Our group is the pioneer in the chemistry of organomanganese reagents. We have described the first preparative method to obtain organomanganese chlorides from the corresponding organomagnesium or lithium reagents by using the cheap soluble ate complex MnCl4Li2 (MnCl2•2LiCl) to perform the transmetallation Mg/Mn or Li/Mn.
The first preparation of functionalized organomanganese reagents was achieved according to this procedure.
Organomanganese reagents can also be prepared directly from manganese metal in the case of reactive organic halides. Thus, we have shown that allylic halides (Barbier reaction) and α-halogenoesters (Reformatsky reaction) react with nonactivated commercial manganese metal.
As described in the following scheme, various reactions, i.e. acylation, 1,2-addition, 1,4-addition, alkylation can be performed efficiently under mild conditions. The yields are generally excellent and, in all cases, the reactions are very chemoselective. Organomanganese reagents often compare favorably to the other organometallics especially for their chemoselectivity.
It is tempting to compare organomanganese reagents to “soft” Grignard reagents. However, they behave sometimes very differently. The substitution of ortho-chloroarylketones that takes place even at low temperature is a good example.