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Monomeric Alanes:  Synthesis, Structure, and Thermolysis of Mes*Al(H)N(SiMe3)2 and a One-Pot Synthetic Route to Mes*2AlH (Mes* = −C6H2-2,4,6-t-Bu3)

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journal contribution
posted on 11.04.1998, 00:00 by Rudolf J. Wehmschulte, Philip P. Power
The reaction of (Mes*AlH2)2 (Mes* = −C6H2-2,4,6-t-Bu3) with HN(SiMe3)2 affords the monomeric amidoarylalane Mes*Al(H)N(SiMe3)2, 1. This product can also be synthesized by the reaction of [Mes*AlH2]2 with LiN(SiMe3)2, which, in addition, yields the byproducts LiAlH2{N(SiMe3)2}2, 3, and Mes*H. Thermolysis of 1 at 175−180 °C affords three different the related and the imide [Mes*AlN(SiMe3)]n, 5. In addition, the previously reported monomeric alane Mes*2AlH was synthesized in ca. 70% yield by a one-pot reaction between LiMes* (generated in situ) and AlH3·NMe3. All products were spectroscopically characterized, and the structure of 1 was determined by X-ray crystallography. The Al−N distance (1.819(2) Å) in 1 is relatively long. However, it has a substantial, 18.5 kcal mol-1, Al−N rotation barrier which is attributed to steric congestion rather than Al−N π bonding.