Synthesis and Structures of Magnesium Tetrahydridoaluminates

The molecular structures of XMg(A1H 4 ) · 4 THF ( 1a, 2, 3a ) (X = A1H 4 , Cl, Br) have been determined by X‐ray structural analysis. Each compound possesses a hexacoordinated Mg center and AlH 4 − groups bound to this center via a single hydride bridge bond. Attempts to prepare ROMg(AlH 4 ) compounds were successful only for sterically demanding groups R (R = CMe 3 , CPh 3 , naph, mes, smes). The 2‐naphthoxy derivative 7 , a compound with the composition (naphO)Mg‐(AlH 4 ) · 2.5 THF, is a dimer with a central Mg 2 O 2 ring. One of its two AlH 4 − groups is terminally bound to one Mg atom, the other bridges the two Mg centers. This structure indicates how AlH 4 − transfer may occur from ROMg(AlH 4 ) compounds to form Mg(OR) 2 and Mg(AlH 4 ) 2 .