Enantiomerically Pure Trinuclear Helicates via Diastereoselective Self-Assembly and Characterization of Their Redox Chemistry

A tris­(bipyridine)
ligand 1 with two BINOL (BINOL
= 2,2′-di­hydroxy-1,1′-binaphthyl) groups has been
prepared in two enantiomerically pure forms. This ligand undergoes
completely diastereo­selective self-assembly into D2-symmeteric double-stranded trinuclear helicates upon
coordination to copper­(I) and silver­(I) ions and to D3-symmetric triple-stranded trinuclear helicates upon
coordination to copper­(II), zinc­(II), and iron­(II) ions as demonstrated
by mass spectrometry, NMR and CD spectroscopy in combination with
quantum chemical calculations and X-ray diffraction analysis. According
to the calculations, the single diastereomers that are formed during
the self-assembly process are strongly preferred compared to the next
stable diastereomers. Due to this strong preference, the self-assembly
of the helicates from racemic 1 proceeds in a completely
narcissistic self-sorting manner with an extraordinary high degree
of self-sorting that proves the power and reliability of this approach
to achieve high-fidelity diastereo­selective self-assembly via
chiral self-sorting to get access to stereo­chemically well-defined
nanoscaled objects. Furthermore, mass spectrometric methods including
electron capture dissociation MSn experiments
could be used to elucidate the redox behavior of the copper helicates.