Chapter 14; Organometallic Compounds

1. Chapter 14;Organometallic Compounds Definition Nomenclature Synthesis Acid/Base Reaction

2. Li Cyclopropyllithium CH3CH2MgCH2CH3 CH3MgI Diethylmagnesium Methylmagnesiumiodide Organometallic Compound Nomenclature; 1) Metal is Parent A. OrganoLithium Cpds; B. Grignard Reagents; R-MgX

3. – + R M Carbon-Metal Bond in Organometallic Compoundsmakes Carbon Nucleophilic F 4.0 H 2.1 O 3.5 Cu 1.9 N 3.0 Zn 1.6 C 2.5 Al 1.5 H 2.1 Mg 1.2 Li 1.0 Na 0.9 K 0.8

4. R X + 2Li R Li + LiX Synthesis of Organolithium Compounds normally prepared by reaction of alkyl halides with lithium Examples diethylether (CH3)3CCl + 2Li (CH3)3CLi + LiCl –10°C (75%)

5. + Li+ •– • [R X] R X + Li Li• • • + R• R Li X– • • Electron Bookkeeping Step 1; Li gives up valence electron to form + ion; R-X receives electron and becomes unstable radical anion Step 2; Unstable radical anion dissociates Step 3; Two free radical form organometallic compound

6. R X + Mg diethylether Br + Mg MgBr 35°C (95%) Synthesis of Grignard Reagents prepared by reaction of alkyl halides with magnesium RMgX Examples

7. + Mg+ •– • [R X] R X + Mg • Mg+ • • • + R• R Mg+ X– X– • • • Electron Bookkeeping Step 1; Mg gives up valence electron to form + ion; R-X receives electron and becomes unstable radical anion • • • Step 2; Unstable radical anion dissociates Step 3; Two free radical form organometallic compound

8. Carbon-Metal Bond is so Polarized that it is almost ionic In Organometallic Compounds; Carbon is a Carbanion • Carbon is Basic • Acid/Base Rxns Organometallic Compounds will react with anything with an acidic H; OH, SH, or NHx group

9. Table 14.2Approximate Acidities Compound pKa (CH3)3CH 71 CH3CH3 62 CH4 60 Ethylene 45 Benzene 43 Ammonia 36 Acetylene 26 Water 16 Hydrocarbons are very weak acids. Their conjugate bases are very strong bases. Grignard reagents and organolithium reagents are strong bases.

10. + H2O CH3CH2CH2CH2Li LiOH CH3CH2CH2CH3 + + CH3OH MgBr Acid-Base Reactions + CH3OMgBr