6‐dimethylphenyl)pyridinium triflate and 0.3–1.0 equivalents of LiN(SiMe₃)₂ under 50 bar of hydrogen gas resulted in high conversion into the corresponding amine.     

Silver(I) and copper(I) complexes with ferrocenyl ligands bearing imidazole or pyridyl substituents

The reactions between five ferrocenyl derivatives containing both a CO and at least an imidazole or pyridine nitrogen atom and AgPF₆, AgOTf, or [Cu(NCCH₃)₄]PF₆ precursors were studied. The ligand {[bis(2-pyridyl)amino]carbonyl}ferrocene (L3), derived from (2-pyridyl)amine, favored tetrahedral coordination of Ag⁺ (with two ligands) and of Cu⁺ (with two acetonitrile ligands left from the precursor). In all the other ligands, both metal centers coordinated linearly to two ligands, preferring the imidazole or pyridinic nitrogen to other nitrogen atoms (amine) or oxygen donors.When the counter anions were triflate, the crystal structure showed a dimerization of the complex, with the ferrocenyl moieties occupying cis positions, by means of a weak Ag?Ag interaction. This was shown experimentally in the crystal structure of complex [Ag(L1)₂]OTf (L1 = ferrocenyl imidazole) and in the presence of peaks corresponding to {Ag₂(L2)₃(OTf)}⁺ and {Ag₂(L2)₄(OTf)}⁺ in the mass spectra of [Ag(L2)₂]OTf (L2 = ferrocenyl benzimidazole). In all complexes containing PF₆, there was no evidence for dimerization. Indeed, in the crystal structure of [Ag(L2)₂]PF₆, the ferrocenyl moieties occupy trans positions and the metal centers are far from each other. DFT calculations showed that the energy of the cis and trans conformers is practically the same and the balance of crystal packing forces leads to dimerization when triflate is present.     

Vibrational spectroscopic and ab initio molecular orbital studies of the normal and 13C-labelled trifluoromethanesulfonate anion

Infrared and Raman spectra of both normal and ¹³C-labelled tetrabutylammonium trifluoromethanesulfonate (triflate) [Bu₄N·CF₃SO₃] and mercury triflate Hg(CF₃SO₃)₂ were recorded at room temperature. The observed isotopic frequency shifts and bandwidths in the vibrational spectra of the triflate anion were taken into account in the assignments of the vibrational modes of the triflate anion. These assignments were supported by ab initio Hartree—Fock self-consistent field (HF-SCF) calculations of vibrational frequencies and normal modes for the triflate anion.     

Complexes triflates de l’uranium

Uranium triflate complexes. We review here the different preparations of uranium triflates that we have developed in the course of these last years in our laboratory. Protonation of 〚U〛–R and 〚U〛–NR₂ (R = alkyl) bonds with pyridinium triflate constitutes a general and efficient route towards triflate complexes. This method is very suitable for the preparation of organometallic compounds such as U(Cp)₃(OTf), U(Cp)₂(OTf)₂(py), U(Cp*)₂(OTf)₂, and U(Cot)(OTf)₂(py), which have been crystallographically characterised. The homoleptic species U(OTf)_n (n = 3, 4) are easily prepared by heating a mixture of uranium turnings or UH₃ in triflic acid. By adjusting the temperature to 120 or 180 °C, either U(OTf)₃ or U(OTf)₄ is isolated. Treatment of UO₃ with pure or aqueous solution of triflic acid leads to the non-solvated uranyl triflate UO₂(OTf)₂, which is more conveniently obtained by heating a suspension of UO₃ in triflic anhydride. This reactant is an excellent dehydrating agent and enables the preparation of UO₂(OTf)₂ and Ce(OTf)₄ from the hydrated starting materials.     

A planar chiral non-metallocenic analogue of the most popular N,N-dimethylbenzylaminate palladacycle

A racemic planar chiral tertiary amine pCp-CH₂NMe₂ (HL¹, pCp = [2.2]paracyclophane-4-yl) was prepared by aminomethylation of the bromide pCp-Br with Eschenmoser’s salt. Direct cyclopalladation of this new ligand with palladium(II) acetate results in the formation of the racemic CN-dimer rac-3 in a moderate yield of 64%. The enantiomerically pure dimer (S_pl, S_pl)-3 was obtained by the standard procedure of racemic palladacycle resolution using (S_C)-prolinate as a chiral derivatising agent. The ortho-palladated structure, absolute configuration of the chiral plane and stereochemical peculiarities of the new CN-palladacycle were established by means of NMR spectroscopy and an X-ray diffraction study of its (S_C)-prolinate derivative.     

New chiral scandium(III)/bisimine and diol complexes catalyzed asymmetric Diels-Alder reaction

Several bisimine and diol-based chiral ligands were examined as scandium(III) triflate complexes in the asymmetric Diels-Alder reaction of cyclopentadiene (2) with 3-acryloyloxazolidin-2-one (1) in the presence of 2,6-lutidine: the scandium/salen complex was revealed to be the most effective catalyst, which afforded the endo adduct in a good yield with 85% ee. Addition of a tertiary amine, such as 2,6-lutidine, was critical to achieve high enantioselectivity; enantioselectivity was remarkably decreased in the absence of the amine.     

An efficient enantioselective synthesis of (R,R)-formoterol,a potent bronchodilator,using lipases

The potent β₂-adrenergic receptor agonist formoterol (R,R)-1 has been obtained in enantiomerically pure form by a convenient chemoenzymatic approach by coupling of epoxide (R)-6 with the unprotected primary amine (R)-9. Both chiral precursors have been prepared by enantiodifferentiation processes involving Pseudomonas cepacia (lipase PS) and Candida antarctica lipase (CALB), respectively. For the resolution of amine 9, we have found that utilization of triethylamine as non-reactive base enhances the reaction rate and the enantioselectivity of the process. The key coupling reaction of (R)-6 and (R)-9 has been conducted through derivatization of the amine with the labile trimethylsilyl group, which liberates the amino group of the resulting amino alcohol (R,R)-11 upon column chromatography purification. In this way, the overall approach is shorter than others previously described.     

Convenient Route to Primary (Z)-Allyl Amines and Homologs

A convenient two-step procedure for the synthesis of primary (Z)-allyl amines, (Z)-homoallyl amines [(Z)-but-3-enylamines], and (Z)-pent-4-enylamines using the Wittig reaction was achieved. The use of nonstabilized ylides from triphenylphosphonium salt, potassium salt, and apolar solvent produced (Z/E)-geometric isomer ratios generally greater than 1.6. The amine moiety was masked using a phtalimide group that was removed successfully in the last step of the process in two different conditions, NH₂NH₂/EtOH/rt or CH₃NH₂/EtOH/rt. However, in some cases, reduction of the C = C double bond in the deprotection with hydrazine was concomitantly observed.     

Aqueous intermolecular diels-alder chemistry : Reaction of (e)-2,4-pentadienyl ammonium chloride and related ammonium salts with dienophiles in water

The aqueous Diels-Alder reactions of a series of dienyl ammonium chlorides derived from (E)-2,4-pentadienylamine, (E)-3,5-hexadienyl amine and (E)-4,6-heptadienyl amine with a variety of dienophiles have been examined. A similar Diels-Alder study employing the sodium salt of N-(E)-4,6-heptadienyl succinamic acid in water was also undertaken.     

Comparison of chiral NMR solvating agents for the enantiodifferentiation of amines

Chiral, enantiomerically pure organic-soluble acids are often used as NMR chiral solvating agents (CSAs) for analyzing the enantiopurity of amines. However, the reports that describe CSAs for amines provide limited comparisons to other previously reported reagents. As such, it is difficult to know which among the many CSAs to pick when studying a new amine. We report a comparison of thirteen commercially available CSAs for the analysis of primary, secondary and tertiary amines in chloroform-d. (R)-α-methoxyphenylacetic acid, (R)-(-)-O-acetylmandelic acid, (R)-2-methoxy-2-(1-naphthyl)propionic acid and (R)-(-)-1,1′-binaphthyl-2,2′-diylhydrogenphosphate are identified as the best four to use as a starting point for the analysis of a new amine.     

The asymmetric synthesis of cyclopentane derivatives by palladium-catalyzed coupling of prochiral alkylboron compounds

Treatment of the prochiral triflate 2a with Pd₂(dba)₃·CHCl₃, (S)-(R)-BPPFOAc and K₂CO₃, in THF at 40°C, gave the cyclopentane derivative 10 in 58% yield and in 28% ee after oxidative work-up and benzoylation. Moreover, reaction of the prochiral triflate 2c with Pd₂(dba)₃·CHCl₃, (S)-(R)-PPFA and K₂CO₃, in THF at 40°C, afforded the cyclopentane derivative 3b, with a quaternary carbon center, in 42% yield and in 31% ee after oxidative work-up.     

Vibrational spectra of N-2′-methyl-propyliden-propan-2-amine: conformational analysis and influence of the nitrogen hybridization

Infrared and Raman spectra of the (CH₃)₂C^2′HC^1′HNCH(CH₃)₂ aldimine (NPP) and of two deuterated derivatives at C^1′ and C^2′ in the liquid, solid and solution phases have been recorded and assigned between 4000 and 130 cm⁻¹. NPP adopts the E configuration and two conformers at the C_sp2 and N sides are in equilibrium. Some vibrational modes are specifically assigned to the anticlinal (ac) or synperiplanar (sp) conformers at the C_sp2 side. The ac(C_sp2) form is dominant in the pure liquid whilst the sp(C_sp2) form is favoured in the solid and in chloroform. The vibrational dynamics of the isopropyl group on both sides of the CN bond are partially similar to that of the (CH₃)₂CHCHO aldehyde on the one hand and of the (CH₃)₂CHNH₂ amine on the other hand. When moving from the amine to the corresponding aldimine, changes about νNC and wCC₂ modes (at the N side) are related to electronic and geometrical effects as a consequence of the nitrogen hybridization change from sp₃ to sp₂.     

GelatinnZn(CF3SO3)2 Polymer Electrolytes for Electrochromic Devices

The present work is focused on gelatin‐based electrolytes doped with a range of concentration of zinc triflate (Zn(CF₃SO₃)₂). The transparent‐thin‐film samples have been represented by the notation Gelatin_nZn(CF₃SO₃)₂, where n represents the zinc triflate salt concentration in the electrolyte membranes from 0.00 wt% to 10.93 wt% . The samples have been characterized by conductivity measurements, thermal analysis, cyclic voltammetry, X‐ray diffraction (XRD), polarized optical microscopy (POM) and scanning electron microscopy (SEM). The gelatin‐based electrolytes were also tested as ionic conductors in electrochromic devices with the glass/ITO/WO₃/gelatin‐based electrolyte/CeO₂‐TiO₂/ITO/glass configuration.     

Synthesis of enantiomerically pure (+)- and (−)-protected 5-aminomethyl-1,3-oxazolidin-2-one derivatives from allylamine and carbon dioxide

The stereoselective synthesis of enantiomerically pure (5R)- and (5S)-aminomethyl-oxazolidinones with different protecting groups have been carried out from an allyl amine as the source of the carbon backbone. The key reaction is the high yield iodiocyclization of enantiomerically pure allylphenethyl amine in the presence of carbon dioxide.     

Strong dual-state emission of unsymmetrical and symmetrical thiazolothiazole-bridged imidazolium salts

A novel thiazolothiazole-bridged imidazole derivative (1) was found to exhibit blue fluorescence in gaseous state or in methanol and yellow fluorescence in solid state. The N-alkylation of imidazole subunit(s) in 1 using n-propyl iodide generated unsymmetrically or symmetrically alkylated thiazolothiazole-bridged imidazolium salts with good water solubility and remarkably strong emission in solution. Furthermore, the replacement of iodide counter-anion by triflate or bis(trifluoromethane sulfonyl)imide achieved remarkably strong emission in solid state and in solution as well as good water solubility. The strong fluorescence of dicationic salts with triflate and NTf₂^– counter-anions in solid state can be ascribed to their twisted and rigid structures induced by interionic C?H···F hydrogen bonding.