The aluminum-nitrogen bond in monomeric bis(amino)alanes. A systematic experimental study of bis(tetramethylpiperidino)alanes and quantum mechanical calculations on the model system (H2N)2AlY

Reactions of metalated nucleophiles M(I)Y [Y = OR, SR, NR2, PR2, AsR2, CR3, Si(SiMe3)3, R = organyl, H] with bis(2,2,6,6-tetramethylpiperidino)aluminum halides [tmp2AlX, (X = Cl, Br, I)] offer facile access to a variety of bis(amino)alanes of the type tmp2AlY. As indicated by 27Al-NMR spectroscopy, mass spectrometry, and x-ray crystal structure detns., all of these compds. are monomeric in the solid state, in soln., and in the gas phase. Even Al-E single bonds (E = Si, P, As etc.) that are not commonly encountered are stabilized by the supporting tmp fragments. The results of a systematic anal. of the bonding parameters detd. for the tmp2AlY compds., combined with a quantum mech. study on model compds. (H2N)2AlY, not only reveal the presence of a highly polar Al-N bond, but at the same time rule out AlN-pp(p) bonding, in contrast to the situation in the analogous tmp2BY compds. The Al-N bond length depends on the acidic character of the protic species HY: the shorter d(Al-N), the less basic is Y. [on SciFinder (R)]