QUANTUM SEMIEMPIRICAL STUDY ON THE REACTIVITY OF SILYLATED DIAMINES IN THE SYNTHESIS OF AROMATIC POLYAMIDES

The reasons for the reactivity increase toward acyl chlorides caused i n aromatic amines by silylation are studied by quantum semiempirical a nd ab initio methods. Silylated amino groups adopt an sp(2) planar geo metry, in contrast to that observed in the unsilylated series, where a partially pyramidal structure intermediate between sp(3) and sp(2) ge ometry was obtained. Silylation also causes a strong increase of elect ronic density on the amine nitrogen and an increase of the Highest Occ upied Molecular Orbital (HOMO) energy, both effects favoring the highe r reactivity of these silylated amines. In addition to that, silylatio n produces a decrease of the activation energy in the reaction with an acyl chloride, relative to the unsilylated amines, thus increasing re action rate.