Transcript Organolithium Compounds

Organolithium Compounds
• Ionic character
• Electron-deficient
oligomeric or
polymeric structures
• Strongly basic
• Strongly nucleophilic
applications in
organic synthesis
• Reducing
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Organolithium Compounds
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Organo Na, K, ... compounds
• "Purely" ionic
polymeric structures,
mostly insoluble
• Very strong bases
few applications
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Organolithium Compounds
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Oligomeric Li compounds:
ionic interpretation
+ -
+ +
-
+ + +
+
-
Ionic interactions are "soft"
but not weak!
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Oligomeric Li compounds:
covalent interpretation
Li
Li
Li
C
2e-3c and 2e-4c bonds
also bonding between the Li atoms
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Organolithium Compounds
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[Me3SiCH2Li]6
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Organolithium Compounds
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[MeLi·(THF)]4
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Organolithium Compounds
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[n-BuLi·(tmeda)]2
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Organolithium Compounds
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PhLi
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Organolithium Compounds
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PhLi·(pmdta)
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[PhNa(pmdta)]2
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(allyl)Li·(pmdta)
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Organolithium Compounds
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[2,6-(MeO)2C6H3Li]3
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Organolithium Compounds
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(napthalene)[Li(tmeda)]2
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Synthesis of
Organolithium Compounds
Direct synthesis
RX + Li
–
–
–
–
RLi + LiX
Reactivity: alkyl > aryl, Cl < Br < I, Li < Na etc
Side reaction: Wurtz coupling, especially for X = I
In apolar of weakly polar solvents
Radical mechanism
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Synthesis of
Organolithium Compounds
Transmetallation
RM + Li
RLi + M
– M less electropositive than Li
– Infrequently used
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Reactions of
Organolithium Compounds
Metallation
RLi + R'H
R'Li + RH
– Faster for more basic R– Faster in polar and/or coordinating solvents
– Works well if product capable of
intramolecular coordination
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Reactions of
Organolithium Compounds
Metal-halogen exchange
RLi + R'Br
–
–
–
–
R'Li + RBr
Facile for I and Br, usually (too) slow for Cl, F
Regioselective synthesis of R'Li
Side reaction: Wurtz coupling
Usually done at low temperature
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Reactions of
Organolithium Compounds
Metathesis
n RLi + MXn
n LiCl + RnM
– Driving force: stability of LiCl (lattice energy!)
– Selective synthesis of RlMXm often hard
– With excess RLi often "ate" complexes (Rn+1M-)
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Organolithium Compounds
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[(tmeda)LiMe2]Mg
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