SYM-[5.5.5]HETEROCYCLOPHANES - STRUCTURALLY WELL-DEFINED, MIXED PI HETEROATOM-DONOR MACROBICYCLIC CAGES/

Structural considerations for achieving conformational stability in cy clophanes are applied as design criteria in the synthesis of sym-[5.5. 5]triaza- and sym-[5.5.5]trioxacyclophane macrobicycles. These compoun ds act as dynamic hosts in which the metal ion migrates between equiva lent, C-3-related (eta(1)-C)(2)N-2 coordination sites. The metal-arene interaction may alternatively be described as three centre, two-elect ron sigma complexation to the C-H bond. Crystal structures of the copp er(I) and silver(I) complexes show that little reorganization is requi red on the part of the ligand to accommodate the metal, and the former provides an unusual, structurally characterized example of eta-bondin g of an arene to Cu-I.