OPTICALLY-ACTIVE TRIS]DITHIOCARBAMATO)COBALT(III) CHELATES - PREPARATION AND ASSIGNMENT OF ABSOLUTE-CONFIGURATION

A series of optically active tris(dithiocarbamato)cobalt(III) complexes, Co(R2(dtc))3 (R=Me; Et; i-Pr; n-Bu; i-Bu; pyrrolidyl; morpholyl; phenyl; benzyl; t-Bu, CH2CH2OH), has been prepared by a ligand-relacement reaction of the optically active cobalt complexes of ethylenediaminetetraacetic acid, (+)546-K[Co(EDTA)]-2H2O, 1, 2-propanediaminetetraacetic acid, (+)546-K[Co((-)-PDTA)]-3H2O, and ethylenediaminedisuccinic acid, (+)546-Na[Co(EDDS)]-H2O, with the sodium salt of the appropriate dithiocarbamate in aqueous or aqueous/acetone media. The partially resolved optically active Co(R2(dtc))3 complexes are precipitated in high yield. The absolute configuration of the compounds is deduced from the sign of the circular dichroism band in the visible spectral region arising from the 1A1→1Ea transition in D3 symmetry. Those species which exhibit a negative CD band in chloroform solution are assigned the A absolute configuration. The peak profile and position of the CD spectrum is little affected by solvent interactions. When established structural features of the starting materials are considered, certain steric effects are seen to be important in directing the course of replacement of the chiral hexadentate ligand. Such effects are most evident in the reactions involving the (+)546-[Co((-)-PDTA)]- anion where the equatorial methyl group has a strong nonbonded interaction with the incoming R2(dtc)- ion for all R substituents. The compounds prepared in this reaction show negative CD bands for the 1A1→Ea transition and have the A absolute configuration. The absolute configuration of the active Co(R2(dtc))3 compounds prepared from the (+)546-[Co(EDTA)]- and (+)546-[Co(EDDS)]-ions is dependent on the R substituent, particularly where R is a bulky group such as i-Pr. In these cases there are appreciable nonbonded interactions with the chiral ligand during its displacement, and both Δ and A forms are isolated depending on the R substituent of the dithiocarbamate. © 1979, American Chemical Society. All rights reserved.