Any Old Iron? Any Old Iron?

The reaction of Grignard reagents with alkyl halides is normally carried out with nickel catalysts (Kumada coupling). It has recently been shown by a number of groups in UK, France, Germany and Japan that iron catalysts can work well, but some workers have found that the results can depend on the quality of the iron, particularly when FeCl3 is used.

A recent report from the group of Cahiez at (CNRS, France) provides a text-book approach to sorting out the problem. They have now found that adding ligands such as TMEDA and HMTA (hexamethylene tetramine – a cheap industrial amine) leads to dramatic improvements, with best results when both amines are used (Cahier G et al Angew Chem Int Ed, 2007,46, 4364-4366). The results have been excellent, and one reaction was scaled to 0.25 mol.

\ FeCl3 can also be used as a catalyst. In fact a complex of FeCl3 and TMEDA is actually formed and can be isolated. This complex (FeCl3)2(tmeda)3 is, unlike FeCl3, not hygroscopic and can be stored at room temperature.



Trevor Laird