Cations lithium cation solvation

Using dilatometry in parallel with cyclic voltammetry (CV) measurements in lmolL 1 LiC104 EC-l,2-dimethoxy-ethane (DME), Besenhard et al. [87] found that over the voltage range of about 0.8-0.3 V (vs. Li/Li+), the HOPG crystal expands by up to 150 percent. Some of this expansion seems to be reversible, as up to 50 percent contraction due to partial deintercalation of solvated lithium cations was observed on the return step of the CV. It was concluded [87] that film formation occurs via chemical reduction of a solvated graphite intercalation compound (GIC) and that the permselective film (SEI) in fact penetrates into the bulk of the HOPG. It is important to repeat the tests conducted by Besenhard et al. [87] in other EC-based electrolytes in order to determine the severity of this phenomenon. 

The smaller ion may intercalate faster into the graphite galleries. Reaction (5) may be the rate-determining step for the solvent co-intercalation process, and if so, molecules that form large and stable solvated lithium cations will have a smaller tendency for co-intercalation into the graphite. 

A similar reasoning may explain the difference in reactivities of the lithium and sodium ion-pairs in THF. The larger ionic radius of the sodium than that of the lithium cation, favoring the formation of loose pairs, makes the sodium pair much more reactive than the lithium salt at lower temperatures. However, at higher temperatures the sodium salt becomes less reactive than the lithium salt as it looses its solvation more readily than the latter. 

Sulfur diimides react quantitatively with organolithium reagents at the sulfur centre to produce lithium sulfinimidinates of the type Li[RS(NR )2] A. The lithium derivatives may be hydrolysed by water to R NS(R)NHR which, upon treatment with MH (M=Na, K) or the metal (M=Rb, Cs) in THF, produces the heavier alkali-metal derivatives.132 The structures of these complexes are influenced by (a) the size and electronic properties of the R group, (b) the size of the alkali metal cation, and (c) solvation of the alkali-metal cation. 

An ideal electrolyte solute for ambient rechargeable lithium batteries should meet the following minimal requirements (1) It should be able to completely dissolve and dissociate in the nonaqueous media, and the solvated ions (especially lithium cation) should be able to move in the media with high mobility. (2) The anion should be stable against oxidative decomposition at the cathode. (3) The anion should be inert to electrolyte solvents. (4) Both the anion and the cation should remain inert toward the other cell components such as separator, electrode substrate. 

Aside from cyclic carbonates, the decomposition products from linear carbonates were also identified in the forms of either lithium alkyl carbonates or alkoxides, as shown by Scheme 7 and also in Table 6a. 1 5,271,279 Relatively, the reduction of linear carbonates was thought to be less consequential as compared to their cyclic counterparts, apparently due to their smaller presence in the solvation sheath of lithium cations. i H 1 1... 

One additional example involves alkylation of the lithium salt of the anthracene anion-radical by 2-octyl fluoride (Herbert et al. 1985). The akylation does not occur in DME (which strongly solvates Li+), whereas it is facilitated and leads to the quantitative yield in diethyl ether. Diethyl ether is much less active at solvation of the lithium cation. That makes >CH-F Li+ coordination possible and assists the formation of octylanthracene. 

The effect of solvation in CH2=CHOLi was studied in detail. Earlier studies at the B3LYP/6-31+G level suggested that the lowest energy minima correspond to isolated bridged lithium enolate 2a, rather than the open-chain strnctnre 2b this is attributed to the interaction of the lithium cation with the enolate anion (Fignre 3). 

Because of the highly solvated sodium cation, the latter sodium lithiate is thermally instable (Figure 33). The Li—N distances are not different from the related distances in the previous section. Firstly synthesized, however, were the lithium lithiates by employment of the bulky tris(trimethylsilyl)methyl (MesSiisC anion. Two of them coordinate linearly a single lithium cation (Figure 33). 

The TMEDA and THE complexes of the very sterically crowded methyllithium derivative tris(trimethylsilyl)methyUithium (9, Scheme 1) were studied by multinuclear solid state NMR spectroscopy in combination with solution NMR spectroscopy and X-ray crystallography to reveal the strucmre and dynamic behaviour of the complexes . In the solid state, this complex crystallizes as an ate-complex, with one lithium cation interacting with two substituted methyl anions while the other lithium cation is complexed by two TMEDA ligands. In solution, the afe-complex is partly transformed into solvated monomers or aggregates, depending on the experimental conditions. 

From these investigations it is clear that the Li chemical shift gives a clear indication of the lithium cation position when there are direct effects from ring currents in delocalized anions. However, as shown for the quinuclidine CIP and THF SSIP fluorenyllithium complexes, the correct assignment cannot be reached solely based on the chemical shifts. Furthermore, there is no clear-cut information about solvation to be gained from the chemical shifts. As we discuss in the following Section, the quadrupolar interaction is much more sensitive to these effects. In order to obtain maximal structural information from Li NMR spectroscopy, the chemical shift should be determined and used in combination with the quadrupolar coupling constant. 

Without solvation, fluorenyllithium has been shown to crystallize as a dimeric sandwich structure where the lithium cations interact with the fluorenyl units in rf" fashions. ... 

In many cases the temperature dependence of the quadrupolar coupling constant is an indicator of dynamic processes, because the symmetry around the lithium cation is affected by motions which are fast on the NMR time scale. If the rate of these processes exceeds 1/x, the effective symmetry around the lithium cation increases and a decrease in x( Li) results. In Li MAS spectra, a broadening of the satellite transitions can be observed which eventually disappear completely if the rate of the dynamic process comes in the order of the quadrupole frequency. This behaviour was observed for the THF solvated dimer of bis(trimethylsilylamido)lithium, where the Li MAS spectrum at 353 K shows only the central transition and the sidebands caused by CSA and homonuclear Li- Li dipole coupling (Figure 27) . The simulation of the high-temperature spectrum yielded —20 ppm and 1300 Hz for these quantities, respectively. The dipole coupling agrees closely with the theoretical value of 1319 Hz calculated from the Li-Li distance of 2.4 A, which was determined by an X-ray study. 

The study of the interactions between organic compounds and aUtali-metal cations, in the gas phase, is related to many topics such as ion solvation, catalysis and molecular recognition. Furthermore, mass spectrometry has been used for the analyses of organolithium compounds and supramolecular assemblies that contain lithium cations. Alkali cationization is an important ionization technique, implemented for the analyses of a wide range of organic compounds. Finally, gas-phase studies are also useful for the quantitative determination of lithium cation affinity. The interaction between lithium cation and organic substances is thus related to different aspects of gas-phase chemistry and mass spectrometry. 

An extensive review appeared on the configurational stability of enantiomeric organolithium reagents and the transfer of the steric information in their reactions. From the point of view of the present chapter an important factor that can be evaluated is the ease by which an inversion of configuration takes place at the metallation site. It happens that H, Li, C and P NMR spectra of diastereotopic species have been central to our understanding of the epimerization mechanism depicted in equation 26, where C and epi-C represent the solvated complex of one chiral species and its epimer, respectively. It has been postulated that inversion of configuration at the Li attachment site takes place when a solvent-separated ion pair is formed. This leads to planarization of the carbanion, its rotation and recombination to form the C—Li bond, as shown in equation 27, where Li+-L is the solvated lithium cation. An alternative route for epimerization is a series of... 

Organolithium compounds of structure 275 can been applied as transfer agents for transition metal ions, for example, as shown in equation 54 for scandium(III) with tetrahedral coordination (276). The structure of these complexes, elucidated by XRD crystallography, shows the transition metals forming part of an anionic entity, paired to solvated lithium cations. Further structural information can be obtained from H, and "B NMR spectroscopies. ... 

With this model, it is necessary to assume fast inversion of the two corannulene units within the dimer (or planarity) otherwise the top and bottom bowls would not be equivalent in the NMR spectra. MNDO calculations predict an activation enthalpy of approximately 13 kcal/mol for the concerted inversion process, and this value is inconsistent with the NMR behavior that shows no evidence of freezing out such a dynamic process. These calculations, however, do not take solvation of the exterior lithiums into account, and so the exterior lithiums were removed, and the system was calculated under conditions that would roughly model solvent separation of the lithium cations. Accordingly, the approximate barrier for inversion was lowered to approximately 1 kcal/mol, suggesting that solvation of the exterior lithium cations can indeed greatly reduce the inversion barrier. ... 

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