Syntheses and structural characterization of a LAl(N-3)N[mu-Si(N-3)(tBu)](2)NAl(N-3)L and a monomeric aluminum hydride amide LAlH(NHAr) (L=HC[(CMe)(NAr)](2), Ar=2,6-iPr(2)C(6)H(3))

Abstract

Reactions between the aluminum(I) monomer LAl (L = HC[(CMe)(NAr)](2), Ar = 2,6iPr(2)C(6)H(3)) and organic azides (RN3, R = C10H15 (adamantyl), Ph3Si; tBuSi(N-3)3) are reported. LAl reacted with the bulky azide RN3 in toluene in a temperature range of -50 to 25 degrees C, resulting in the compound LAl[(NR)(2)N-2] (R = C10H15 (1), Ph3Si (2)) instead of the expected Al=N multiple bond species, while the reaction with tBuSi(N-3)(3) gave LAl(N-3)N[(mu-Si(N-3)(tBu)](2)NAl(N-3)L (3). Compounds 1-3 have been fully characterized by mass spectrometry and IR and multinuclear NMR spectroscopy (H-1, C-13, and Si-29) as well as by single-crystal X-ray crystallography. The structural analysis of 1 and 2 reveals an AlN4 planar five-membered ring compound, suggesting a [2 + 3] cycloaddition of the Al=N multiple bond species with a molecule of RN3 despite the steric bulk of the L and R substituents. Compound 3 shows a bonding of the N3 group to the Al and a formation of the N2Si2 central core, implying the migration of N3 and a [2 + 2] cycloaddition in the reaction sequence. In addition, the solvent-free reaction of an aluminum dihydride LAlH2 with ArNH2 was also investigated at elevated temperatures (150-290 C), and a monomeric aluminum hydride amide, LAIH(NHAr) (4), was obtained as the only isolable product. The Al-H and N-H groups of 4 are shown in the IR and H-1 NMR spectra. The corresponding X-ray structural analysis exhibits the Al-H and N-H bonds that are nearly arranged in position trans to the Al-N-NHAr bond.