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Chapter 14 Organometallic Compounds

Chapter 14 Organometallic Compounds. 14.1 Organometallic Nomenclature. Li. H 2 C. CH Na. Cyclopropyl lithium. Vinyl sodium. CH 3 CH 2 Mg CH 2 CH 3. CH 3 Mg I. Diethyl magnesium. Methyl magnesium iodide. Metal is the parent. 14.2 Carbon-Metal Bonds in Organometallic Compounds.

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Chapter 14 Organometallic Compounds

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  1. Chapter 14Organometallic Compounds

  2. 14.1Organometallic Nomenclature

  3. Li H2C CHNa Cyclopropyllithium Vinylsodium CH3CH2MgCH2CH3 CH3MgI Diethylmagnesium Methylmagnesiumiodide Metal is the parent

  4. 14.2Carbon-Metal BondsinOrganometallic Compounds

  5. Table 14.1 (p 547) 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

  6. R X R X Polarity of Bonds organometallics are a source of nucleophilic carbon d+ d– d– d+

  7. Polarity of Bonds CH3F CH3Li

  8. 14.3Preparation of Organolithium Compounds

  9. R X + 2Li R Li + LiX Organolithium Compounds normally prepared by reaction of alkyl halides with lithium is an oxidation-reduction reaction: carbon is reduced same for Ar—X

  10. Examples diethylether (CH3)3CCl + 2Li (CH3)3CLi + LiCl –10°C (75%) diethylether Br + 2Li Li + LiBr 35°C (95-99%)

  11. [R X] R X + Li • • R Li X– • • Electron Bookkeeping + Li+ •– • Li• + R•

  12. 14.4Preparation of Organomagnesium Compounds: Grignard Reagents

  13. R X + Mg Grignard Reagents prepared by reaction of alkyl halides with magnesium Diethyl ether is most often used solvent. Tetrahydrofuran is also used. RMgX same for Ar—X

  14. Cl MgCl Examples diethylether + Mg –10°C (96%) diethylether Br + Mg MgBr 35°C (95%)

  15. [R X] R X + Mg • Mg+ • • • R Mg+ X– X– • • • Electron Bookkeeping • • + Mg+ •– • + R•

  16. Order of Reactivity I > Br > Cl >> F RX > ArX

  17. Forbidden Groups certain groups cannot be present in the solvent the halide from which the Grignard reagent is prepared the substance with which the Grignard reagent reacts

  18. Forbidden Groups Anything with an OH, SH, or NH group therefore cannot use H2O, CH3OH, CH3CH2OH, etc. as solvents cannot prepare Grignard reagent from substances such as HOCH2CH2Br, etc.

  19. 14.5Organolithium and Organomagnesium Compounds as Brønsted Bases

  20. R H R H – •• + M M OR' OR' •• •• Brønsted basicity Grignard reagents (M = MgX) and organolithium reagents (M = Li) are strong bases. d+ d– •• ••

  21. Example water is a stronger acid than butane + H2O CH3CH2CH2CH2Li CH3CH2CH2CH3 + LiOH (100%)

  22. Example methanol is a stronger acid than benzene + CH3OH MgBr + CH3OMgBr (100%)

  23. Table 14.2Approximate Acidities of Hydrocarbons Hydrocarbon 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.

  24. HC CH HC CMgBr Acetylenic Grignard Reagents are prepared by an acid-base reaction + CH3CH2MgBr stronger acid + CH3CH3 weaker acid

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