Synthesis and characterisation of trialkylaluminium-dialkylamine adducts:: X-ray diffraction and 1H NMR studies

Trialkylaluminium-dialkylamine adducts of general formula (R3Al)-Al-1 . NHR22 (R-1 = Me, Et, Pr-i, Bu-i or Bu-t; R-2 = Me, Et, Pr-i or Bu-i) were synthesized by reacting (R3Al)-Al-1 and NHR22. at high temperatures these adducts either eliminate alkane, forming dimeric amides, or dissociate. Increase in the bulk of R-1 favours alkane elimination. In the H-1 NMR spectra of the complexes (R3Al)-Al-1 . NHEt2 the methylene protons of the ethyl groups exhibited non-equivalence, and the high-temperature coalescence of the methylene proton signals is due to exchange processes involving both the breaking and reforming of the Al-N dative bond, in a unimolecular or a bimolecular step. The free energy of activation for this process has been correlated to the bulk of the groups R-1. The crystal structures of Me3Al . NHMe2 and (Bu3Al)-Al-t . NHEt2 were determined and their molecular structures are discussed.