Synthesis and Stereoselectivity of Cobalt(III) Complexes of Quadridentate Ligands Possessing SNNS Array of Donor Atoms

Abstract

Abstract Several thiolato complexes of [Co(SNNS)(diamine)]+ type were prepared (diamine stands for en=1,2-ethanediamine, R-pn=(R)-1,2-propanediamine, and RR-chxn=(R,R)-1,2-cyclohexanediamine) and characterized from their visible–UV absorption, circular dichroism, and 13C NMR spectra, where SNNS denotes two kinds of open-chain quadridentate ligands, H2endet=3,6-dimethyl-3,6-diazaoctane-1,8-dithiol and R-H2pndet=(R)-3,4,6-trimethyl-3,6-diazaoctane-1,8-dithiol. Both the SNNS ligands gave the two geometrical isomers, cis-α(dark green) and cis-β(dark violet), whereas 3,7-dimethyl-3,7-diazanonane-1,9-dithiolate(2–) ligand gave no stable monomeric complex. Interestingly, stereoselective complex formation was found in Δ-cis-α-[Co(R-pndet)(en or RR-chxn)]+, Δ(SNRN)-cis-β-[Co(endet)(R-pn or RR-chxn)]+, and Δ(SNRN)-cis-β-[Co(R-pndet)(en or RR-chxn)]+, the Δ-cis-α configuration of the former complex being the novel one having the equatorially-oriented terminal chelate rings on the tertiary nitrogen atoms.