Nucleophilic Ring-Substitution Reactions of Unsymmetrical Quadridentate Schiff Base and Its Complex of Nickel(II) or Copper(II) with Ethyl Mercaptoacetate

Abstract

Abstract The nucleophilic replacement of halogen on the methine carbon of a Schiff base complex of nickel(II) or copper(II) by ethyl mercaptoacetate in dichloromethane proceeds via a four-centered intermediate, in which two polarizable atoms, such as bromine and sulfur, may stabilize strained bond angles. In the case of a free Schiff base ligand, a relatively stable adduct was spectrophotometrically confirmed. The adduct is thought to have a configuration analogous to that of a spiro compound containing a five-membered ring. Free ligands show no absorption bands in the wavelength region longer than 340 nm, while the adduct shows band at 375 nm assignable to a n-π* transition.