Borohydride reduction of azomethine bonds in β-alanine Schiff base complexes

Abstract

Borohydride reduction of the azomethine bond in the Schiff base complexes of β-alanine has been studied. Ni(II), Pd(II) and Pt(II) complexes of N-β-carboxyethyl-2-hydroxynaphthylideneimine (L¹H₂), N-β-carboxyethyl-2-hydroxybenzylideneimine (L²H₂), and N-β-carboxyethyl-N-2-hydroxynaphtylmethyleneamine (L3H₂) have been prepared. L¹H₂ forms complexes with palladium as Pd(L¹H)₂, in which carboxylic groups do not participate in the coordination. L²H₂ and L3H2 behave as tridentate double charged ligands, giving complexes of the type ML².nH₂O and ML³.nH₂O. Ni(II) gives binuclear complex [NiL³.2H₂O]₂. No visible reaction of –C=N- bond reduction with borohydride has been observed for the L¹H₂ complexes of Co(III) d⁶, Ni(II) d⁸, Pd(II) d⁸, Zn(II) d¹⁰ ions at 25ºС in dimethyl formamide. This tendency has also been observed for Ni(II) complex of salicylaldehyde based β-alanine Schiff base, L²H₂, as well as Ni(II), Pd(II), Zn(II) complexes of salen. However, the C=N bond can be reduced with borohydride when it coordinates the metal ions, Cu(II), Co(II) and Mn(II). Ni(II) complexes of both Schiff bases are inactive against reduction. The reduction rates of Schiff bases and related activation energies have also been determined.