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 m2/g (Mg*) can be generated by the dehydrogenation of catalytically prepared magnesium hydride (MgH2*) 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 MgH2* from MgH2* or 4. The cleavage of THF with formation of 1‐oxa‐2‐magnesiacyclohexane (2) is possible by employing Mg* from MgH2* or 4.