Redox-Triggered Helicity Inversion In Chiral Cobalt Complexes In Combination With H+ And No3- Stimuli

Three chiral ligands with variable denticity, H(2)L2H(2)L4, 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-Delta(oxo) cobalt(III) complexes [Co(L)](+) with left-handed helical structure of Delta(4)Delta(2) configuration were prepared by one-electron oxidation of the corresponding contracted-Delta(red) cobalt(II) complexes [Co(L)], which were generated from chiral ligands and Co(ClO4)(2).6H(2)O or Co(CF3SO3)(2).5.2H(2)O 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-Delta(oxo) form to the extended Delta [Co(H2L)Y-2](n+) (Y = solvent and/or anion, n = 02) form with left-handed helicity or to the extended-Delta [Co(H2L)(NO3)](+) form with right-handed helicity via N to Oamide coordination switching. Both extended forms were contracted to the original Delta(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.