Synthesis and characterization of Tris[(S)-1-dithiocarboxypyrrolidine-2-carboxylato(2 -)-S,S']cobalt(III), a complex derived from the (S)-proline residue

Abstract

The ammonium salt of (S)-1-dithiocarboxypyrrolidine-2-carboxyic acid and its tris-chelated cobalt(III) complex have been prepared and characterized. The ammonium salt of the complex anion is soluble in water whereas the fully protonated form is soluble in some organic solvents. These diamagnetic cobalt(III) compounds and the corresponding neutral methyl ester complex are shown by ¹³C n.m.r. spectroscopy to have the facial geometrical structure.

The complex anion was successfully separated into diastereomeric Δ(SSS) and λ(SSS) forms (S refers to the asymmetric carbon atom in each of the proline moieties) by using Sephadex DEAE anion-exchange resin with aqueous ammonium chloride eluent. The more easily eluted species has the Δ absolute configuration at the dissymmetric cobalt atom as assigned from its circular dichroism spectrum.