HELICITY INDUCTION IN HELICATE SELF-ORGANIZATION FROM CHIRAL TRIS(BIPYRIDINE) LIGAND STRANDS

The chiral tris- and pentakis(bipyridine) ligand strands 3a and 4 were synthesised, each in optically pure form with (S,S)-configuration. Ligand 3a yielded substituted double-helical metal complexes, derived from the parent trihelicate structure 2, with Cu(I) and Ag(I) ions. The spectral data, in particular the H-1-NMR spectra and the large positive Cotton effect, indicate that helicate formation occurs with very high induction of helicity. Together with consideration of the steric effects in the two possible helical diastereoisomers (P)-1 and (M)-1 that may be formed, the data favour the preferential generation of the right-handed double helicate (P)-1 from the tris(bipyridine) strand 3a of (S,S)-configuration.