Anuradha dubey deputy director vmou kota prof

MScCH-07 Vardhman Mahaveer Open University, Kota

University of Kota, Kota

Printed and Published on behalf of the Registrar, V.M. Open University, Kota.

Printed by :

MScCH-07

Vardhman Mahaveer Open University, Kota

Unit - 1

Organometallic Reagents-I

1.5.1 Oxidative- addition reaction

1.5.2Carbanion-halide exchange
1.5.3By vinyl halide

1

1.6.3 Addition with ketene and isocyanates

1.10References and Suggested Readings

1.0Principle of organolithium compounds

NMR studies also indicate that methyl lithium retains the tetrameric solid state structure in solution. The structures of (Li-R)4 units i.e tetrameric depicted by X-

2

It is an important method for the preparation of simplest organolithium reagents. The most important alkyl lithium reagent is butyl lithium. This method involves the oxidation of a metal M by the addition of a group R-X.

1.1.4 Metal hydrogen exchange reactions (Metallation)

1.1.7By reduction of sulphides

More stable carbanion due to OCH3

Organolithium derivatives are extremely reactive (super Grignard reagent). Organolithium compounds are oxygen and moisture sensitive and show Lewis acidic character.

Organolithium compounds are the most versatile reagents in all fields of chemistry . Thus some of the important applications of these compounds are as follows:

1.Organolithium compounds are highly reactive nucleophiles and strong bases due to the presence of strongly polarized Li-C bond.

5.Organolithium compounds can be used as powerful metallating agents.

1.4 Principle of organomagnesium halides

Fig.2 Structure of (a) Mg(Br)R(Et2O)2 , (b) [Mg(Br)Et(NEt3)]2 and (c)MgBr(Me)(THF)3

Grignard reagents are usually prepared by the action of organic halides and magnesium turnings in an ether solvent. This is the well known example of two electron oxidative- addition reaction.

8

1.6Properties of organomagnesium halides

9

1.6.6Nucleophilic substitution reactions at sp2 hybrid carbon
Grignard reagents react with acid chlorides, esters and lactones to give alcohols whereas Carbonates react with Grignard reagents to give esters.

Organomagnesium halides possess a variety of important applications some of which are as follows:

1.Grignard reagent is one of the most versatile reagents in organic and organometallic synthesis.

4.Grignard reagent provides a useful method for the preparation of t-alkyl amines like Me3C-NH2 , as such amines are not obtained from SN2 reaction between t-alkyl halides and ammonia.