Organometallic compounds are as they sound a carbon containing molecule attached to a metal. The commonest metals are Mg, Li, Na, Hg, Cd and Zn.

Polarisation is apparent in the molecule:

R₂C^δ- M^δ+, it varies from a not very polar covalent system to almost fully ionised species.

R₂C ^- is called a carbanion. By definition, every carbanion possesses an unshared pair of electrons and is therefore a base. When it accepts a proton, it is converted into its conjugate acid.

The stability of the carbanion is related to the strength of the conjugate acid, the weaker the acid, the stronger the base and lower the stability of the carbanion. By stability we mean stability toward a proton donor: the lower the stability the greater likelihood the carbanion will pick up a proton from an available source.

Nomenclature:

Alkyl metal, e.g. tetraethyl lead; Alkyl metal salt e.g. ethyl magnesium bromide

Chemical properties

Characteristically, the reactions are of nucleophilic carbon regardless of whether the organometallic is ionised or not.

Most typically:

Reactions of Grignard reagents; RMgHal e.g. EtMgBr (ethyl magnesium bromide)

1 Et^- as a strong base, reacting with proton acids:

2 Reactions with electrophilic carbon:

a)

b)

c) Aldehydes and ketones.

Et^- with CH₂O 1^o alcohols CH₃CH₂OH

Et^- with RCHO 2^o alcohols CH₃CH₂(R)CHOH

Et^- with R₂CO 3^o alcohols CH₃CH₂(R)₂COH

d) Esters and acid chlorides (X=Chloride)

As you can see from the above examples once the Grignard reagent has been let lose it will continue to react to form the tertiary alcohol.

e) With carbon dioxide

Try to work out the mechanism for this reaction .

f) With Nitriles

In this reaction the ketone is produced because generally the Grignard reagent is destroyed before further reduction can occur.

The reaction goes via the imine R₂C=NH.

3 Reactions with other electrophiles.

a) With oxygen

b) With bromine

All acids have a conjugate base, and all bases have a conjugate acid.