Preparation and Stereochemistry of Cobalt(III) Complexes with S-Alkyl-l-cysteinate, N,N′-Trimethylenebis(S-methyl-l-cysteinate), and S,S′-Ethylene(or -Trimethylene)bis(l-cysteinate)

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Abstract
Five cobalt(III) complexes of [Co(terdentate-N,S,O)2] and [Co(sexidentate-N2,S2,O2)] types were prepared; here terdentate-N,S,O denotes S-ethyl-L-cysteinate (L-sec) and S-benzyl-L-cysteinate (L-sbc), and sexidentate-N2,S2,O2 denotes N,N′-trimethylenebis(S-methyl-L-cysteinate) (L,L-tbsmc), S,S′-ethylenebis(L-cysteinate) (L,L-ebc), and S,S′-trimethylenebis(L-cysteinate) (L,L-tbc). Three isomers, trans(S), trans(N), and trans(O), were chromatographically isolated for each of the bis L-sec and L-sbc complexes, while only the trans(O) isomer was isolated for each of the L,L-tbsmc, L,L-ebc, and L,L-tbc complexes. These isomers were characterized from their absorption, CD, and 1H and 13C NMR spectra. The trans(O) isomers of the bis type and L,L-tbsmc complexes, which were assigned to a mixture of R(S),R(S), R(S),S(S), and S(S),S(S) configurations concerning the coordinated sulfur atoms, showed a similar CD spectral behavior to each other in the whole region. The trans(O)-R(S),R(S) L,L-ebc isomer and trans(O)-S(S),S(S) L,L-tbc one showed characteristic absorption and CD spectral behavior in the sulfur-to-metal charge transfer band region.

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