Diene-dicopper

After treatment of zirconacyclopentadienes with 2 equivalents of CuCl at room temperature, the addition of a halogenating agent such as NBS at —78 °C leads to the formation of octatetraenes 57a [7m]. This reaction involves slow bromination of the diene-dicopper compounds and coupling with the alkenyl bromide moiety (Eq. 2.40). 

Although not completely characterized, this yellow solid was assumed to be a dicopper diene derivative. In order to dissolve the yellow precipitate, DMPU (dimethylpropylene urea) was required. The dicopper diene species 34a is unstable in solution and gradually decomposes to undefined compounds. Therefore, all reactions involving transmetalation to copper are performed in situ in a one-pot or one-step process. 

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