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Concept
Organolithium reagent
Summary
In organometallic chemistry, organolithium reagents are chemical compounds that contain carbon–lithium (C–Li) bonds. These reagents are important in organic synthesis, and are frequently used to transfer the organic group or the lithium atom to the substrates in synthetic steps, through nucleophilic addition or simple deprotonation. Organolithium reagents are used in industry as an initiator for anionic polymerization, which leads to the production of various elastomers. They have also been applied in asymmetric synthesis in the pharmaceutical industry. Due to the large difference in electronegativity between the carbon atom and the lithium atom, the C−Li bond is highly ionic. Owing to the polar nature of the C−Li bond, organolithium reagents are good nucleophiles and strong bases. For laboratory organic synthesis, many organolithium reagents are commercially available in solution form. These reagents are highly reactive, and are sometimes pyrophoric.
Studies of organolithium reagents began in the 1930s and were pioneered by Karl Ziegler, Georg Wittig, and Henry Gilman. In comparison with Grignard (magnesium) reagents, organolithium reagents can often perform the same reactions with increased rates and higher yields, such as in the case of metalation.
Since then, organolithium reagents have overtaken Grignard reagents in common usage.
Although simple alkyllithium species are often represented as monomer RLi, they exist as aggregates (oligomers) or polymers.
The degree of aggregation depends on the organic substituent and the presence of other ligands. These structures have been elucidated by a variety of methods, notably 6Li, 7Li, and 13C NMR spectroscopy and X-ray diffraction analysis. Computational chemistry supports these assignments.
The relative electronegativities of carbon and lithium suggest that the C−Li bond will be highly polar.
However, certain organolithium compounds possess properties such as solubility in nonpolar solvents that complicate the issue.
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