Formation and Reactivity of a Molecular Magnesium Hydride with a Terminal Mg-H Bond.

A complex featuring a terminal magnesium hydride bond supported by an NNNN macrocyclic ligand, [Mg{Me3 TACD⋅Al(iBu)3}H] (3), was formed from its labile Al(iBu)3 adduct. Use of Al(iBu)3 to block the amido nitrogen of the NNNN macrocyclic ligand was essential to prevent aggregation. The structurally characterized compound 3 reacted with BH3 to give the BH4 derivative, whereas Me3 SiCCH and PhSiH3 led to the corresponding acetylide and silyl derivative under H2 elimination. Pyridine is inserted into the MgH bond to give selectively the 1,4-dihydropyridinate.