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

Abstract

Trialkylaluminium–dialkylamine adducts of general formula R¹₃Al·NHR²₂ (R¹ = Me, Et, Prⁱ, Buⁱ or Bu^t; 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 Bu^t₃Al·NHEt₂ were determined and their molecular structures are discussed.