Synthesis, characterisation and a theoretical investigation of the formation of lithium dialkylaluminium amides

Reaction of the pre-formed crystalline amides [(PhCH2)(2)NLi] and [Me2AlN(CH2Ph)(2)] in the presence of pyridine results in the formation of the mixed metal complex [Me2Al{(PhCH2)(2)N}(2)Li . pyr] 1. Ab initio molecular orbital calculations indicate formation of the bimetallic product is energetically favourable. Using single crystal X-ray analysis for 1 and the pyridine solvate [{(PhCH2)(2)NLi . pyr}(2)] 7, in combination with theoretical calculations, the possible driving forces for the reaction are discussed. A major contributing factor in the stabilisation of the bimetallic compound was found to be a reduction in steric crowding in the mixed metal base compared to the homometallic dialkylaluminium amide. In addition, complex 1 shows significant benzyl to lithium interactions which contribute to the overall bonding. Such interactions are unusual in that donor solvent is present as competing complexant. (C) 1999 Elsevier Science S.A. All rights reserved.