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

The reaction of :AlAriPr8 (Ar-iPr8 = C6H-2,6-(C6H2-2,4,6-Pr-i(3))(2)-3,5-Pr-i(2)) with (ArN3)-N-Me6 (Ar-Me6 = C6H3-2,6-(C6H2-2,4,6-Me-3)(2)) in hexanes at ambient temperature gave the aluminum imide (ArAlNArMe6)-Al-iPr8 (1). Its crystal structure displayed short Al-N distances of 1.625(4) and 1.628(3) angstrom with linear (C-Al-N-C = 180 degrees) or almost linear (C-Al-N = 172.4(2)degrees; Al-N-C = 172.5(3)degrees) geometries. DFT calculations confirm linear geometry with an Al-N distance of 1.635 angstrom. 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 :AlAriPr8 and (ArN)-N-Me6:. Dispersion accounts for -89 kJ mol(-1), which is similar in strength to one Al-N pi-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 :AlAriPr8 with 1-AdN(3) or Me3SiN3 gave transient imides that immediately reacted with a second equivalent of the azide to give (ArAl)-Al-iPr8[(NAd)(2)N-2] (2) or (ArAl)-Al-iPr8(N-3){N(SiMe3)(2)} (3).

Automated summary

This study identified the synthesis of aluminum imide and its crystal structure characteristics, revealing unique geometric and mechanical properties of the Al-N bond in aluminum imide. Through DFT calculations, energy decomposition analysis, and spectroscopic studies, a deeper understanding of the properties and interaction mechanisms of aluminum imide was achieved.