Mechanism of formation of Schiff base complexes. Part 3. Kinetic template effect of copper(II) in the condensation reaction of the salicylaldehydato-ion with a polyfunctional diprimary amine

Abstract

Under suitable experimental conditions the reaction of the salicyaldehydato-ion (sal) with diethylenetriamine (dien) in the presence of copper(II) takes place through a first-order kinetic process. The reactants are envisaged as being first co-ordinated to the copper(II), forming a labile ternary complex; interligand condensation is then supposed to occur within the co-ordination sphere of the metal. In the resulting reaction sequence the metal ion functions as a rudimentary enzyme. The dramatic difference between the activity of an ideal enzyme system, which reduces the order of a reaction by one unit through the rapid formation of a ternary complex, and that of the copper(II) ion, whrch through an analogous mechanism promotes the reaction of sal and dien, is interpreted on the basis of a perturbation from the optimum reaction geometry of the reactants by the co-ordination of the functional groups to the metal.