Transmetallation with sonochemically prepared organometallics

160 Sprich, J.D. Lewandos, G.S. Inorg. Chim. Acta 1983,76, L241-L242. 

Zinc organometallics illustrate this methodology (see p. 347). Their one-step preparation from lithium, alkyl halides, and a zinc salt is easily accomplished. Alkyl, vinyl, or aryl reagents are obtained in short times and excellent yields. Sonication in a cleaning bath is sufficient to generate diarylzincs, but the probe technique is necessary in other cases, for unexplained reasons. A specific study in the cases of diheptyl and ditolyl zinc has shown that they are formed quantitatively with the proper technique in less than 30 min from the organic bromides, lithium and zinc bromide. 

Brown et ah discovered a simple preparation of organoboranes inaccessible by hydroboration, e.g., aromatic, benzylic, allylic, by sonication of the halides, most of the time bromides, with magnesium and trifluoroborane etherate. The Grignard reagent formed in situ undergoes metal exchange in high yields (Eq. 35). 70 

Different products are formed in diethyl ether and in THE, with an increased efficiency under sonication. The reaction applied to n-butyl bromide in ether gives tri-n-butylborane quantitatively, but the use of THF under identical conditions leads to an ate complex. The reactivity of the halides follows the normal sequence I Br Cl. Iodides give side reactions, making the use of bromides necessary. The metal of choice is magnesium, since lithium gives Wurtz-type products only. 

The direct access to organozinc reagents by sonication of the metal in the presence of various halides has been achieved successfully in a number of instances cited 

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