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Chapter 14 Organometallic Compounds

Chapter 14 Organometallic Compounds. Dr. Wolf's CHM 201 & 202. 14-1. 14.1 Organometallic Nomenclature. Dr. Wolf's CHM 201 & 202. 14-2. 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.

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Chapter 14 Organometallic Compounds

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  1. Chapter 14Organometallic Compounds Dr. Wolf's CHM 201 & 202 14-1

  2. 14.1Organometallic Nomenclature Dr. Wolf's CHM 201 & 202 14-2

  3. Li H2C CHNa Cyclopropyllithium Vinylsodium CH3CH2MgCH2CH3 CH3MgI Diethylmagnesium Methylmagnesiumiodide Metal is the parent Dr. Wolf's CHM 201 & 202 14-3

  4. 14.2Carbon-Metal BondsinOrganometallic Compounds Dr. Wolf's CHM 201 & 202 14-4

  5. Electronegativities 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 Dr. Wolf's CHM 201 & 202 14-5

  6. R X R X Polarity of Bonds organometallics are a source of nucleophilic carbon d+ d– d– d+ Dr. Wolf's CHM 201 & 202 14-6

  7. Polarity of Bonds CH3F CH3Li Dr. Wolf's CHM 201 & 202 14-7

  8. 14.3Preparation of Organolithium Compounds Dr. Wolf's CHM 201 & 202 14-8

  9. R X + 2Li R Li + LiX Organolithium Compounds normally prepared by reaction of alkyl halides with lithium An oxidation-reduction reaction: carbon is reduced same for Ar—X Dr. Wolf's CHM 201 & 202 14-9

  10. Examples diethylether (CH3)3CCl + 2Li (CH3)3CLi + LiCl –10°C (75%) diethylether Br + 2Li Li + LiBr 35°C (95-99%) Dr. Wolf's CHM 201 & 202 14-10

  11. [R X] R X + Li • • R Li X– • • Electron Bookkeeping + Li+ •– • Li• + R• Dr. Wolf's CHM 201 & 202 14-11

  12. 14.4Preparation of Organomagnesium Compounds: Grignard Reagents Dr. Wolf's CHM 201 & 202 14-12

  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 Dr. Wolf's CHM 201 & 202 14-13

  14. Cl MgCl Examples diethylether + Mg –10°C (96%) diethylether Br + Mg MgBr 35°C (95%) Dr. Wolf's CHM 201 & 202 14-14

  15. [R X] R X + Mg • Mg+ • • • R Mg+ X– X– • • • Electron Bookkeeping • • + Mg+ •– • + R• Dr. Wolf's CHM 201 & 202 14-15

  16. Order of Reactivity I > Br > Cl >> F RX > ArX Dr. Wolf's CHM 201 & 202 14-16

  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 Dr. Wolf's CHM 201 & 202 14-17

  18. Forbidden Groups Anything with an OH, SH, or NH group i.e. an acidic hydrogen therefore cannot use H2O, CH3OH, CH3CH2OH, etc. as solvents cannot prepare Grignard reagent from substances such as HOCH2CH2Br, etc. Dr. Wolf's CHM 201 & 202 14-18

  19. 14.5Organolithium and Organomagnesium Compounds as Brønsted Bases Dr. Wolf's CHM 201 & 202 14-19

  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– •• •• Dr. Wolf's CHM 201 & 202 14-20

  21. Example water is a stronger acid than butane + H2O CH3CH2CH2CH2Li CH3CH2CH2CH3 + LiOH (100%) Dr. Wolf's CHM 201 & 202 14-21

  22. Example methanol is a stronger acid than benzene + CH3OH MgBr + CH3OMgBr (100%) Dr. Wolf's CHM 201 & 202 14-22

  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. Dr. Wolf's CHM 201 & 202 14-23

  24. HC CH HC CMgBr Acetylenic Grignard Reagents are prepared by an acid-base reaction + CH3CH2MgBr stronger acid + CH3CH3 weaker acid Dr. Wolf's CHM 201 & 202 14-24

  25. 14.6Synthesis of Alcohols Using Grignard Reagents Dr. Wolf's CHM 201 & 202 14-25

  26. diethylether R C R O MgX •• •• •• R C OH •• •• Grignard reagents act as nucleophilestoward the carbonyl group d+ d– two-step sequence gives an alcohol as the isolated product C + MgX O •• – •• H3O+ Dr. Wolf's CHM 201 & 202 14-26

  27. Grignard reagents react with: formaldehyde to give primary alcohols aldehydes to give secondary alcohols ketones to give tertiary alcohols esters to give tertiary alcohols Dr. Wolf's CHM 201 & 202 14-27

  28. Grignard reagents react with: formaldehyde to give primary alcohols Dr. Wolf's CHM 201 & 202 14-28

  29. diethylether R C R + MgX O MgX •• •• •• R C OH •• •• Grignard reagents react with formaldehyde H product is a primary alcohol H H d+ d– H C O •• – •• H3O+ H H Dr. Wolf's CHM 201 & 202 14-29

  30. Cl MgCl H O C H CH2OH CH2OMgCl Example Mg diethylether H3O+ (64-69%) Dr. Wolf's CHM 201 & 202 14-30

  31. Grignard reagents react with: formaldehyde to give primary alcohols aldehydes to give secondary alcohols Dr. Wolf's CHM 201 & 202 14-31

  32. diethylether R C R + O MgX MgX •• •• •• R C OH •• •• Grignard reagents react with aldehydes H product is a secondary alcohol H R' d+ d– R' C O •• – •• H3O+ H R' Dr. Wolf's CHM 201 & 202 14-32

  33. H3C O C H CH3(CH2)4CH2CHCH3 CH3(CH2)4CH2CHCH3 OH OMgBr Example Mg CH3(CH2)4CH2Br CH3(CH2)4CH2MgBr diethylether H3O+ (84%) Dr. Wolf's CHM 201 & 202 14-33

  34. Grignard reagents react with: formaldehyde to give primary alcohols aldehydes to give secondary alcohols ketones to give tertiary alcohols Dr. Wolf's CHM 201 & 202 14-34

  35. diethylether R C R + MgX O MgX •• •• •• R C OH •• •• Grignard reagents react with ketones R" product is a tertiary alcohol R" R' d+ d– R' C O •• – •• H3O+ R" R' Dr. Wolf's CHM 201 & 202 14-35

  36. CH3 CH3 HO ClMgO Example Mg CH3Cl CH3MgCl diethylether O H3O+ (62%) Dr. Wolf's CHM 201 & 202 14-36

  37. 14.7Synthesis of AlcoholsUsing Organolithium Reagents Organolithium reagents react with aldehydes and ketones in the same way that Grignard reagents do. Dr. Wolf's CHM 201 & 202 14-37

  38. O CH H2C CHLi CHCH CH2 OH Example + 1. diethyl ether 2. H3O+ (76%) Dr. Wolf's CHM 201 & 202 14-38

  39. 14.8Synthesis of Acetylenic Alcohols Dr. Wolf's CHM 201 & 202 14-39

  40. HC CH HC CNa O C CH HO HC CNa Using Sodium Salts of Acetylenes NaNH2 NH3 1. NH3 + 2. H3O+ (65-75%) Dr. Wolf's CHM 201 & 202 14-40

  41. CH3(CH2)3C CH CH3(CH2)3C CMgBr 1. H2C O CH3(CH2)3C CCH2OH Using Acetylenic Grignard Reagents + CH3CH2MgBr diethyl ether + CH3CH3 2. H3O+ (82%) Dr. Wolf's CHM 201 & 202 14-41

  42. 14.9Retrosynthetic Analysis Retrosynthetic analysis is the process by which we plan a synthesis by reasoning backward from the desired product (the "target molecule"). Dr. Wolf's CHM 201 & 202 14-42

  43. C OH Retrosynthetic Analysis of Alcohols Step 1 Locate the carbon that bears the hydroxyl group. Dr. Wolf's CHM 201 & 202 14-43

  44. C OH Retrosynthetic Analysis of Alcohols Step 2 Disconnect one of the groups attached to this carbon. Dr. Wolf's CHM 201 & 202 14-44

  45. C Retrosynthetic Analysis of Alcohols OH Dr. Wolf's CHM 201 & 202 14-45

  46. MgX C O Retrosynthetic Analysis of Alcohols What remains is the combination of Grignard reagent and carbonyl compound that can be used to prepare the alcohol. Dr. Wolf's CHM 201 & 202 14-46

  47. CH3 CH2CH3 C OH O C CH2CH3 Example There are two other possibilities. Can you see them? CH3MgX Dr. Wolf's CHM 201 & 202 14-47

  48. O C CH2CH3 CH3 CH2CH3 C OH Synthesis Mg, diethyl ether CH3Br CH3MgBr 1. 2. H3O+ Dr. Wolf's CHM 201 & 202 14-48

  49. 14.10Preparation of Tertiary AlcoholsFrom Esters and Grignard Reagents Dr. Wolf's CHM 201 & 202 14-49

  50. •• diethylether OCH3 •• •• OCH3 R C R •• O MgX •• •• •• Grignard reagents react with esters R' R' d+ d– but species formed is unstable and dissociates under the reaction conditions to form a ketone C + MgX O •• – •• Dr. Wolf's CHM 201 & 202 14-50

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