Preparation of lithium stannide mixtures in organic solvents. A alternate source of lithium in organolithium chemistry

Lithium stannides were prepared from lithium naphthalenide and tin (II) chloride or tin (0) powder in THF solvent at room temperature under dry argon atmosphere. They were characterized with elemental analysis, XRD, and solid ^6,7Li NMR. Stabilities and reactivities of lithium stannides prepared from different conditions were tested and showed they were stable for a limited time at low temperatures. Best reactivity was obtained when they were prepared from tin (II) chloride and an excess of lithium naphthalenide. The lithium stannide mixture can reductively cleave carbon-halogen bonds and yield pinacol coupling with aldehydes. Organolithium compounds prepared from lithium stannides and organic halides add to ketones or aldehydes under Barbier conditions.     

Hetero-aggregate compounds of aryl and alkyl lithium reagents: a structurally intriguing aspect of organolithium chemistry

Organolithium compounds are often depicted as mononuclear species. However, such compounds are in fact aggregated species and can form hetero-aggregates containing different organic groups, including heteroatom groups. In reactions involving organolithium reagents, the "pure" homo-aggregate organolithium compound can change into a hetero-aggregate, which has a different structure and reactivity to the homo-aggregate. This fact is often overlooked. When there are chiral centers in the organolithium reagent or the substrate, diastereoselective self-assembly (the preferential formation of a particular diastereoisomeric aggregate) plays a role. The importance of these contributions in understanding the structure and reactivity patterns of organolithium reagents is the focus of this Minireview.     

Aldo Domenicano and the structural chemistry of substituent effects: a personal tribute

Aldo Domenicano has been a provider and interpreter of structural information on substituent effects, especially in benzene derivatives. He started in X-ray crystallography, continued in gas-phase electron diffraction, and eventually added quantum chemical computations to his arsenal of tools of research. He was a charter member of the Editorial Board of Structural Chemistry; he has served the community in other ways as well, such as with directing international schools and editing monographs. He has also been an esteemed colleague and faithful friend.     

A theoretical study of substituent effects on allylic ion and ion pair SN2 reactions

An ab initio study of ionic and ion pair displacement reactions involving allylic systems has been carried out at the RHF/6-31+G* level. The geometries and natural charges show the absence of conjugative stabilization in the ionic transition states, thus differing from traditional explanations. The high reactivity of allyl halides is explained by electrostatic polarization of the double bond. Substituent effects were also studied; in general, electron-withdrawing groups lower the barriers of the ionic S(N)2 reactions but increase the barriers of the ion pair reactions. The allylic reactions are compared with related benzylic systems. Hammett correlations give rho of opposite sign for the ionic and ion pair displacement reactions, in agreement with some experimental results.     

Relativistic effects in gas-phase ion chemistry: an experimentalist's view

Gas-phase experiments provide information which, in conjunction with results from electronic structure calculations, help to unravel the critical role relativistic effects play in many areas of transition-metal chemistry. Examples include the thermochemical data of gold halides in different oxidation states, the fascinating structural properties of gold(I) complexes, the dramatic effects of ligands on the ionization energy of gold, or the binding in cationic metal-carbene complexes. Furthermore, in the context of methane functionalization, special emphasis is paid to the chemistry of cationic metal-carbene complexes, and at uncovering the mechanistic details of important carbon-heteroatom coupling reactions. It is the interplay of conducting experiments of "isolated" molecules under well-defined conditions with reliable electronic structure calculations that has considerably improved our understanding of the role relativistic effects play in the context of transition-metal chemistry, catalysis, and beyond.     

Sequestering agent for uranyl chelation: new binaphtyl ligands

The synthesis of phosphonate, sulfocatecholamide (CAMS) and hydroxypyridinone (HOPO) binaphtyl ligands is presented. Their binding abilities for uranyl cation were determined by UV spectrophotometry in aqueous media versus pH. These titrations showed that the efficiency of these chelating agents depends on the nature of the chelating group. Each ligand shows a more or less pronounced affinity towards uranium. While the bisphosphonate compound did not show any affinity towards the uranyl ion, the BINHOPO derivative exhibits significant affinity at acidic and neutral pH while the BINCAMS is more efficient at basic pH.     

Sequestering agents for uranyl chelation: new calixarene ligands

Synthesis of sulfocatecholamide (CAMS) and hydroxypyridinone (HOPO) calixarene ligands and determination of their binding abilities for the uranyl cation were described. Chelating properties were determined by UV spectrophotometry in aqueous media under various pH conditions and further studied by ¹H NMR analysis of the resonance signals of both aromatics' protons of the chelating groups. Each ligand shows a more or less pronounced affinity for uranium. HOPO calixarenes exhibit significant affinity towards uranyl ion at acidic and neutral pH while CAMS calixarene is more efficient at basic pH.     

Complex formation of certain neutral sulfur ligands with the lithium ion in tetrahydrofuran

Complex formation of a new group of ligands with the lithium ion has been studied in THF. Stability constants of the [LiL]⁺ complexes have been determined. It was found that the R-S group does not take part in the coordination; the complex-forming capability of the R-S=O group with the lithium ion is no higher than that of Ph₂P=O or (EtO)₂P=O.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2216–2218, October, 1989.     

Covalent modification of natural graphite with lithium benzoate multilayers via diazonium chemistry and their application in lithium ion batteries

In this study, we present an alternative pathway for the surface modification of anode materials of lithium ion batteries via molecular design. Aromatic multilayers of lithium benzoate were covalently attached to the surface of natural graphite through diazonium chemistry, and the resulting graphite exhibited superior electrochemical performance as anode material of lithium ion batteries. The mechanism responsible for the improved electrochemical behavior was ascribed to the formation of a stable and compact passive film that can accommodate the volume change of graphite particles. Due to the diversity and reliability of diazonium chemistry, this study may provide a new strategy to modify the conventional anode or even cathode materials of lithium ion batteries.     

Hypericin derivatives: substituent effects on radical-anion formation

The electron-transfer properties of the hypericin derivatives, dibromo-, hexaacetyl-, hexamethyl- and desmethylhypericin, were studied. Cyclovoltammetric measurements revealed that dibromo- and desmethylhypericin have almost the same redox potentials as the parent hypericin. Substitution of the hydroxyl groups by acetoxy leads to less negative E1/2 values, whereas methoxy substitution induces more negative values. Electron paramagnetic resonance (EPR)/electron nuclear double resonance/general TRIPLE spectroscopy and quantum mechanical calculations were used to establish the structure of the one-electron reduced stages of hypericin derivatives. Proton loss in the bay region, already demonstrated for hypericin, was also found for dibromo- and desmethylhypericin. The spin and charge of the radical ions are predominately confined to the central biphenoquinone moiety of the hypericin skeleton. Generation of the radical ions by in situ electrolysis indicates that the redox potentials of hypericin, dibromo- and desmethylhypericin, containing hydroxyls at the 1, 3, 4, 6, 8 and 13 positions, largely depend on the solvent. With phosphate-buffered saline (pH 7.4)/dimethylsulfoxide (DMSO) as the solvent the EPR spectra of the corresponding radical ions appear at markedly lower potentials than in pure DMSO and N,N'-dimethylformamide. However, this effect is not observable for hexaacetyl- and hexamethyl-hypericin-lacking hydroxyl groups. In all cases the EPR data and calculations revealed the presence of 7,14 tautomers.     

Non-trivial temperature effects on the cation exchange chromatography and chelation ion chromatography of metal ions

The effect of column temperature upon the retention of metal ions on sulfonated and mono-, di-, and amino-carboxylated cation exchange columns has been investigated. The retention of alkali, alkaline earth and transition metal ions on each of the above types of cation exchanger was studied over the temperature range 19-65 degrees C. A major difference between the behaviour of mono- and divalent metal ions was shown on each of the above stationary phases, with the monovalent alkali metals exhibiting clearly exothermic behaviour (a decrease in retention with increased temperature) under acidic eluent conditions and an apparent relationship between retention factor and the magnitude of the temperature effect. The effect of temperature upon alkaline earth metal ions was less defined, although strongly endothermic behaviour (increase in retention with temperature) could be seen on all stationary phases through correct choice of eluent. The transition metal ions studied showed endothermic behaviour on all four stationary phases, with the sulfonated column unexpectedly showing the largest increases in retention. The above behaviour can be partially explained through the dominance of the type of solute-stationary phase interaction governing retention. In several of the above columns, both ion-exchange and surface complexation interactions can occur, with the effects of temperature indicating which process dominates under specific eluent conditions.     

Nonlocal ion potential effects on the optical response of lithium clusters

We present a spherical symmetry model, containing explicitly nonlocal effects in the electron-ion interaction, to describe the electronic properties of lithium clusters. We assume either an optimized discrete ionic structure or a jellium structure. The model provides the nonlocal potential from which the random phase approximation with exact exchange is applied to calculate the optical response of Li clusters. The optical response of Li ₁₃₉ ⁺ obtained within this model is in good agreement with the measured giant dipole resonance. The same model is used to predict alkali-metal effective masses; the agreement with band structure calculations is emphasized.     

Nicotine chemistry : The addition of organolithium reagents to (—)-nicotine

Organolithium reagents (RLi; where R = ethyl, isopropyl,cyclopropyl,n-butyl, sec-butyl, t-butyl, vinyl) have been found to add regiospecifically to (—)-nicotine to provide a series of 6-substituted nicotinoids of low optical activity. The data presented for the organolithium additions coupled with an analysis of the addition oft-BuLi to(—)-nicotine and [2'-²H]nicotine have provided strong evidence for a novel racemization process caused by pyrrolidine ring-opening and reclosure involving nicotine's N'—C'₂ bond.     

Crystal chemistry and electronic structure of the metallic lithium ion conductor, LiNiN

The layered ternary nitride LiNiN shows an interesting combination of fast Li+ ion diffusion and metallic behavior, properties which suggest potential applications as an electrode material in lithium ion batteries. A detailed investigation of the structure and properties of LiNiN using powder neutron diffraction, ab initio calculations, SQUID magnetometry, and solid-state NMR is described. Variable-temperature neutron diffraction demonstrates that LiNiN forms a variant of the parent Li3N structure in which Li+ ion vacancies are ordered within the [LiN] planes and with Ni exclusively occupying interlayer positions (at 280 K: hexagonal space group Pm2, a = 3.74304(5) A, c = 3.52542(6) A, Z = 1). Calculations suggest that LiNiN is a one-dimensional metal, as a result of the mixed pi- and sigma-bonding interactions between Ni and N along the c-axis. Solid-state 7Li NMR spectra are consistent with both fast Li+ motion and metallic behavior.     

New synthesis of zinc tetrakis(arylethynyl)porphyrins and substituent effects on their redox chemistry

Sonogashira coupling of zinc 5,10,15,20-tetraethynylporphyrin with various phenyl iodides under mild conditions afforded good yields of the corresponding zinc porphyrins. This method is applicable to a variety of aryl iodides including meso-substituted iodoporphyrin to form a conjugated star-shaped multiporphyrin. The UV-Vis spectra show that peak broadening, red shifts, and changes in the oscillator strength of absorptions increase with the extension of pi-conjugation. In the electrochemical measurements, the first oxidation of porphyrins 4-9 occurs at potentials in the range +0.89 to +1.08 V, which are comparable to that of ZnTPP (TPP = tetraphenylporphyrin). The first reduction was observed at potentials from -0.73 to -0.89 V, which is anodically shifted by 390-550 mV as compared to that of ZnTPP, and the second reduction occurs at potentials in the range -1.12 to -1.33 V. The para-substituted tetrakis(phenylethynyl)porphyrins show substituent effects on their redox chemistry and exhibit only slight substituent effects in their emission and absorption maxima.     

Study on effects of carboxymethyl cellulose lithium (CMC-Li) synthesis and electrospinning on high-rate lithium ion batteries

This study, for the first time, synthesized carboxymethyl cellulose lithium (CMC-Li) by a two-step method and applied it to modified electrode material by electrospinning and as a binder on a lithium ion battery. By electrospinning, nano CMC-Li fiber and CMC-Li/9, 10-anthraquinone (AQ) composite fiber were obtained successfully and coated AQ electrode material. AQ was uniformly distributed in fibers, and then CMC-Li/AQ composite fiber was carbonized to obtain the carbon nanofiber/AQ/Li [CAL] composite as lithium battery anode material. Also for the first time we investigated substituting aqueous CMC-Li with different degrees of substitution (DS) for oily polyvinylidene fluoride (PVDF) as a lithium battery binder to assemble the battery with CAL for electrochemical performance tests. Compared with PVDF binder, cells with CMC-Li for a binder have excellent advantages, such as higher discharge capacity (226.4 mAh g^?1), safer cycle performance, lower cost and being more eco-friendly. Furthermore, the cell with CMC-Li with high DS performed better than the cell with low DS. This method also applies to other electrode materials.     

Attenuation of substituent effects on reactivities of low-spin iron(II) complexes of Schiff base ligands

Substituent effects on reactivity are compared for base hydrolysis of tris-ligand-iron(II) complexes of Schiff base ligands derived from 2–acetylpyridine and substituted benzylamines and their aniline analogues. The methylene spacer in the former effectively isolates the iron from substituent effects in the phenyl ring, as indicated by the almost equal rate constants for base hydrolysis of the complexes derived from benzylamine and its 4–methyl, 4–fluoro, and 4– trifluoromethyl derivatives. Rate constants for base hydrolysis of the (substituted) benzylamine derivatives are also reported for some Me2CO-H2O and DMSO-H2O solvent mixtures. Reaction is faster in all these binary aqueous mixtures, mainly due to the higher chemical potentials of hydroxide ion.     

Sequestering agent for uranyl chelation: a new family of CAMS ligands

The synthesis of new dipodal bis-sulfocatecholamide uranophiles is presented. Their binding abilities for uranyl cation were determined by UV spectrophotometry in aqueous media under various pH conditions and further studied by ¹H NMR analysis of the resonance signal of both aromatic protons of the sulfocatecholamide groups. The results showed that the efficiency of these hydrosoluble chelating agents depends on the nature of the spacers. Each ligand shows a more or less pronounced affinity for uranium. The best receptor is the ligand CYCAMS 5d obtained as a mixture of cis/trans isomers, which achieves the best compromise between rigidity and steric hindrance.     

The catalyzed hydrosilation reaction: substituent effects

Ab initio electronic structure calculations using MP2 wavefunctions have been used to investigate a reaction path for the hydrosilation reaction catalyzed by divalent titanium [modeled by TiH₂, TiCl₂, and Ti(C₅H₅)₂]. Optimized structures and energies are presented. All model reactions predict a barrierless reaction path compared to a barrier of 78 kcal/mol for the uncatalyzed reaction. Received: 11 August 1998 / Accepted: 3 September 1998 / Published online: 23 February 1999