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Keywords:

  • Alanes;
  • Alcohols;
  • Amines;
  • Chlorine;
  • X-ray diffraction

Abstract

LiAlH4 and AlCl3 reacted in a ratio 1:3 to obtain Cl2AlH, which is stabilised by the addition of two equivalents of N-methylpiperidine (nmp) to form dichloroalane (1) as bis adduct of nmp. Compound 1 was allowed to react with 2,6-tBu-4-MeC6H2OH and HOcHex in a 1:1 ratio to get compounds 2 and 3, respectively. Cl2Al(2,6-tBu-4-MeC6H2O)(nmp) (2) is a monomer in which the central aluminium atom is tetracoordinate. Contrary to the parent compound 1, compound 2 is stabilised by only one nmp molecule. The larger bulk of the alkoxide in 2 prevents the second nmp molecule to reach the aluminium atom. Compound 3 crystallises as unique anionic tri-nuclear aluminium entity [Al3Cl6(OR)4] [nmp2H]+ with a protonated nmp as countercation. The lesser bulk of the cyclohexanolate leads to a higher oligomerisation of ROAlCl2 (R = cyclohexyl). When a relatively bulkier alcohol, 1-methylcyclohexanol, was allowed to react with mixtures of LiAlH4 and AlCl3 prepared in 1:1 and 1:3 ratios in solution, compounds 4 and 5, respectively, were obtained. Both compounds ((HClAlOR)2 (4) and (Cl2AlOR)2 (5), R = cHexMe-1)) are dimers with oxygen as bridging atom in the Al2O2 rings. All compounds 2, 3, 4, and 5 were structurally characterised by X-ray diffraction on single crystals.