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Syntheses of Organolithium Compounds:有机锂化合物的合成
Organolithium Compounds
Umbreen Mir
CHM 331S
Prof. M. Denk
April 12th, 2000
History
Over the years, organolithium compounds have gained an increasing value in chemical synthesis due to their high reactivity, relatively easy preparation and solubility in inert solvents.4
The first attempt to synthesize an organolithium compound was with the reaction of lithium with diethyl mercury.10 Methyl-lithium was first prepared by Schlenk and Holtz in 1917.16 In 1930, the first successful synthesis of alkyllithiums was obtained from lithium metal and alkyl halides.10
This fundamental method is still widely employed for the “direct” synthesis of organolithium compounds. However, this method has not been well understood in the past. New insights have unfolded over the years on the by-products, such as hydrocarbons (from coupling), alkanes, and alkenes, corresponding to the alkyl halides, which suggest that radicals may be involved.10
Figure 1: Mechanism of possible stereochemical pathways.10
Metal-halogen exchange and transmetallation, as well as new procedures have been introduced to avoid producing racemic species.10
Structures of simple organolithium compounds
Efforts have been made in characterizing the structure of important reagents, both in solution and in the solid state. Several different forms of these reagents have been determined, because the degree of association is strongly dependent on the nature of the solvent used.3
Table 1: Aggregation of Typical Organolithium Compounds 3,7
Compound Method Used Solvent Aggregation Methyl-lithium
X-ray crystallography THF, Et2O
Hydrocarbons
TMEDA Tetrameric
Hexameric
Monomeric n-butyl-lithium
IR and NMR Hydrocarbons
Ether Hexameric
Tetrameric s-butyl-lithium
To date, no crystal structures have been determined13 t-butyl-lithium
Mass spectroscopy Hydrocarbons Predominantly tetrameric, but some hexameric particles present Phenyl-lithium
X-ray powder diffraction THF, Et2O Dimeric
In 1964, Weiss and Lucken deduce
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