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OrganoLithium Compounds

OrganoLithium Compounds. Peter H.M. Budzelaar. Organo-lithium compounds. Ionic character, electron-deficient oligomeric or polymeric structures Strongly basic and nucleophilic applications in organic synthesis Reducing unwanted side reactions. Organo Na, K compounds. "Purely" ionic

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OrganoLithium Compounds

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  1. OrganoLithium Compounds Peter H.M. Budzelaar

  2. Organo-lithium compounds • Ionic character, electron-deficient • oligomeric or polymeric structures • Strongly basic and nucleophilic • applications in organic synthesis • Reducing • unwanted side reactions OrganoLithium Compounds

  3. Organo Na, K compounds • "Purely" ionic • polymeric structures • pyrophoric solids • mostly insoluble in any solvent they don't react with • Very strong bases, not that good as nucleophiles • few applications • organoLi compounds are much easier to handle OrganoLithium Compounds

  4. Driving force for oligomerization • ionic interpretation: Ionic interactions are "soft"but not weak! OrganoLithium Compounds

  5. Driving force for oligomerization • covalent interpretation 2e-3c and 2e-4c bonds arenot just bonding between Li and C,but also bonding between the Li atoms OrganoLithium Compounds

  6. Structure of [EtLi]4 OrganoLithium Compounds

  7. Structure of [CyLi]6 OrganoLithium Compounds

  8. Structure of [BuLi(THF)]4 OrganoLithium Compounds

  9. Structure of [o-Me2NCH2C6H4Li]4 OrganoLithium Compounds

  10. Structure of [2,6-(MeO)2C6H3Li]4 OrganoLithium Compounds

  11. Structure of [MeLi(sparteine)]2 not all hydrogen positionswell-determined used forenantioselectivedeprotonation OrganoLithium Compounds

  12. Structure of PhLi(pmdta) OrganoLithium Compounds

  13. Structure of (Allyl)Li(pmdta) 2.33 2.25 2.72 OrganoLithium Compounds

  14. Structure of [BzNa(pmdta)]∞ OrganoLithium Compounds

  15. Structure of [(Me3Si)3CRb]∞ OrganoLithium Compounds

  16. Structure of (naphthalene)[Li(tmeda)]2 OrganoLithium Compounds

  17. Synthesis of OrganoLi Compounds Direct synthesis • Reactivity: alkyl > aryl, Cl < Br < I etc • Commercial synthesis: mostly from chlorides • In laboratory: usually from alkyl bromides/iodides (easier to start) • Complication: Li reacts with N2, do reaction under Ar ! • Side reaction: Wurtz coupling, especially for X = I • In apolar or weakly polar solvents • Radical mechanism Transmetallation • M less electropositive than Li • Infrequently used OrganoLithium Compounds

  18. Reactions of OrganoLi Compounds Metallation • Faster for more basic R- • Faster in polar and/or coordinating solvents • Works well if product capable ofintramolecular coordination Metal-halogen exchange • 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 (-80 to -20°C) OrganoLithium Compounds

  19. Reactions of OrganoLi Compounds Metathesis • Driving force: stability of LiCl (lattice energy!) • Selective synthesis of RlMXm often hard • With excess RLi often "ate" complexes (Rn+1M-) OrganoLithium Compounds

  20. Structure of [(tmeda)LiMe2]2Mg OrganoLithium Compounds

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