Nickel(II) complexes with unsymmetrical quadridentate Schiff bases having a pendant N-acyl substituent

Abstract

The condensation of N-acylated derivatives of o-aminocarbonyl aromatic compounds with the precursor 7-amino-4-methyl-5-azahept-3-en-2-one has been found to depend on the acidity of the amide proton and the nature of the substituent on the carbonyl carbon atom. Three new quadridentate Schiff-base ligands and their nickel(II) complexes having a pendant N-acetyl or N-trifluoroacetyl group have been obtained and characterized by spectroscopic techniques. A very unusual temperature-dependent proton NMR spectrum has been found for [4-methyl-9-(o-trifluoroacetylaminophenyl)-5,8-diazadeca-3,8-dien-2-onato(2–)]nickel(II) indicating a substantial energy barrier for enantiomer interconversion of the chiral complex molecule at moderate temperature. The crystal and molecular structure of this complex has been determined and shows that a fluorine–nickel interaction may be responsible for the inhibited enantiomer interconversion in N-trifluoroacetyl substituted nickel complexes. Crystallographic data: space group P2₁/c, a= 9.057(2), b= 13.769(4), c= 14.664(4)Å, β= 108.43(2)°, final R= 0.0434.