Structure of Triamidoaluminum Complexes:  A Theoretical ab Initio/IMOMM Study

Abstract

The electronic structure of three-coordinated complexes of aluminum Al(NR2)3 has been studied through theoretical calculations. In the unsubstituted system Al(NH2)3, ab initio calculations (MP2/6-31G(d,p) level) show that the optimal geometry results from a conrotatory motion of the three amido substituents starting from the fully conjugated planar species. The energy difference between these two structures is found to be small (less than 0.5 kcal/mol). In methylated species Al(NMe2)3, steric effects become important and the planar geometry is destabilized. The conrotatory geometry corresponds to the absolute minimum and is located 14.2 kcal/mol below the planar structure (MP2/6-31G(d,p) level). Several coupled motions of the amido substituents have been computed and have been found to stabilize the system with respect to the fully conjugated structure. A rough estimate of the steric repulsion is calculated by comparison between the unsubstituted and methylated species. Finally, the real molecules Al[N(SiMe3)2]3 and Al(NiPr2)3 have been studied through a coupled quantum mechanics/molecular mechanics method. In accordance with the experimental data, it is found that the conrotatory minimum is the absolute minimum in the R = SiMe3 case whereas a less symmetrical minimum is found in the R = iPr case. In this last minimum, an amido group is almost deconjugated and the two other groups move in a conrotatory manner. The different behavior of these two systems may originate from the quasi-spherical shape of the SiMe3 group, which leads to unavoidable steric repulsion.

Synthesis, Characterization, and Reaction of Aluminum Halide Amides Supported by a Bulky β-Diketiminato Ligand

“…The Al−N(1) and Al−N(2) bond lengths (1.891–1.929 Å) in 1 − 3 are close to the ones reported ,,, and obviously longer than the Al−N(3) distances (1.788–1.836 Å), resulting from the electronically delocalized β-diketiminato ligand. Furthermore, the Al−N(3) bond lengths in 1 − 3 increase with the steric demand of the amido substituents, which is in accordance with the trend in a previous theoretical study of the electronic structure of Al(NR 2 ) 3 (R = H, Me, i Pr, SiMe 3 ) . In each case of 1 − 3 , the N(3) atom favors a nearly trigonal coordination geometry because the sum of the angle at the nitrogen of the amido groups is very close to 360° ( 1 , 359.66°; 2 , 359.97°; 3 , 359.81°).…”

Amidoverbindungen von Aluminium und Gallium

“…Amidoverbindung des Aluminiums und des Galliums sind nicht nur aufgrund ihres synthetischen Potentials und der Einsatzmo È glichkeit in MOCVD-Prozessen [1, 2, 3 a] eine interessante Substanzklasse, sondern auch aufgrund des theoretischen Interesses an den Bindungsverha È ltnissen in der M±N-Bindung [4,5].…”

Tris(dialkylamino)aluminums: Syntheses, characterization, volatility comparison and atomic layer deposition of alumina thin films

“…From the atmospheric pressure thermogravimetric analysis (TGA, Figure 2) both precursors evaporate with onset temperatures of 200 °C and 150 °C for 1 and 2, respectively. Although counterintuitive since 1 is a liquid, it is believed to exist as a dimer in this phase but evaporates as the monomer requiring more energy to break its dimeric structure [10], [15] and [17]. This is unlike 2 which exists as a monomer, in both the solid and vapor phase [12].…”

“…their steric bulk should trigger the self-terminating paths and 2.) thermodynamics favor formation of an Al-O bond over the Al-N bond [15]. In addition, 1 and 2 show appreciable volatility (see below)-comparable to that of Al 2 (CH 3 ) 6 -and were successfully implemented in the growth of amorphous alumina using H 2 O as a coreactant.…”