REACTIONS OF TRIS[BIS(TRIMETHYLSILYL)AMINO]ALUMINUM WITH AMMONIA AND PYROLYSIS STUDIES

[[(Me3Si)2N]2AlNH2]2 (1) and [[(Me3Si)2N]2Al(NH2)2]3Al (2) were prepared from reaction of ammonia with Al[N(SiMe3)2]3 in 1:1 and 1:2 mole ratios, respectively. The structures were established by molecular weight, NMR and infrared spectroscopy, and single-crystal X-ray diffraction analysis. [[(Me3Si)2N]2AlNH2]2: monoclinic, P2(1)/c, Z = 4, a = 9.162 (2) angstrom, b = 14.580 (3) angstrom, c = 34.444 (5) angstrom, beta = 94.94 (1)degrees, V = 4584 (2) angstrom 3. The structure shows the presence of a central, planar, approximately square, four-membered ring. Al(1)-N(1)-Al(2)-N(2) with Al(1)-N(1) = 1.944 (5) angstrom, Al(1)-N(2) = 1.926 (5) angstrom, Al(1)-N(1)-Al(2) = 95.3 (2)degrees, N(1)-Al(1)-N(2) = 84.2 (2)degrees. [[(Me3Si)2N]2Al(NH2)2]3Al: monoclinic C2/c, Z = 8, a = 25.993 (3) angstrom, b = 15.092 (2) angstrom, c = 41.084 (5) angstrom, beta = 107.49 (1)degrees, V = 15373 (4) angstrom 3. The structure features a central hexacoordinate Al atom joined to three tetracoordinate Al atoms by NH2 bridges. Thermolysis of 1 at 225-degrees-C gave pentane-soluble [(Me3Si)2NAlNH]4 characterized by mass balance data, molecular weight, and NMR and infrared spectroscopy. Pyrolysis of [(Me3Si)2NAlNH]4 both in vacuo and under ammonia failed to give pure AlN; silicon and carbon were retained. Thermolysis of 2 at 200-degrees-C resulted in a loss of 5HN(SiMe3)2; this process was unaffected by the presence of ammonia. Further pyrolysis in an inert atmosphere gave 6AlN.Si3N4; AlN was formed in ammonia.