A Reactivity Study of Well-Defined Alkenylalanes Toward Anions, Lewis-Bases and Benzophenone

The reactivity of well-defined silyl-substituted alkenylalanes has been studied in the presence of anions, Lewis bases and benzophenone. In the presence of methyllithium or fluoride anions, the corresponding methyl- or fluoro-aluminates bearing alkenyl substituents of <i>Z</i> configuration have been fully characterized including by X-ray diffraction analysis. The configurational stability of these ate complexes toward <i>Z</i>-to-<i>E</i> isomerization revealed substituent-dependent and was examined on the basis of experiments and DFT calculations. In a second step, the fate of benzonitrile and ketone adducts of the alkenylalanes was investigated. Whereas the benzonitrile adducts revealed thermally stable, the corresponding Ph₂C═O → Al(alkenyl)₃ adducts evolved to the alkoxyaluminums due to the transfer of a α-hydride from an alkenyl substituent to the activated carbonyl function. The mechanism of this uncommon reduction could be unveiled and compared to more classical alkyl- and alkenyl-groups migration processes.