Structure investigation of dimethyl-aluminium, -gallium and -indium O,O′-chelate complexes in solution and the solid state. Molecular structure of five-co-ordinated [Me2M(µ-OC6H4CO2Me-2)]2 adducts

Abstract

The reaction of trimethyl-aluminium, -gallium and -indium with an equimolar amount of methyl salicylate, 2-(HO)C₆H₄CO₂Me (Hmesal), gives [Me₂M(mesal)]_n chelate complexes in high yield (where n = 1 or 2, M = Al 1 or Ga 2; n = 2, M = In 3). The resulting compounds have been characterised in solution by NMR and IR spectroscopy as well as by cryoscopic molecular weight determinations in benzene; their molecular structures in the solid state were determined by single-crystal X-ray diffraction techniques. All three compounds are dimeric in the solid state, with five-co-ordinated metal centres. The deformation of the metal centre co-ordination sphere is discussed. In solution compounds 1 and 2 are monomeric, four-co-ordinated chelate complexes while 3 retains its dimeric structure. On the basis of the structural observation resulting from this study and with respect to related compounds the following sequence of the Group 13 metal centre Lewis acidity, in four-co-ordinated diorganometallic O,O′-chelate complexes is proposed: In  Al > Ga.