Regio- and diastereo-selective formation of dicopper(I) and disilver(I) double helicates with chiral 6-substituted 2,2 ': 6 ',2 ''-terpyridines

Two enantiomeric pairs of chiral terpy ligands (I and II; III and IV) beari ng enantiopure bornyloxy substituents at the 6-position were prepared in hi gh yield, stereoretentive reactions from (1R)-endo- or (1S)-endo- borneol; compounds I, II and III were structurally characterised. Dinuclear double h elicates were formed upon reaction with copper(I) salts, but solvent-depend ent and reversible formation of mononuclear or dinuclear double-helical com plexes was observed with silver(I) salts. The double helicates are formed w ith good to excellent diastereoselectivity for helical chirality. With thes e 6-substituted ligands, double helicates can exist as head-to-head (HH) or head-to-tail (HT) isomers; in solution, the HT isomers are favored, althou gh solid state interactions can overcome this preference.