Helical stereochemistry and chiral apple halves. 2. La coupe du roi via double helical complexation using oligo(bipyridine) strands and Cu(I)/Ag(I)

Oligo(bipyridine) strands and Cu(I)/Ag(I) form duplexes having a 2₁‐screw coincidental with a C₂‐axis. A segment containing a complete turn of the duplex can be considered to be a coupe du roi ensemble of two homochiral strands. Moreover, for D_2d symmetry monocationic Cu(I) complexes of bipyridine trimers and pentamers, addition of the requisite Cu(I) cations is a true chemical example of la coupe du roi. In this reaction, an achiral monocationic complex is converted into a multiple‐cationic duplex of two homochiral and homotopic 2₁‐helical halves. The chirality of the resulting duplex is a function of the particular set of bipyridine enantiotopic faces which are used for binding the additional cations. © 1993 Wiley‐Liss, Inc.