Active Magnesium from Catalytically Prepared Magnesium Hydride or from Magnesium Anthracene and its Uses in the Synthesis

Highly reactive, pyrophoric forms of magnesium with specific surface areas of 20–109 m 2 /g (Mg * ) can be generated by the dehydrogenation of catalytically prepared magnesium hydride (MgH 2 * ) or by decomposition of magnesium anthracene · 3 THF ( 4 ). The decomposition of 4 , with recovery of anthracene and THF, may be accomplished both thermally and by ultrasound in an organic solvent (toluene, n ‐heptane) or thermally in the solid state in vacuo. Mg * obtained by the latter method exhibits only weak reflections in the X‐ray powder diagram and has, in comparison to other mentioned Mg * species, the highest reactivity toward hydrogen. Diverse Grignard compounds can be prepared under mild conditions (⪕25°C) in THF or ether as well as in hydrocarbons by using Mg * from MgH 2 * from MgH 2 * or 4 . The cleavage of THF with formation of 1‐oxa‐2‐magnesiacyclohexane ( 2 ) is possible by employing Mg * from MgH 2 * or 4 .