Synthesis and Reactivity of Amidoaluminum Hydride Compounds as Potential Precursors to AlN

A new series of amidoaluminum hydride complexes H_nAl[N(SiHMe₂)₂]_3–nNMe₃ (1, n=2; 2, n=1), Al[N(SiHMe₂)₂]₃ (3), and [H₂AlN(SiHMe₂)₂]₂ (4) were prepared by the metallation of tetramethyldisilazane (Me₂HSi)₂NH with either H₃AlNMe₃ or H₃Al2OEt₂. The molecular structures of 1 and 2 were shown by X-ray crystal structure determination to be monomeric Lewis acid-base adducts with four coordinate aluminum centers and terminal amido groups. The molecular structure of 4 was found to be a dimer with bridging disilylamides in the solid state. Attempts to obtain crystals of [H₂AlN(SiMe₃)₂]₂, a bulkier analogue of 4, led to the isolation of the unusual alumoxane ²-(Me₃Si)₂ N-(AlH₂)₂-³-O-Al(H)N(SiMe₃)₂OEt₂ (6) in moderate yields. Thermolysis of 1 and 2 resulted only in the formation of ligand exchange and decomposition products, whereas thermolysis of 4 at 80°C afforded 1 equivalent of Me₂SiH₂ and a new species formulated as the imide complex [HAlNSiMe₂H]_n (7). Thermolysis of 4 in the presence of AlH₃NMe₃ gave Me₂SiH₂ and 7 at a higher reaction rate even at a lower temperature.