The absolute configurations and circular dichroism spectra of a series of cobalt(III) complexes containing a stereoselective quadridentate ligand

Abstract

A series of cobalt(III) complexes of the type [Co pep X₂]ⁿ⁺, [X = Cl^–, Br^–, NCS^–, NO₂^–, and H₂O; pep = the stereoselective quadridentate ligand L-(–)-1,8-diamino-1,8-dimethy-3,6-dithiaoctane] have been prepared. In all these complexes only the symmetrical cis-α-configuration of the ligand has been obtained and, in this configuration, the ligand is stereoselective to the extent of ca 65%. The absolute configurations of the series have been interconnected by chemical transformations and by n.m.r. spectroscopy, and provided an assumption is made about the stereoselective preference the absolute configurations of the two forms are established. The c.d. spectra are recorded and discussed. It has been found that, compared to previous observations, the present series of complexes show c.d. spectra which are apparently inconsistent with respect to both sign and intensity.