Asymmetric Reduction Using Lithium Aluminum Hydride Modified with Chiral Ligands Prepared from (1R)-(-)-β-Pinene

The reduction of prochiral ketones using chiral reducing reagents, prepared from lithium aluminum hydride and (-)-(1R, 2S, 3S, 5R)-10-anilinopinanediol (5) and (-)-(1R, 2S, 3S, 5R)-10-N-methylanilinopinanediol (6), affords chiral secondary alcohols in useful chemical yields (70 ～ 93%) but in low optical purity (8 ～ 33% ee). Modifiers 5 and 6 are synthesized from (lR)-(-)-β-pinene in three steps.     

Methyl methacrylate polymerization at samarium(II)-grafted MCM-41

Sm(II)-modified periodic mesoporous silica (PMS), Sm[N(SiHMe₂)₂]₂(THF)_x@MCM-41, was used for the synthesis of Sm(II) alkyl, alkoxide, and indenyl surface species via secondary ligand exchange. The performance of the novel Sm(II)-based organometallic–inorganic hybrid materials as initiators for the graft polymerization of methyl methacrylate (MMA) is reported. All of the Sm(II) hybrid materials including the new PMMA–PMS composites were characterized via N₂ physisorption, elemental analysis, FTIR spectroscopy, and scanning electron microscopy (SEM). The organic–inorganic composites revealed complete pore blockage as well as enrichment and strong adhesion of the polymer at the exterior of the porous silica material.     

Effect of the ZnNi y Mn2– y O4 (0 ≤ y ≤ 1) spinel composition on electrochemical lithium insertion

The electrochemical insertion of lithium in the spinel-type manganite with the formula ZnNi _y Mn_{2– y} O₄ has been studied. The galvanostatic discharge curves show that the best performance is obtained for y = 0.25, where a tetragonal to cubic structural transformation occurs. The thermodynamics and kinetics of the process of insertion of the lithium into the tetragonal spinel Li _x ZnNi_0.25Mn_1.75O₄ (x = 0.05–1.3) have been studied. The molar thermodynamic quantities, such as enthalpy, entropy and free energy determined by EMF-T measurements, varied with the lithium concentration in the oxide structure, and a major variation was observed around x = 0.8. The chemical diffusion coefficient of lithium in these spinels was also determined. Structural analysis, degree of oxidation and magnetic susceptibility measurements were carried out for the lithiated oxides in order to obtain the cationic distribution as a function of x. It has been possible to demonstrate that, upon lithium insertion, Mn⁴⁺ ions on B sites are reduced to Mn³⁺ and then to Mn²⁺. A cooperative Jahn-Teller effect is present in these spinel manganese-nickel oxides. Received: 4 February 1997 / Accepted: 11 April 1997     

Base-freie Tris(trimethylsilyl)methyl-Derivate des Lithiums,Aluminiums, Galliums und Indiums

Base-free Tris(trimethylsilyl)methyl Derivatives of Lithium, Aluminium, Gallium, and Indium Base-free LiR* (R*=-C(SiMe₃)₃) has been prepared from R*Cl and Li-metal in toluene at 85?90°C and used to synthesize the metallanes R*MMe₂ with M = Al, Ga and In, respectively. The NMR (¹H, ¹³C, ²⁹Si) and the vibrational spectra of these trisyl compounds have been discussed. AlCl₃ and LiR*(ratio 1 : 1) forms the metallate metallate Li[R*AlCl₃]. The triclinic unit cell (space group P1 ) consists of a centrosymmetric assoziate, formed by four Li[R*AlCl₃]- units with Al? Cl…?Li bridges, two pairs of Li-atoms differing in their chlorine-coordination and two disordered toluene molecules, inserted in the crystal lattice (R₁wR₂ =0,0444/0,1072). The reaction of GaCl₃ with LiR* (I :1) gives the unusual sesquichloride (R*Ga(Cl_1,33)Me_0,67)₃ in moderate yield. The X-ray structure determination shows a Ga₃Cl₃-skeleton with chairconformation and disordered, terminal gallium ligands (R₁/wR₂= 0,0646/0,2270).     

Optimization of alkali-alkalkine earth cation separation on weak cation-exchangers

Summary The elution behavior of alkali and earth alkaline cations has been studied on a newly synthesized weak cationexchanger (WCX). Applying this stationary phase isocratic separation of these cations is possible. The dependence of retention on competing ion concentration is described via a simple model. The influence of crown ethers as well as organic eluent additives on selectivity and peak efficiency is demonstrated. With optimized separation such cations can be determined with detection limits of about 0.5 ppm using a conductivity detector without ion suppression.     

Thermal dehydration of lithium metaborate dihydrate and phase transitions of anhydrous product

Reaction steps and mechanisms of the thermal dehydration of lithium metaborate dihydrate were investigated by means of thermoanalytical measurements, high temperature powder X-ray diffractometry, FT-IR spectroscopy, and microscopic observations. The first half of thermal dehydration was characterized by the melting of the sample producing viscous surface layer, the formation of bubbles on the particle surfaces, and the sudden mass-loss taking place by an opportunity of cracking and/or bursting of the bubble surface layer. The second half of the dehydration with a long-tailed mass-loss process in a wide temperature region was divided further into three distinguished reaction steps by the measurements of controlled rate thermal analysis. During the course of the thermal dehydration, four different poorly crystalline phases of intermediate hydrates were observed, in addition to an amorphous phase produced by an isothermal annealing. Just after completing the thermal dehydration, an exothermic DTA peak of the crystallization of β-LiBO₂ was appeared at around 750 K. The phase transition from β-LiBO₂ to α-LiBO₂ was observed in the temperature range of 800-900 K, which subsequently melted by indicating a sharp endothermic DTA peak with the onset temperature at 1101.4 ± 0.6 K.     

Syntheses of 2-arylated 1-benzazocines via Beckmann rearrangement

One-step and highly efficient syntheses of 2-aryl-1-benzazocines via Beckmann rearrangement of 5H-benzocyclohepten-5-one oxime mesylates in dry toluene was described, in which aryl Grignard reagents were used for the first time to induce Beckmann rearrangement directly without any additional protic agents. Iodotrimethylsilane was also employed to promote Beckmann rearrangement of the mesylates, followed by the treatment of the intermediate imidoyl iodide with phenylmagnesium bromide to complete the synthesis of benzazocines.     

Intercalation materials for lithium rechargeable batteries

An overview is given of intercalation materials for both the negative and the positive electrodes of lithium batteries, including the results of our own research. As well as lithium metal as a negative electrode, we consider insertion materials based on aluminium alloys. In the case of the positive electrode metal-oxides based on manganese, nickel and cobalt are discussed. Received: 27 May 1997 / Accepted: 30 July 1997     

Selective lithium ion extraction with chromogenic monoaza crown ethers

Two chromogenic monoaza crown ethers were synthesized and investigated for their lithium extraction capabilities. The chromogenic monoaza 14-crown-4 compound exhibited the best selectivity for lithium over sodium; ca. 2800, with a detection limit of 0.08 ppm.