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

Trialkylaluminium–dialkylamine adducts of general formula R13Al·NHR22 (R1 = Me, Et, Pri, Bui or But; R2 = Me, Et, Pri or Bui) were synthesized by reacting R13Al and NHR22. at high temperatures these adducts either eliminate alkane, forming dimeric amides, or dissociate. Increase in the bulk of R1 favours alkane elimination. In the 1H NMR spectra of the complexes R13Al·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 R1. The crystal structures of Me3Al·NHMe2 and But3Al·NHEt2 were determined and their molecular structures are discussed.