Preparation and CD Spectra of Cobalt(III) Complexes with S-(Carboxymethyl)-l-cysteinate and Its Analogues

Abstract

Abstract Four cobalt(III) complexes of the [Co(l-quadridentate-N,S,O2)(en)]+ type were prepared; where l-quadridentate-N,S,O2 denotes S-(carboxymethyl)-l-cysteinate(l-cmc), S-(2-carboxyethyl)-l-cysteinate(l-cec), S-(carboxymethyl)-l-homocysteinate(l-cmhc), or S-(2-carboxyethyl)-l-homocysteinate(l-cehc). Each complex was chromatographically separated into the quasi-enantiomeric isomers; Λl-trans(O)-S(S) and Δl-cis(O)-R(S) for the l-cmc, l-cmhc, and l-cehc complexes, and Λl-trans(O)-R(S) and Δl-cis(O)-S(S) for the l-cec one. These isomers were characterized from their absorption and 13C NMR spectra. The sterically strained Δl-cis(O) isomers exhibited some significant CD spectral behavior in the first d-d absorption band region. The CD spectra are discussed in relation to the sizes of the S–N and S–O chelate rings joining the chiral sulfur atom in the l-quadridentate-N,S,O2 ligand.