Redox-Triggered Helicity Inversion in Chiral Cobalt Complexes in Combination with H+ and NO3– Stimuli

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• 作者：Janusz Gregoliński ; Masahiro Hikita ; Tatsuya Sakamoto ; Hideki Sugimoto ; Hiroshi Tsukube ; Hiroyuki Miyake
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：January 19, 2016
• 年：2016
• 卷：55
• 期：2
• 页码：633-643
• 全文大小：777K
• ISSN：1520-510X

文摘

Three chiral ligands with variable denticity, H₂L2–H₂L4, conjugated by N,N′-ethylenebis[N-methyl-(S)-alanine] and an ortho-heterosubstituted aromatic amine, were newly synthesized as analogues of previously reported H₂L1. Four contracted-Λ_oxo cobalt(III) complexes [Co(L)]⁺ with left-handed helical structure of Λ₄Δ₂ configuration were prepared by one-electron oxidation of the corresponding contracted-Λ_red cobalt(II) complexes [Co(L)], which were generated from chiral ligands and Co(ClO₄)₂·6H₂O or Co(CF₃SO₃)₂·5.2H₂O in the presence of an organic base. Although the prepared cobalt(III) complexes were very inert and kinetically stable against protonation and NO₃^– complexation, cobalt(III) reduction in the presence of CF₃SO₃H and/or Bu₄NNO₃ allowed immediate changing of their three-dimensional structures from the contracted-Λ_oxo form to the extended-Λ [Co(H₂L)Y₂]ⁿ⁺ (Y = solvent and/or anion, n = 0–2) form with left-handed helicity or to the extended-Δ [Co(H₂L)(NO₃)]⁺ form with right-handed helicity via N– to O–amide coordination switching. Both extended forms were contracted to the original Λ_oxo form by oxidation of the cobalt(II) center in the presence of an organic base. Thus, redox reactions triggered dynamic helicity inversion of the chiral cobalt complexes, via multiple molecular motions consisting of relaxation/compression, extension/contraction, and helicity inversion motions in combination with deprotonation/protonation of amide linkages and NO₃^– anion complexation.