Reaction of the primary alane (2,4,6-t-Bu3H2C6AlH2)2 with nitriles, isonitriles, and primary amines

The reactions of the sterically encumbered primary alane (Mes*AlH2)(2) (Mes* = C6H2-2,4,6-t-Bu-3) with the nitriles t-BuCN, MesCN (Mes = C6H2-2,4,6-Me-3) or MeCN lead eventually to dimeric amido alane products in which one of the ortho t-Bu groups of the Mes* ligand is metalated and the nitrile is reduced to the amide ligand N(H)CH2R (R = t-Bu, Mes, or Me). The compounds [AlC6H2-2,4-t-Bu-2-6-CMe2CH2{mu(2)-N(H)CH2R}](2) (R = t-Bu, 2 (cis), 3 (trans); Mes, 4 (cis), 5 (trans); Me, 6 (cis)) have been isolated and characterized spectroscopically and also by X-ray crystallography in the cases of 4 and 5. The intermediate, dimeric iminato complex [Mes*Al(H){mu(2)-NC(H)t-Bu}](2) (1), can also be isolated under carefully controlled, mild conditions. Reaction of (Mes*AlH2)(2) with the isonitrile t-BuNC affords the cyclic species {Mes*AlN(t-Bu)CH2}(2) (7) featuring a six-membered (AlNC)(2) ring which, when heated, affords the cyclometalated species [AlC6H2-2,4-t-Bu-2-6-CMe2CH2{N(t-Bu)H}(CH2)](2) (8). Recognition that the products 2-6 and 8 were derivatives of primary amides led to an investigation of synthetic approaches to these product types via the direct reaction of (Mes*AlH2)(2) with some primary amines. Treatment of (Mes*AlH2)(2) with H(2)NCH(2)Mes affords the dimeric amido alane [Mes*(H)Al{mu(2)-N(H)CH(2)Mes}](2) as a mixture of trans (9) and cis (10) isomers. Further heating of 9 and 10 affords the ortho-metalated compounds 4 and 5. The reaction of (Mes*AlH2)(2) with H2NSiPh3 furnishes the bis amido aluminum compound Mes*Al{N(H)SiPh3}(2) (11) and [Mes*(H)Al{N(H)SiPh3}](2). The latter yields the dimeric imide {Mes*AlSiPh3}(2) (12) at elevated temperature.