Solvation lithium cations

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. 

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. ... 

Dr. Sternberg We believe that it is the solvated lithium cation that is being reduced at the cathode to solvated zero charged lithium atom. The solvated lithium then reacts with the coal. This latter reaction may be homogeneous or heterogeneous depending on whether the coal molecule is solvated or not. 

Very recently an X-ray structure of a -conjugated trimethylenemethane dianion derivative complexed to two TMEDA-solvated lithium cations has been described (40). In this n complex the most symmetrical form, with the lithium atoms lying along the threefold axis, is not lowest in energy instead, a less symmetrical structure was found. 

Recent studies have suggested that coordination with a lithium cation may be responsible for the stereochemical outcome in Meyers-type enolate alkylations . In fact, the hypothesis that the diastereofacial selectivity observed in these reactions might result from specific interactions with a solvated lithium cation was already proposed in 1990 . Nevertheless, the potential influence exerted by solvation and lithium cation coordination was not supported by a series of experimental results reported by Romo and Meyers , who stated that it would appear that neither the aggregation state of the enolate nor the coordination sphere about lithium plays a major role in the observed selectivity. This contention is further supported by recent theoretical studies of Ando , who carried out a detailed analysis of the potential influence of solvated lithium cation on the stereoselective alkylation of enolates of y-butyrolactones. The results showed conclusively that complexation with lithium cation had a negligible effect on the relative stability of the transition states leading to exo and endo addition. The stereochemical outcome in the alkylation of y -butyrolactones is determined by the different torsional strain in the endo and exo TSs. 

R = SiMes is formed in the above reactions as an intermediate in the presence of an excess of lithium metal, so this type of dimerization to 47 can be assumed here too (Schemes 10 and 11). Compound 47, of course, is not a l,4-dilithio-2-butene derivative but a delocalized dianion with two solvated lithium cations. 

Recent experiments revealed dependence between the rate of the racemization process and the concentration of the silyllithium compound 2 in solution. Due to decomposition the reaction rate cannot be determined exactly, but it is not simply first or second order. We believe that a solvated lithium cation plays an important role in the inversion process of 2. Thus, this process can be described by the interaction of the solvated lithium cation with compound 2 (model system 4). 

The solvated lithium cations should move within the media with high mobility. 

The examples discussed thus far are classed as contacted ion pairs, as both distinct metals are contained within the same molecule. Since 2007, one example of a solvent-separated lithium tris(aryl) magnesiate (ie, the complex exists as distinct cationic and anionic moieties) has been reported. [Li (THF)4] [Mg(mesityl)3] , 5 (where mesityl is 2,4,6-trimethylphenyl) resembles many other trialkyl/aryl Hthium magnesiates and consists of a tetrahedraUy disposed tetra-THF-solvated lithium cation and a trigonal planar magnesium tris(aryl) anion (Fig. 5). ... 

Compounds such as PhCH2Li and PhsCLi dissolve in ether forming solvated lithium cations and stable benzyl or benzyl-type anions (also solvated). Benzyl-lithium has been shown to be monomeric in tetrahydro-furan. The second condition, b), is met in the TMED complexes. 

Early work on polymer electrolytes indicated that polyethylene oxide (PEO) is a promising candidate as a host for lithium salt in relation to its ability to solvate Lithium cation [64-66]. This is attributed to its flexible ethylene oxide segments and ether oxygen atoms, which have a strong donor character and solvate lithium... 

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