Lithium Compounds Methyllithium

Anionic polymerization of vinyl monomers can be effected with a variety of organometaUic compounds alkyllithium compounds are the most useful class (1,33—35). A variety of simple alkyllithium compounds are available commercially. Most simple alkyllithium compounds are soluble in hydrocarbon solvents such as hexane and cyclohexane and they can be prepared by reaction of the corresponding alkyl chlorides with lithium metal. Methyllithium [917-54-4] and phenyllithium [591-51-5] are available in diethyl ether and cyclohexane—ether solutions, respectively, because they are not soluble in hydrocarbon solvents vinyllithium [917-57-7] and allyllithium [3052-45-7] are also insoluble in hydrocarbon solutions and can only be prepared in ether solutions (38,39). Hydrocarbon-soluble alkyllithium initiators are used directiy to initiate polymerization of styrene and diene monomers quantitatively one unique aspect of hthium-based initiators in hydrocarbon solution is that elastomeric polydienes with high 1,4-microstmcture are obtained (1,24,33—37). Certain alkyllithium compounds can be purified by recrystallization (ethyllithium), sublimation (ethyllithium, /-butyUithium [594-19-4] isopropyllithium [2417-93-8] or distillation (j -butyUithium) (40,41). Unfortunately, / -butyUithium is noncrystaUine and too high boiling to be purified by distiUation (38). Since methyllithium and phenyllithium are crystalline soUds which are insoluble in hydrocarbon solution, they can be precipitated into these solutions and then redissolved in appropriate polar solvents (42,43). OrganometaUic compounds of other alkaU metals are insoluble in hydrocarbon solution and possess negligible vapor pressures as expected for salt-like compounds. 

Another potentially useful amination procedure utilizes the reaction of organo-lithium compounds with mixtures of methoxyamine and methyllithium (Eqn. (85)) 343> for example ... 

The effect of a 3-substituent on the orientation of the addition of alkyl- and aryl-lithium compounds is interesting and salient results appear in Table 23. Attack at C-2 is favoured over that at C-6 unless either, or both, the C-3 substituent and the attacking alkyl group are very large. Reaction of isopropyllithium with 3-methylpyridine does not follow this trend. Benzyllithium is anomalous in that it attacks preferentially at C-4. A study of the relative rates of these alkylations revealed the remarkable fact that a 3-methyl or 3-ethyl group activates the 2-position (but not the 6-) towards attack by phenyllithium but not methyllithium. However, a 3-isopropyl and 3-cyclohexyl group deactivates C-2 relative to... 

Fig. 13. The reaction of 1,1-diphenylethylene with various lithium compounds in tetrahydrofuran. Variation of rate with formal concentration of lithium alkyl or aryl. (A) n-Butyllithium ( ) benzyllithium (- ) allyllithium (o) methyllithium ( ) vinyl-lithium (0) phenyllithium. Solvent tetrahydrofuran [101].

The isotopic fingerprint method has been applied to study the aggregation of alkyl and aryl lithium compounds [51,52,72,73], of lithium disopropylamide [72] and of mixed aggregates between methyllithium and Lil [51] as well as LiBr [53]. These studies revealed also the existence of isotope shifts transmitted over more than two bonds. In all cases high-frequency shifts for the Li resonance were observed. 

The products obtained from the reaction of (chloromethyl)trimethylsilane with organolithium reagents depend very much on the structure of the lithium compound. While lithium 2,2,6,6-tetramethylpiperidide initiates an a-elimination as described above, the treatment with sec-butyllithium leads to the formation of chloro(trimethylsilyl)methyllithium (11). This reagent cyclopropanates an electron-deficient alkene through sequential Michael addition and intramolecular ring closure (MIRC reaction), for example, the formation of cyclopropane 12. 

Halogen-free solutions may be obtained by cleavage of a disilane with elemental lithium or methyllithium, or by reaction of disilylmercury compounds with lithium. Other methods of preparation have been reviewed1, and this same source discusses the Grignard-like reactions of silyllithium and other silylmetal reagents. 

This compound, as might have been expected, also has a high melting point, 372°-380 C (with dec.) as contrasted with the linear isomer, octadeca-methyloctasilane, which melts at 61°-62°C. Lithium and methyllithium react with the hexakis compound to cause cleavage of the symmetrical... 

A nice example, which is still a matter of debate, is the nature of bonding in the simplest organometalhc compound, methyllithium. In the solid state it forms tetramers [Li4(CH3)4] (Figure 10.43), which are further linked into a three-dimensional network. Related aggregates are found for other alkyl lithium compounds. The distances within these tetramers are Li-Li 2.588 A and Li-C 2.256 A. Both values are well below the sum of radii of the pairs used in automated routines to draw bonds between close lying atoms ( bond(C) = 0.77, rbond(Li) = 1 -52 A, plus an allowance of 0.25 A added for each atom). Such automated... 

At low temperatures perfluoro-w-propyllithium, prepared in the above manner, underwent displacement and addition reactions common to alkyl-lithium compounds. The experimental technique (7) involved addii methyllithium and the reactant dissolved in ether to heptafluoro- -propyl iodide in the same solvent. In this manner, certain aldehydes and ketones afforded the expected alcohols, and diethyldichlorosilane gave a mixture of the organosilanes n-C3F7(C2H5)2SiCl and ( -C3F7)2Si(C2H5)2. 

Although ethereal solutions of methyl lithium may be prepared by the reaction of lithium wire with either methyl iodide or methyl bromide in ether solution, the molar equivalent of lithium iodide or lithium bromide formed in these reactions remains in solution and forms, in part, a complex with the methyllithium. Certain of the ethereal solutions of methyl 1ithium currently marketed by several suppliers including Alfa Products, Morton/Thiokol, Inc., Aldrich Chemical Company, and Lithium Corporation of America, Inc., have been prepared from methyl bromide and contain a full molar equivalent of lithium bromide. In several applications such as the use of methyllithium to prepare lithium dimethyl cuprate or the use of methyllithium in 1,2-dimethyoxyethane to prepare lithium enolates from enol acetates or triraethyl silyl enol ethers, the presence of this lithium salt interferes with the titration and use of methyllithium. There is also evidence which indicates that the stereochemistry observed during addition of methyllithium to carbonyl compounds may be influenced significantly by the presence of a lithium salt in the reaction solution. For these reasons it is often desirable to have ethereal solutions... 

Seven procedures descnbe preparation of important synthesis intermediates A two-step procedure gives 2-(HYDROXYMETHYL)ALLYLTRIMETH-YLSILANE, a versatile bifunctional reagent As the acetate, it can be converted to a tnmethylenemethane-palladium complex (in situ) which undergoes [3 -(- 2] annulation reactions with electron-deficient alkenes A preparation of halide-free METHYLLITHIUM is included because the presence of lithium halide in the reagent sometimes complicates the analysis and use of methyllithium Commercial samples invariably contain a full molar equivalent of bromide or iodide AZLLENE IS a fundamental compound in organic chemistry, the preparation... 

Problem 1.8 concerned the charge distribution in methane (CH4), chloromethane (CH3CI), and methyllithium (CH3Li). Inspect molecular models of each of these compounds, and compare them with respect to how charge is distributed among the various atoms (carbon, hydrogen, chlorine, and lithium). Compare their electrostatic potential maps. 

A similar stereospecific conjugate addition to epoxysulfone 323 was also observed416. When this reaction of 323 was carried out with methyllithium at — 78 °C dichloromethane-diethyl ether (1 1) in the presence of lithium perchlorate, compounds 324 and 325 were obtained in a ratio of 95 5. On the other hand, in the treatment of 323... 

The combination of equimolar amounts of tris(trimethylsilyl)methyllithium and zinc bromide in a THF/diethyl ether mixture, Scheme 27, furnished tris(trimethylsilyl)methylzinc bromide, as a lithium bromide/ether adduct.43 The compound, which may also be formulated as a lithium alkyldibromozincate, showed no ligand redistribution reactions. It is monomeric in solution and can be treated with 1 equiv. of an organolithium reagent to afford heteroleptic diorganozinc compounds. 

The submitters used an ether solution of halide-free methyl-lithium, purchased from Foote Mineral Company, and the checkers prepared the compound from methyl chloride and lithium metal in ether according to the literature.2 The solution was standardized before use by the titration procedure described in a previous volume of this series.3 The checkers observed that use of a halide-containing ether solution of methyllithium resulted in a considerable decrease in yield of the product, principally due to difficulty in following the subsequent procedure described in the text. 

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