Aluminum-nitrogen rings and cages with organic handles: A theoretical study

The structures and stability of monomelic and oligomeric compounds resulting from the elimination of 2 mol of HBr from the AlBr₃en complex have been studied theoretically at the B3LYP/LANL2DZ(d,p) level of theory. Two series of the ring and cage oligomer compounds were considered: imino [AlBrNCH₂CH₂NH₂]_n, n = 1-4, 6 (I_n), and isomeric amido [AlBrNHCH₂CH₂NH] _n, n = 1-3 (A_n), species. In all cases the amido isomers are 95-295 kJ mol^-1 more stable compared to their imino counterpairs. Intramolecular donor-acceptor interactions play an important role in the stabilization of the structure. Possible pathways of the polymerization have also been explored. Although the generation of the oligomers via HBr elimination in the gas phase is predicted to be thermodynamically unfavorable, operation of such reactions in the condensed phase is feasible. Substitution of bromine by hydrogen makes H₂ elimination reactions thermodynamically favorable. This opens a perspective for the synthesis of novel ladder-type oligomers with a continuous (AlN)_n core supported by C₂H₄ balustrade and imino cages with C₂H₄ handles.