New Developments in Activation of Magnesium

In the last two decades several new developments in the field of activated metals , also including magnesium, have been introduced. 

Varying claims have been made as to which of these techniques would be the easier or the more practical one unfortunately, all together, the number of investigations in which such activated forms of magnesium were used in the field of Barbier-type reactions is very limited indeed. 

Sonication. Sonication implies the use of ultrasound in chemistry and related disciplines. Only very recently has the first volume appeared of a research annual, reporting advances in sonochemistry [31]. 

Sonication was successfully introduced in organometallic chemistry in 1980 [32] when it was applied to Li-Barbier reactions (see Sect. 3.3.7, pp. 90-94) it was found that ultrasonic irradiation allows this reaction to be performed in wet technical grade THF. This compares well with the findings that freshly cut magnesium chips also react with haloalkanes in wet diethyl ether (see p. 170). 

The efficiency of sonochemical removal of adsorbed water and alcohol from magnesium surfaces was demonstrated [33] in the reaction of 2-bromopentane with this metal in diethyl ether when this solvent was half-saturated with water, an induction period of only 6-8 minutes was required before the reaction started. Without sonication it took 1-3 hours refluxing in the same solvent to get this reaction going. 

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