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
✍ Scribed by Klaus Knabel; Ingo Krossing; Heinrich Nöth; Holger Schwenk-Kircher; Martin Schmidt-Amelunxen; Thomas Seifert
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 799 KB
- Volume
- 1998
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
Reactions of metallated nucleophiles M I Y [Y = OR, SR, NR 2 , of a systematic analysis of the bonding parameters determined for the tmp 2 AlY compounds, combined with a PR 2 , AsR 2 , CR 3 , Si(SiMe 3 ) 3 , R = organyl, H] with bis(2,2,6,6tetramethylpiperidino)aluminum halides [tmp 2 AlX, (X = Cl, quantum mechanical study on model compounds (H 2 N) 2 AlY, not only reveal the presence of a highly polar Al-N bond, but Br, I)] offer facile access to a variety of bis(amino)alanes of the type tmp 2 AlY. As indicated by 27 Al-NMR spectroscopy, at the same time rule out AlN-pp(π) bonding, in contrast to the situation in the analogous tmp 2 BY compounds. It is mass spectrometry and X-ray crystal structure determinations, all of these compounds are monomeric in the solid shown that the Al-N bond length depends on the acidic character of the protic species HY: the shorter d(Al-N), the state, in solution, and in the gas phase. Even Al-E single bonds (E = Si, P, As etc.) that are not commonly encountered less basic is Y. are stabilized by the supporting tmp fragments. The results Ge, SnϭSn [3] [4] [5] and IIIϪV (BϭN, BϭP, BϭAs) [6] [7] [8] is primarily determined by AlϪN bond polarity [15] . Howdoubly bonded systems. In the latter species, bond shortenever, no systematic analysis on the variation of AlϪN bonding and small twist angles between the planes at boron and ing parameters in a family of compounds has so far been the group-V elements are reported, indicative of pp(π) interperformed. We found that bis(tetramethylpiperidino)alanes actions. By means of variable-temperature 1 H-NMR specrepresent such a family. troscopy [9] and quantum mechanical calculations [10] , acti-Recently, we published the synthesis and structures of the vation barriers for rotation about the BϪE bond (E ϭ N, monomeric bis(2,2,6,6-tetramethylpiperidino)aluminum P, As) as high as 33 kcal/mol have been determined.
halides {tmp 2 AlX [X ϭ Cl (1a), Br (1b), I (1c)]} [16] , which allow even the synthesis of transition-metal compounds Considering the heavier homologues of boron, i.e. aluminum and gallium, these might also be capable of adopting such as [tmp 2 AlϪFe(cp)(CO) 2 ,] (2) [17] . Here, we report on a variety of additional derivatives of bis(tmp)alanes. The such bonding arrangements. However, no compounds containing AlϭP or AlϭAs double bonds have yet been compounds 1a؊c, 2, and of the type tmp 2 AlY 3؊6 {Y ϭ OR, SR, NR 2 , PPh 2 , AsPh 2 , CR 3 , Si[Si(Me) 3 ] 3 , R ϭ or-characterized. Thus, the gallyl phosphide tBu 2 GaP(Mes)-(SiPh 3 ) exhibits a barrier to rotation about the GaϪP bond ganyl, H} possess tricoordinated aluminum and nitrogen centers. To allow a distinction to be made between possible of only 12.7 kcal/mol [11] . Taking this result, together with an almost planar (sum of bond angles 346.2°) geometry at pp(π) interactions, N(p)AlX(σ*) interactions and a highly polar bonding situation at the aluminum center [χ(N) ϭ the phosphorus atom and a short GaϪP bond length, the authors concluded that a small pp(π) contribution might be 3.1; χ(Al) ϭ 1.6; Pauling electronegativity], the structures of these compounds were determined in the solid state. Sys-present [11] . In the case of aluminum amides, pp(π) interaction, well established for the homologous aminobor-tematic variation of the group Y not only changes the electronic situation at the aluminum atom, but Ϫ since the am-anes [6] [9] , has been used to explain short bond lengths in