1. 6/3/2015Organomagnesium Compounds1 Organo Be and Mg Compounds Ionic character Electron-deficient Basic Nucleophile Reducing oligomeric or polymeric structures Mg: applications in organic synthesis (Grignard) Be: extremely toxic

2. 6/3/2015Organomagnesium Compounds2 Organo Ca, Sr,... Compounds Very ionic Strongly basic polymeric structures, usually insoluble few applications

3. 6/3/2015Organomagnesium Compounds3 Grignards RMgX Direct synthesis ("Grignard reaction"): Mechanism is not simple! Almost certainly involves SET (Single Electron Transfer). Very sensitive to traces of impurities (Na, K, transition metals) in the Mg, and to the nature of the Mg surface.

4. 6/3/2015Organomagnesium Compounds4 Direct Synthesis Reactivity: I > Br > Cl >> F Selectivity: I gives largest amounts of side products In ethers In Et 2 O cleaner than in THF, but also slower Also in ether/hydrocarbon mixtures Side reactions: –Wurtz coupling –Radical rearrangements

5. 6/3/2015Organomagnesium Compounds5 Main application of Grignards: Addition to C=X Sometimes radical mechanism (especially for aromatic ketones) :

6. 6/3/2015Organomagnesium Compounds6 Complication in C=X addition: Reduction For Grignards having a  -hydrogen:

7. 6/3/2015Organomagnesium Compounds7 Grignards RMgX "Barbier reaction": Selectivity differs from that of Grignard addition. Probably radical mechanism.

8. 6/3/2015Organomagnesium Compounds8 RMgX en R 2 Mg "Schlenk" equilibrium: (is really more complicated) Shifts through addition of ligands:

9. 6/3/2015Organomagnesium Compounds9 MeMgBr(THF) 3

10. 6/3/2015Organomagnesium Compounds10 Me 2 Mg(pmdta)

11. 6/3/2015Organomagnesium Compounds11 (diiminate)MgMe

12. 6/3/2015Organomagnesium Compounds12 Me 2 Mg 4 Cl 6 (THF) 6