Methyllithium oligomers

Table 9 Lithium Charges (electrons) in Methyllithium Oligomers as Obtained by Three Methods of Electron Density Analysis ...

However, a detailed reexamination within the framework of Kohn-Sham MO theory leads us to a view that differs in a number of ways.51 In the following, we show that the C—Li bond in CH3Li (25) may very well be envisaged as an electron pair bond (24b), although a rather polar one, of course. But our point is not just the shift of the bonding picture back to the more covalent side of the 24a-24b spectrum. In particular, if we go to the oligomers (e.g., the methyllithium tetramer 27), a fundamentally new phenomenon occurs in the C—Li bonding mechanism. This phenomenon emphasizes the presence of dis-... 

Structurally similar tetramers are maintained in solutions with electronic donors (THF or TMEDA). For example, the same core structure exists for the methyllithium TMEDA adduct. Ab initio methods have been used to study the aggregation of various methyl lithium oligomers in the presence of various donor ligands. The heavier alkali metal (M = K, Rb, Cs) methyl compounds have more ionic... 

Methyllithium attacked the sulfur atom of naphthothiete 205 to give 231 and oligomers 232 and 233 via 8-mercaptomethyl-l-lithionaphthalene. Treatment with lithium aluminum hydride followed by methylation gave 234. Treatment of thiete 215 with triphenylphosphine leads to ring-expanded products possibly via nucleophilic attack by phosphorus on sulfur. ... 

Many organolithium compounds are soluble in hydrocarbons exceptions are methyllithium and phenyllithium w hich are associated in these solvents. Butyllithium is mostly hexameric and /c/Y-butyllithium is tetrameric in cyclohexane. A Lewis basic solvent can interact with an organolithium oligomer, thereby decreasing the degree of association. Thus, methyllithium. which is tetrameric in the solid phase, becomes a solvated tetramer in ether, and BuLi. hexameric in hydrocarbons, becomes tetrameric in ether. In the more basic THE BuLi has a degree of association between dimeric and tetrameric at -108 °C, and phenyllithium is between monomeric and dimeric [3]. 

The mixed complexes formed between methyllithium and lithium bromide or iodide, in diethyl ether between 180 and 220 K, were studied using Li NMR with the bromide, there is coexistence of tetramers Li (CH3), Li (CH3)3Br, Li (CH3)2Br2, and of oligomers (LiBr)j. With the iodide system, only Li (CH3), Li (CH3)3l, and (Lil)j are present (102). 

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