Hydroalumination of nitriles and isonitriles

Hydroalumination of H 5 C 6 -C≡N with di(tert-butyl)aluminum hydride 1 or the corresponding diethyl compound 2 yielded the products tBu 2 Al-N=C(C 6 H 5 )H 3 and Et 2 Al-N=C(C 6 H 5 )H 4, respectively, both of which form dimers possessing Al 2 N 2 heterocycles with two exocyclic C=N double bonds. NMR spectroscopic data indicate the occurrence of cis/trans isomers in solutions of compound 4. The dimerization of the imide via Al-N interactions was prevented by employing the hydride [(Me 3 Si) 2 HC] 2 AlH 6 bearing the bulky bis(trimethylsilyl)methyl substituents. Its reaction with benzonitrile yielded the compound R 2 Al-N=C(C 6 H 5 )H(N≡C-C 6 H 5 ) 7 [R = CH(SiMe 3 ) 2 ], in which the coordinative saturation of the aluminum atoms was achieved by adduct formation with one molecule of the starting nitrile. In these cases the C≡N triple bond inserted completely into the Al-H bond of the hydride. In contrast, the reaction of tert-butyl isonitrile afforded the product tBu 2 Al-C(H)=N-C 6 H 5 8 by the insertion of its terminal carbon atom into the Al-H bond. Hence, it has a geminal arrangement of the aluminum and hydrogen atoms. Dimerization of 8 yielded a six-membered heterocycle. Hydroalumination does not occur upon treatment of the hydride 1 with trimethylsilylnitrile. Instead, the Si-CN bond was cleaved, and the aluminum cyanide (tBu 2 Al-C≡N) 4 9 was isolated in a high yield.