Since 1973, we are interested in developing iron-catalyzed coupling reactions. It is a new field of investigation and the replacement of palladium or nickel by iron is of tremendous importance in regard to sustainable development.
The first preparative reaction that we have reported is the iron-catalyzed alkenylation of Grignard reagent. We have discovered that NMP has a considerable beneficial influence on such reactions.
This procedure was extended to enol phosphates.
It is especially interesting for the stereoselective preparation of various conjugated dienes and even trienes from the corresponding dienyl or trienyl phosphates.
The coupling of functionalized aryl Grignard reagents with alkenyl halides is another interesting extension of this iron-catalyzed procedure.
Grignard reagents are easily homocoupled in the presence of iron salts by using various oxidants such as 1,2-dihalogenoethanes or atmospheric oxygen. The reaction is efficient with simple or functionalized aryl Grignard reagents.
Our studies in this area led to a very novel iron-catalyzed oxidative aryl-alkyl coupling between an aromatic and an aliphatic organozinc reagent.
On the other hand, the alkylation of aryl and alkenyl Grignard reagents is very efficiently catalyzed by iron salts. We have shown that HMTA (hexamethylenetetramine), a new ligand is very efficient.
A new catalyst was disclosed, the complex (FeCl3)2(tmeda)3.