Carboxylate Ion dependency in the Cu(II) catalysed asymmetric Henry reaction: Structural characterisation of a tridentate Schiff Base complex containing a coordinated carboxylic acid


Akıncı A., Barut Celepci D., Alkan L. , Korlmaz N., Aygün M., Astley S. T.

Applied Organometallic Chemistry, cilt.31, ss.3831, 2017 (SCI Expanded İndekslerine Giren Dergi) identifier identifier

  • Cilt numarası: 31
  • Basım Tarihi: 2017
  • Doi Numarası: 10.1002/aoc.3831
  • Dergi Adı: Applied Organometallic Chemistry
  • Sayfa Sayıları: ss.3831

Özet

Six tridentate Schiff base ligands containing tertiary butyl or benzyl substituents were prepared from chiral amino alcohols and salicylaldehyde derivatives. The ligands were employed as catalysts for the Cu(II) catalysed asymmetric Henry reaction. It was discovered that when different carboxylate salts were used instead of copper acetate as the Cu(II) salt, significant changes in the enantioselectivity of the reactions were observed. Addition of Cu(OAc)2 to the ligand prepared from salicylaldehyde and α,α‐diphenyl‐tert‐leucinol resulted in the formation of dark green crystals. X‐ray structural analysis of these crystals showed that a square planar monomeric complex had been formed rather than the expected dimer. In the structure, the copper(II) centre is bonded to the tridentate ONO ligand and an acetate ion. There is a strong hydrogen bond between the protonated alcoholic oxygen of the Schiff base ligand and the uncoordinated acetate oxygen atom. These results, taken together, indicate that the carboxylate anion may be an important part of the active intermediate when this type of copper complex is used as a catalyst in the asymmetric Henry reaction.