Tetra- and octalactam macrocycles and catenanes with exocyclic metal coordination sites: versatile building blocks for supramolecular chemistry.

Abstract

The synthesis of a new tetralactam macrocycle and the simultaneous formation of catenanes and larger octalactam macrocycles is reported. These species bear 2,2'-biquinoline moieties suitably positioned to bind a metal center at the outer periphery of the macrocycles. (1)H NMR chemical shifts permit the unambiguous distinction of transoid and cisoid conformations of the biquinoline moiety, thereby allowing an unequivocal identification of the catenane and octalactam structures, despite the fact that both have the same elemental composition and bear identical structural subunits. With the aid of an anion template effect, rotaxanes can be prepared from the smaller tetralactam macrocycle. These reveal significantly altered requirements in terms of the stopper size as compared to previously reported tetralactam wheels. Several copper(I)-mediated dimers and a (bpy)(2)Ru(II) complex (bpy=2,2'-bipyridine) have been synthesized from the tetralactam macrocycle and the rotaxanes. The anion binding abilities of the tetralactam macrocycle and its (bpy)(2)Ru(II) complex in DMSO have been compared by (1)H NMR titration experiments, which revealed significantly enhanced binding by the metal complex. Mass spectrometry has been used to study the potential formation of larger assemblies of copper(I) and the catenane built-up from two tetralactam macrocycles. Indeed, a 2:2 complex was identified. In contrast, the octalactam macrocycle of the same elemental composition yields only 1:1 complexes, with the Cu(I) ion connecting its two biquinoline moieties in the center of a figure-eight-shaped molecule. Molecular modeling studies support the structural assignments made.