Mechanistic study of asymmetric Michael addition of malonates to enones catalyzed by a primary amino acid lithium salt

A mechanistic study was carried out for the asymmetric Michael addition reaction of malonates to enones catalyzed by a primary amino acid lithium salt to elucidate the origin of the asymmetric induction. A primary β-amino acid salt catalyst, O-TBDPS β-homoserine lithium salt, exhibited much higher enantioselectivity than that achieved with the corresponding catalysts derived from α- and γ-amino acids for this reaction. Detailed studies of the transition states with DFT calculations revealed that the lithium cation and carboxylate group of the β-amino acid salt catalyst have important roles in achieving high enantioselectivity in the Michael addition reaction of malonates to enones.     

Mixed aggregates of dilithiodiamines with alkyllithiums and lithium enolates

The formation of mixed aggregates of N,N′-dilithiodiamines with alkyllithiums and lithium enolates was investigated. Enolization of 3-pentanone with the dilithium salt of N,N′-dimethyl-1,3-propanediamine generated both the E and Z enolates and the E/Z ratio changed in the presence of a lithium enolate or excess butyllithium. The formation of mixed aggregates was modeled with the B3LYP DFT method and it was found that mixed aggregate formation is energetically favorable. The infrared spectra of dilithio-N,N′-dimethyl-1,3-propanediamine in the presence of excess butyllithium or lithium enolate are consistent with the formation of mixed aggregates.     

Thermal and ionic‐conductive behaviors of liquid crystalline polymers with alkali metal salt

In order to investigate the relationship between ionic conductivity and liquid crystallinity, we prepared the main‐chain type polyester having 1,4‐bisstyrylbenzene units and ethyleneoxide chain in the repeating unit. The main‐chain type polyester with lithium salt at the ratio of 0.04 per polymer repeating unit exhibited a smectic phase. However, the polyester with lithium salt (0.11) showed a nematic phase. The ionic conductivity of the polyester with lithium salt increased with increasing lithium salt concentration. The trans‐type polyester exhibited a liquid crystalline phase, while the cis‐type polyester did not show any mesophase. We found that the ionic conductivity of the trans‐type polyester with lithium salt (0.11) was larger than that of the cis‐type polyester with lithium salt (0.11). However, a liquid crystalline phase was found in the side‐chain type polyether with alkoxy chain length of below 12. A smectic phase was induced for the non‐mesomorphic polyethers with lithium salt. The layer spacing of the smectic A phase for the non‐mesomorphic polyether with lithium salt decreased from 55 to 41 Å with increasing temperature. The ionic conductivity of the polyether with lithium salt increased with decreasing the layer spacing. Copyright © 2001 John Wiley & Sons, Ltd.     

Diastereoselective lithium salt-assisted 1,3-dipolar cycloaddition of azomethine ylides to the fullerene C60

An efficient method for the diastereoselective synthesis of 5-substituted 3,4-fulleroproline esters based on the lithium salt-assisted cycloaddition of azomethine ylides has been developed. A series of the fulleroproline esters containing either electron donating or electron withdrawing substituents was prepared with high yields and diastereoselectivities provided by the S-trans-configuration of ylide generated in situ from the corresponding Schiff base in the presence of a lithium salt and base. This method provides easy preparation of 3,4-fulleroproline derivatives suitable for fullerene-based peptide synthesis.     

Urea and thiourea complexes with trifluoromethanesulfonic acid and its derivatives

Urea and thiourea form complexes with trifluoromethanesulfonic acid, its monohydrate, and lithium salt CF₃SO₃Li. Urea complexes with trifluoromethanesulfonic acid are also formed as a result of hydrolysis in the reaction of N,N′-bis(trimethylsilyl)carbodiimide or cyanamide with trifluoromethanesulfonic acid in water.     

Ternary diffusion coefficients of diethylene glycol and lithium chloride in aqueous solutions containing diethylene glycol and lithium chloride

In this work, ternary diffusion coefficients of diethylene glycol and lithium chloride in aqueous solutions containing diethylene glycol and lithium chloride were reported for temperatures (303.2, 308.2, and 313.2 K) using the Taylor dispersion method. The investigated ternaries contained total glycol–salt concentrations of 10, 15, and 20 wt%. The main diffusion coefficients (D₁₁ and D₂₂) and the cross-diffusion coefficients (D₁₂ and D₂₁) were discussed as function of temperature and concentration. A modified equation originally proposed by Batchelor [1] for mixture of hard spheres in a continuum solvent was used to correlate the present diffusion coefficient data and the results are satisfactory.     

One-pot synthesis of a novel C1-symmetric diphosphine from 1,3-cyclic sulfate. Asymmetric hydroformylation of styrene

Preparation of a novel homochiral diphosphine with C₁-symmetry from the cyclic sulfate of (2R,4R)-2,4-pentanediol is reported. Reaction of a lithium phosphide salt with the cyclic sulfate affords a γ-phospholylsulfate which can be converted to a diphosphine ligand on treatment with a second equivalent of lithium phosphide. Using this ligand in the platinum-catalyzed asymmetric hydroformylation of styrene, outstanding levels of regio- and enantiocontrol were obtained (89/11 iso/n isomeric ratio and 89% e.e.). The results are compared with those obtained with the analogous ligands (bdpp and bdbpp) having C₂-symmetry. The novel unsymmetric ligand possessed the advantageous catalytic features of the C₂-symmetric parent ligands.     

New synthesis of t-butyl arylpropiolates using diazo(trimethylsilyl)methylmagnesium bromide

Diazo(trimethylsilyl)methylmagnesium bromide smoothly reacted with t-butyl aryl(oxo)acetates to afford the corresponding arylpropiolates via alkylidenecarbene intermediates. In this reaction system, the magnesium bromide salt of trimethylsilyldiazomethane was significantly efficient compared to the lithium one, commonly known as a reagent for the conversion of aldehydes and aryl ketones into acetylenes.     

The first example of an enantiopure planar chiral hydroxyferrocene ligand

Lithiation of 2-ferrocenyl-4,4-dimethyloxazoline followed by addition of bis(trimethylsilyl)peroxide led to the isolation of air-stable 2-(2-hydroxyferrocenyl)-4,4-dimethyloxazoline. Repetition of this procedure on (S)-2-ferrocenyl-4-(1-methylethyl)oxazoline gave the lithium salt of (S)-2-((_pS)-2-hydroxyferrocenyl)-4-(1-methylethyl)oxazoline, a stable precursor to the first example of an enantiopure hydroxyferrocene ligand.     

Synthesis of enantiomeric pure lithium and potassium benzamidinate complexes

A new synthesis leading to the chiral amidines (S,S)- and (R,R)-N,N-bis-(1-phenylethyl)benzamidine ((S)- and (R)-HPEBA) in good yields is presented. Further reaction of (S)-HPEBA with n-BuLi gave the chiral lithium salt (S)-LiPEBA. Treatment of KH with (S)-HPEBA in boiling THF afforded the corresponding potassium salt (S)-KPEBA. In contrast by performing the reaction in boiling toluene a fast racemization was observed. In the solid state racemic KPEBA formed a dimer, in which all four nitrogen atoms are in a plane. To each potassium atom a toluene molecule is η⁶-coordinated.     

Li+-templated complexation of cylindrical macrotricyclic host with naphthalene diimide: Cation-controlled switchable complexation processes

Anthracene-based cylindrical macrotricyclic polyether (1) containing two dibenzo-30-crown-10 cavities has been proved to be an efficient host for the templated complexation with N,N’-dipropyl-1,4,5,8-naphthalenetetracarboxylic diimide in the presence of lithium ions in both solution and solid state. Host 1 could also form 1:1 complex with the bispyridinium salt with two β-hydroxyethyl groups in solution and in the solid state. Moreover, it was also found that the switchable complexation processes between the macrotricyclic host and two different kinds of guests could be chemically controlled by the addition and removal of lithium ions.     

Dipheno-silyliminoquinones - A 14π-system

Lithium salts of 2.6-dialkylanilines react with di-tert-butylfluorosilanes to give mono (1-3) - and bis (7, 8)-(2.6-dialkylphenylamino)silanes. Amino-2.6-dimethylphenyl-(di-tert-butylfluoro)silane (1) forms with BuLi a dimeric lithium salt (4) containing an eight-membered (LiFNSi)₂ ring system. Thermally, 4 loses LiF and a bicyclic compound (9) via iminosilenes is obtained. The lithium salt of the bulkier amino-2.6-diisopropylphenyl-(di-tert-butylfluorosilanes) (5-7) thermally loses LiH and iminosilanes (10-12) with a 14π-system are isolated. The reaction mechanisms and crystal structures are discussed.     

Stereoselective preparation of O-alkoxy d-tetrose,d-pentose, 2-deoxy-d-glycero tetrose and 2,3-dideoxy-d-erythro pentose derivatives by an iterative elongation of 2,3-O-isopropylidene-d-glyceraldehyde

All d-pentoses are synthesized by one-carbon chain elongation commencing with the addition of the lithium salt of ethyl ethylthiomethyl sulfoxide to 2-O-(t-butyldimethylsilyl)-3,4-O-isopropylidene-d-erythrose and d-threose, 16 and 17. The addition of the above-mentioned nucleophile to 2-deoxy-3,4-O-isopropylidene-d-glycero tetrose, 19, gave rise to 2,3-dideoxy-d-glycero pentose. The starting aldehydes, 16, 17 and 19, are easily available from 2,3-O-isopropylidene-d-glyceraldehyde, 1, and ethyl ethylthiomethyl sulfoxide.     

A novel “inorganic salt-polymer salt” hybrid system as a solid state electrolyte

Poly{2-methacryloyl-3-[ω-methoxyoligo(oxyethylene)]propanesulfonate lithium} (PMMOEPLi), a new kind of polymer salt intended for “inorganic salt-polymer salt” hybrid systems, was synthesized. This polymer salt has high flexibility and high polarity. Upon addition of PMMOEPLi to LiClO₃ based electrolytes, ionic conductivities as high as 10⁻³ S/cm were obtained at ambient temperature. In the electrolyte studied Li⁺ dominates the conductivity, making this material a good candidate for application in lithium rechargeable batteries.     

Preparation and characterization of blended solid polymer electrolyte 49% poly(methyl methacrylate)-grafted natural rubber:poly(methyl methacrylate)–lithium tetrafluoroborate

The preparation and characterization of blended solid polymer electrolyte 49% poly(methyl methacrylate)-grafted natural rubber (MG49):poly(methyl methacrylate) (PMMA) (30:70) were carried out. The effect of lithium tetrafluoroborate (LiBF₄) concentration on the chemical interaction, structure, morphology, and room temperature conductivity of the electrolyte were investigated. The electrolyte samples with various weight percentages (wt.%) of LiBF₄ salt were prepared by solution casting technique and characterized by Fourier transform infrared spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy. Infrared analysis demonstrated that the interaction between lithium ions and oxygen atoms occurred at symmetrical stretching of carbonyl (C=O) (1,735 cm^?1) and asymmetric deformation of (O–CH₃) (1,456 cm^?1) via the formation of coordinate bond on MMA structure in MG49 and PMMA. The reduction of MMA peaks intensity at the diffraction angle, 2θ of 29.5° and 39.5° was due to the increase in weight percent of LiBF₄. The complexation occurred between the salt and polymer host had been confirmed by the XRD analysis. The semi-crystalline phase of polymer host was found to reduce with the increase in salt content and confirmed by XRD analysis. Morphological studies by SEM showed that MG49 blended with PMMA was compatible. The addition of salt into the blend has changed the topological order of the polymer host from dark surface to brighter surface. The SEM analyses supported the enhancement of conductivity with the addition of salt. The conductivity increased drastically from 2.0 to 3.4?×?10^?5 S cm^?1 with the addition of 25 wt.% of salt. The increase in the conductivity was due to the increasing of the number of charge carriers in the electrolyte. The conductivity obeys Arrhenius equation in higher temperature region from 333 to 373 K with the pre-exponential factor σ _o of 1.21?×?10^?7 S cm^?1 and the activation energy E _a of 0.46 eV. The conductivity is not Arrhenian in lower temperature region from 303 to 323 K.     

Dual-Phase structure of polymer electrolytes comprised of NBR/SBR latex films swollen with lithium salt solution

Dual-phase polymer electrolytes (DPE) that have high ionic conductivity (> 10^?3 S/cm) and good mechanical strength were prepared by mixing NBR and SBR latices and casting films. The latex films absorbed large quantities of lithium salt solution (e.g., 1M lithium perchlorate in γ-butyrolactone) to obtain DPE films but did not dissolve with swelling. The NBR phase is polar and was impregnated selectively with the polar lithium salt solution, whereas the SBR phase is nonpolar and formed a mechanically-supportive matrix. Transmission electron microscopic (TEM), electron energy loss spectral (EELS), and energy-dispersive x-ray (EDX) analyses showed microscopically the dual-phase structure. Evidence for swelling by lithium salt solution was found only in the NBR phase and not in the SBR phase by EDX microanalysis. Ionic conductivity as a function of NBR content or swelling degree showed clearly that a percolation threshold for ionic conductivity exists. © 1994 John Wiley & Sons, Inc.     

Poly(ethylene oxide)-polyurethane/poly(acrylonitrile) semi-interpenetrating polymer networks for solid polymer electrolytes: vibrational spectroscopic studies in support of electrical behavior

Studies on solid polymer electrolyte systems based on semi-interpenetrating polymer networks of poly(ethylene oxide)-polyurethane and poly(acrylonitrile) (PEO-PU/PAN) doped with lithium trifluoromethanesulfonate (LiCF₃SO₃) is reported. Room temperature FT-IR analysis indicates a salt solvation process that occurs predominantly in the polyether segments of the semi-IPNs and incorporation of salt is also seen to favor a morphological change in the matrix with a transition from semi-crystalline to amorphous phase. From the relative band areas a critical concentration (C_c) of salt can be identified where concentration of ionic species, morphology and amount of transient crosslinks is optimal to impart maximum conductivity, which is in agreement with the room temperature conductivity results. Thermal analysis of the semi-IPN lends further support to this observation. The temperature dependence of conductivity is found to follow the Arrhenius behavior at low temperatures (∼ upto 328 K) and VTF dependence at higher temperatures. This crossover in temperature dependent conductivity is attributed to the change in the phase morphology of the semi-IPNs beyond the crystalline melting temperature (T_m1) of the polyether segments.     

Thermochemical and Electrochemical Stability of Electrolyte Systems based on Sulfolane

UV spectroscopy and cyclic voltammetry were used to examine the thermochemical and electrochemical stabilities of liquid sulfolane-based electrolyte systems for lithium and lithium-ion batteries. It was found that solutions of lithium salts in sulfolane are stable in prolonged keeping at 100°C. The thermochemical stability of lithium salt solutions in sulfolane changes in the order LiBF₄ > LiClO₄ ≈ LiN(CF₃SO₂)₂ > LiCF₃SO₃. It was shown that the electrochemical stability of lithium salt solutions in sulfolane is in the range from 5.5 to 5.9 V (relative to Li/Li⁺) and prolonged action of high temperatures (100°C) does not yield electrochemically active thermal destruction products.     

Cationic and anionic environments in LiTFSI-doped di-ureasils with application in solid-state electrochromic devices

Fourier Transform mid-infrared and Raman spectroscopies were used to investigate the cation/polymer, cation/urea bridge, cation/anion and hydrogen bonding interactions in poly(oxyethylene) (POE)/siloxane di-ureasil networks prepared by the sol–gel route and doped with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Materials with compositions 200 ?n ? 5 (where n expresses the molar ratio OCH₂CH₂/Li⁺) were studied. The Li⁺ ions coordinate to the urea carbonyl oxygen atoms over the whole range of salt concentration considered. Bonding to the ether oxygen atoms of the POE chains occurs at n ? 40, although a significant fraction of the POE chains remain non-coordinated. In these high salt content samples, the cations interact with the anions forming contact ion pairs. “Free” ions are probably the main charge carriers at the room temperature conductivity maximum of these ormolytes.     

Electrochemical performances of two kinds of ternary electrolyte mixtures with lithium bis(oxalate)borate

Conductivities (??) of PC (propylene carbonate)/EMC (ethyl methyl carbon ate)/DMC (dimethyl carbonate) and EC (ethylene carbonate)/EMC/DMC solutions of lithium bis(oxalate)borate (LiBOB) were experimentally determined at a temperature (??) range from ?40.0 to 60.0°C. Under such experimental conditions, the effect factors on the ??, such as the salt molar concentrations (m), and the volume ratio of solvent compositions, were also investigated. The results showed that, in wide ?? range, the higher ?? were obtained with 0.7 mol L^?1 LiBOB in PC/EMC/DMC and 0.6 mol L^?1 LiBOB in EC/EMC/DMC and with a volume ratio of 1: 1: 1 and 1: 1: 2, respectively. When used in LiFePO₄/Li cells, compared to the cell with the electrolyte system of 1.0 mol L^?1 LiPF₆-EC/EMC/DMC (1: 1: 1), LiBOB cells with PC/EMC/DMC and EC/EMC/DMC electrolyte systems with the same volume mixture solvent compositions exhibit several advantages, such as more stable cycle performance, higher mean voltage, excellent large current discharge capability, more capacity retention at high temperature, and more stable storage performance, etc. This study not only shows that LiBOB is a very promising alternative salt for lithium ion chemistry, but also provides appropriate solvent to improve LiBOB??s electrochemical performance.