A Monomeric Aluminum Imide (Iminoalane) with Al–N Triple-Bonding: Bonding Analysis and Dispersion Energy Stabilization

The reaction of :AlAr iPr8 (Ar iPr8 = C6H-2,6-(C6H2-2,4,6- i Pr3)2-3,5- i Pr2) with ArMe6N3 (ArMe6 = C6H3-2,6-(C6H2-2,4,6-Me3)2) in hexanes at ambient temperature gave the aluminum imide Ar iPr8AlNArMe6 (1). Its crystal structure displayed short Al–N distances of 1.625(4) and 1.628(3) Å with linear (C–Al–N–C = 180°) or almost linear (C–Al–N = 172.4(2)°; Al–N–C = 172.5(3)°) geometries. DFT calculations confirm linear geometry with an Al–N distance of 1.635 Å. According to energy decomposition analysis, the Al–N bond has three orbital components totaling −1350 kJ mol–1 and instantaneous interaction energy of −551 kJ mol–1 with respect to :AlAr iPr8 and ArMe6N̈:. Dispersion accounts for −89 kJ mol–1, which is similar in strength to one Al–N π-interaction. The electronic spectrum has an intense transition at 290 nm which tails into the visible region. In the IR spectrum, the Al–N stretching band is calculated to appear at ca. 1100 cm–1. In contrast, reaction of :AlAr iPr8 with 1-AdN3 or Me3SiN3 gave transient imides that immediately reacted with a second equivalent of the azide to give Ar iPr8Al­[(NAd)2N2] (2) or Ar iPr8Al­(N3)­{N­(SiMe3)2} (3).