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

The mutual molecular recognition between different: structural components in large rings has led to the template-directed synthesis of a wide range of catenanes composed of from two to five interlocked rings, The 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 molecular self-assembly processes, a homologous series of [2]catenanes has been constructed using macrocyclic polyethers of the bis(p-phenylene)-(3n+4)-crown-n (n = 9-14) type as templates for the formation of the tetracationic cyclophane, cyclobis(paraquat-p-phenylene). Increasing the size of the tetracationic cyclophane to cyclobis(paraquat-4,4'-bitolyl) allows the simultaneous entrapment of two hydroquinone ring-containing macrocyclic polyethers affording a series of [3]catenanes, and one [4]catenane incorporating a cyclic dimer of the expanded cyclophane and three bis(p-phenylene)-34-crown-10 components. By analogy; increasing the number of hydroquinone rings in the macrocyclic polyether permits the self-assembly of more than one tetracationic cyclophane around the templates present in the macrocyclic polyether. In this context, the template-directed synthesis of two [3]catenanes, incorporating two cyclobis(paraquat-p-phenylene) components and either (i) tris(p-phenylene)51-crown-15 or (ii) tetrakis (p-phenylene)-68-crown-20, has been achieved and is reported. A combination of these two approaches has led to the successful self-assembly, in two steps, of a linear [4]catenane, together with a small amount of a [5]catenane: The creation of these intricate molecular compounds lends support to the contention that self-assembly is a viable paradigm for the construction of nanometer-scale molecular architectures incorporating a selection of simple components.