A general and reliable method for the activation of Mg metal for the formation of various kinds of Grignard reagents has been developed. Utilizing DIBAL-H for the activation of the surface and drying of the reaction mixture the initiation of the Grignard reagent formation can be performed at or below 20 °C for aryl Grignard reagents. For alkyl bromides it is possible to activate the magnesium turnings at even lower temperatures. As the temperature is well below the boiling point of THF, it is possible to detect the initiation of the reaction through the temperature rise. The initiation method was found to be reliable also under very diluted reaction conditions as long as the reaction mixture was stirred. We have also shown that with this method it is possible to manufacture Grignard reagents well below the boiling point of THF.

Source: Organic Process Research & Development 2002, 6, 906-910. DOI: 10.1021/op025567.