Stereoselective Formation and Chemical Properties of Chiral Polynuclear Complexes Depending on Oxidation Numbers

采用铂网工作电极的薄层石英电池，研究了s -桥接三钴（III）配合物[Co^<III>{Co^<III>(aet或L-cys)_3}_2]^<3+或3->]和二钴（III）配合物[Co^<III>{Co^<III>(aet或L-cys)_3}(dien)]^<3+或0> （aet = 2-氨基乙硫酸酯，L-cys = l -半胱氨酸，dien =二乙烯三胺）的紫外可见光谱电化学性质。三钴（III）配合物的吸收光谱电化学测量表明，aet配合物的双电子还原过程为Co^<III>Co^<III>Co^<III>→Co^<III>Co^<II>Co^<III>→Co^<III>Co^<II>Co^<II>，而L-cys配合物的双电子还原过程为伪一步。CD光谱电化学测量表明，aet三钴（III）配合物的旋光性异构体（ΔΔ形式）在单电子还原过程中失去手性，而L-cys三钴（III）配合物的Δ_<LLL>Δ_<LLL>异构体通过构型反转还原，形成Λ_<LLL>Λ_<LLL>异构体。Λ_<LLL>Λ_<LLL>同分异构体被还原并保留构型。aet和L-cys二钴（III）配合物通过电化学还原转化为相应的三钴（III）配合物，并伴有Co（II）离子和二氮配体的释放。还阐明了这种转换是在构型保留的情况下发生的。与各种金属离子和有机配体组成的多核配合物具有相似的性质和反应性。

The UV-vis spectroelectrochemical properties of S-bridged tricobalt(III) complexes [Co^<III>{Co^<III>(aet or L-cys)_3}_2]^<3+ or 3-> and dicobalt(III) complexes [Co^<III>{Co^<III>(aet or L-cys)_3}(dien)]^<3+ or 0> (aet = 2-aminoethanethiolate, L-cys = L-cysteinate, dien = diethylenetriamine) were investigated using a thin-layer quartz cell with a platinum mesh working electrode. The absorption spectroelectrochemical measurements for the tricobalt(III) complexes indicated that a two-electron reduction proceeds through pseudo two-steps, Co^<III>Co^<III>Co^<III>→Co^<III>Co^<II>Co^<III>→Co^<III>Co^<II>Co^<II> for the aet complex, while through pseudo one-step for the L-cys complex. The CD spectroelectrochemical measurements demonstrated that the optically active isomer (ΔΔ form) of the aet tricobalt(III) complex loses chirality during the one-electron reduction, whereas the Δ_<LLL>Δ_<LLL> isomer of the L-cys tricobalt(III) complex is reduced with an inversion of configuration, to form the Λ_<LLL>Λ_<LLL> isomer. The Λ_<LLL>Λ_<LLL> isomer is reduced with a retention of configuration. The aet and L-cys dicobalt(III) complexes were converted to the corresponding tricobalt(III) complexes by electrochemical reduction, accompanied by the release of the Co(II) ion and dien ligand. It was also elucidated that this conversion occurred with a retention of configuration.Similar properties and reactivities have been studied for the polynuclear complexes with various metal ions and organic ligands.