Redox-triggered chiroptical switching activity of ruthenium(III)-bis-(β-diketonato) complexes bearing a bipyridine-helicene ligand

The charged, electroactive bipyridine-helicene-ruthenium(III) complex [4]^.+,PF₆⁻ has been prepared from 3-(2-pyridyl)-4-aza[6]helicene and a Ru-bis-(β-diketonato)-bis-acetonitrile precursor (β-diketonato: 2,2,6,6-tetramethyl-3,5-heptanedionato). Its chiroptical properties (electronic circular dichroism and optical rotation) were studied both experimentally and theoretically and suggest the presence of 2 diastereoisomers, namely (P,Δ)- and (P,Λ)-[4]^.+,PF₆⁻ (denoted jointly as (P,Δ*)-[4]^.+,PF₆⁻) and their mirror-images (M,Λ)- and (M,Δ)-[4]^.+,PF₆⁻ ((M,Δ*)-[4]^.+,PF₆⁻). The electrochemical reduction of (P,Δ*)-[4]^.+,PF₆⁻ to neutral complex (P,Δ*)-4 was performed and revealed strong changes in the UV-vis and electronic circular dichroism spectra. A reversible redox-triggered chiroptical switching process was then achieved.