雑誌会（200115）回答_藤田

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

Janusz Gregoliński†, Masahiro Hikita†, Tatsuya Sakamoto†, Hideki Sugimoto†, Hiroshi Tsukube†⊥, and Hiroyuki Miyake*†

†Department of Chemistry, Graduate School of Science, and ⊥JST, CREST, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan

Inorg. Chem., Article ASAP

DOI: 10.1021/acs.inorgchem.5b01902

Publication Date (Web): January 5, 2016

Copyright © 2016 American Chemical Society

*E-mail: miyake@sci.osaka-cu.ac.jp. Fax/Tel: +81 6 6605 3124.

http://pubs.acs.org/doi/10.1021/acs.inorgchem.5b01902

Synopsis

Four chiral ligands conjugated by N,N′-ethylenebis[N-methyl-(S)-alanine] and an ortho-heterosubstituted aromatic amine were synthesized. 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.

Abstract

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-Λoxo cobalt(III) complexes [Co(L)]+ with left-handed helical structure of Λ4Δ2 configuration were prepared by one-electron oxidation of the corresponding contracted-Λred 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-Λoxo 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 Λoxo 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.