MOLECULAR MECCANO .2. SELF-ASSEMBLY OF [ETA]CATENANES

The mutual molecular recognition between different: structural compone nts in large rings has led to the template-directed synthesis of a wid e range of catenanes composed of from two to five interlocked rings, T he molecular self-assembly processes rely upon the recognition between (i) pi-electron rich and pi-electron deficient aromatic units and (ii ) hydrogen bond donors and accepters, in the different components. In order to increase Our knowledge of the factors involved in such molecu lar self-assembly processes, a homologous series of [2]catenanes has b een constructed using macrocyclic polyethers of the bis(p-phenylene)-( 3n+4)-crown-n (n = 9-14) type as templates for the formation of the te tracationic cyclophane, cyclobis(paraquat-p-phenylene). Increasing the size of the tetracationic cyclophane to cyclobis(paraquat-4,4'-bitoly l) allows the simultaneous entrapment of two hydroquinone ring-contain ing macrocyclic polyethers affording a series of [3]catenanes, and one [4]catenane incorporating a cyclic dimer of the expanded cyclophane a nd three bis(p-phenylene)-34-crown-10 components. By analogy; increasi ng the number of hydroquinone rings in the macrocyclic polyether permi ts the self-assembly of more than one tetracationic cyclophane around the templates present in the macrocyclic polyether. In this context, t he template-directed synthesis of two [3]catenanes, incorporating two cyclobis(paraquat-p-phenylene) components and either (i) tris(p-phenyl ene)51-crown-15 or (ii) tetrakis (p-phenylene)-68-crown-20, has been a chieved and is reported. A combination of these two approaches has led to the successful self-assembly, in two steps, of a linear [4]catenan e, together with a small amount of a [5]catenane: The creation of thes e intricate molecular compounds lends support to the contention that s elf-assembly is a viable paradigm for the construction of nanometer-sc ale molecular architectures incorporating a selection of simple compon ents.