The Reaction of cobalt (III) and cobalt (III) complexes with D1 - and tri - peptides

Abstract

A general synthetic route for the preparation of bis-dipeptidate cobaltate(III) complexes has been developed. These complexes are formed with a high degree of stereo-selectivity, the L-dipeptidide giving the L-dipeptidate cobaitate(III) complex. Exchange of the C-termina.l methylene protons was found to occur in D20 with added base. The extinction coefficients and peak positions for a series of dipeptides have been determined and, for the optically active dipeptides, the molar rotation. All complexes have similar visible spectra and the yield was found to decrease as the size of the side chain substituent of the dipeptide increased. A complicated series of acid and base catalysed reactions were found to occur for the bis-trigIycinato cobaItate(III) complexes. Although no solid derivatives could be prepared an attempt has been made to rationalise structures in terms of the observed reactions. The cobalt(III) complex of diethyIenetriamine and gIycyIglycine was prepared as the perchlorate salt and characterised. Exchange of the C-terminal methylene protons occurs in D20 on addition of base. The pk a was determined spectrophotometricaIIy to be 0.74± 0.30.