Spring 2011Dr. Halligan CHM 236 Organometallic Compounds Chapter 11

Ch. 11 Overview Organolithium and Grignard Reagents Coupling reactions with Gilman reagents Palladium-Catalyzed Coupling reactions including the Suzuki and Heck Alkene Metathesis: Reactions with Grubb’s and Schrock’s catalysts

3

4 Organometallic Compounds An organic compound containing a carbon–metal bond Organolithium compounds and organomagnesium compounds are two of the most common organometallic compounds

5 Preparation of Organolithium Compounds

6 Preparation of Organomagnesium Compounds

7

8 Alkyl halides, vinyl halides, and aryl halides can all be used to form organolithium and organomagnesium compounds However, these organometallic compounds cannot be prepared from compounds containing acidic groups (OH, NH 2, NHR, SH, C=CH, CO 2 H) Let’s draw a reaction to show how this happens:

9 Coupling Reactions Preparation of the Gilman reagent: Example of carbon–carbon formation using the Gilman reaction:

10 Gilman reagents can be used to prepare compounds that cannot be prepared by using nucleophilic substitution reactions: Why can’t these compounds be prepared by S N 1 or S N 2 reactions?

11 Gilman reagents can replace halogens in compounds containing other functional groups:

12 The Heck Reaction

13 The Stille Reaction

14 The Suzuki Coupling

15 Mechanism of the Suzuki Coupling Reaction Oxidative addition: Pd (0) to Pd (II):

16 Hydroxide exchange:

17 Transmetallation: Reductive elimination:

18 Mechanism of the Heck Coupling Reaction Oxidative addition: Pd (0) to Pd (II):

19  Complex formation: Insertion:  complex  complex

20 Elimination: Trans stereochemistry Regeneration of the catalyst: Undergoes oxidative addition to bromobenzene