An NMR Study of Metal Complexes Containing Acetylacetone and Related Compounds. IV. The NMR Spectra and the Ligand-exchange Reaction of Cobalt(III) Complexes Containing N,N′-Ethylenebis(acetylacetonimine) and Amino Acid

Abstract

Abstract A series of mixed cobalt(III) complexes with the general formula of K[Co(baen) (amino acid anion)2]·nH2O (baen=dianion of N,N′-ethylenebis(acetylacetonimine); amino acid = glycine, β-alanine, l-alanine, d-alanine, d,l-alanine, l-valine, d-valine d,l-valine, l-leucine, l-isoleucine, and l-phenylalanine) were newly prepared from a reaction mixture of trans-N,N′-ethylenebis(acetylacetoniminato)diaquocobalt(II), [Co(baen)(H2O)2], and the amino acids. Also prepared were mixed cobalt(III) complexes having the general formula of [Co(baen)(X)2]-ClO4(X=glycine ethyl ester, l-alanine ethyl ester, l-leucine ethyl ester, l-phenylethylamine, d-phenylethylamine, and d,l-phenylethylamine). From the elemental analyses, and the IR and NMR spectra, the amino acid anions were found to coordinate as a unidentate ligand, and the structures of all the complexes were determined to be trans with respect to the two nitrogen atoms of the coordinated amino groups. The NMR spectral behavior of the complexes containing d,l-amino acid anions and d,l-phenylethylamine was well interpreted in terms of the existence of the following three species in a relative ratio of 1:2:1; [Co(baen)(l-form ligand)2]±n, [Co(baen)(l-form ligand)(d-form ligand)]±n, and [Co(baen)(d-form ligand)2]±n. A rapid intermolecular exchange reaction of the apical amino acid anion groups was newly found in water: [Co(baen)(A)2]−+[Co(baen)-(B)2]−\ightleftharpoons2[Co(baen (A)(B)]− (where A and B indicate the apical amino acid anions). Also found was a rapid exchange reaction of the apical amino acid anion groups between the complex and free amino acid anion. Strong support for the rapid inter molecular exchange reaction was obtained in a CD spectral study of them.