Download presentation
Presentation is loading. Please wait.
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 are not 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 positions well-determined used for enantioselective deprotonation 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 of intramolecular 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
Similar presentations
© 2024 SlidePlayer.com. Inc.
All rights reserved.