Novel properties of [2]catenanes

The lure of self-assembly lies in its capability to construct complex covalent molecular architectures with economies rivaling those of biological systems. Elucidation of these interactions is the basis of promising approaches to drug design, chromotography and new materials. A deeper understanding of self-assembly will therefore impact and cross-pollinate many fields in chemistry.; [2]catenanes have been earmarked to possess elements necessary as components in molecular devices. If they are to take hold and find applications then quantification of their dynamic processes is essential. This research takes steps to address both of these issues by assessing the nature and properties of self-assembling [2]catenanes using NMR spectroscopy and electrochemistry. Moreover, 2D exchange spectroscopy was used for the first time to acquire kinetic and thermodynamic data for the dynamic processes present.; The significance of the spacer unit between the two bipyridinium units in PX[2]catenane was investigated by systematically replacing the para-xylyl group with a diphenylmethane unit. The self-assembly of two novel [2]catenanes, PXD[2]catenane and BD[2]catenane was acheived, together with the assembly of their tetracationic components PXD cyclophane 2 and BD cyclophane 3.; Two dynamic processes were found operating within the [2]catenanes---circumrotation of the crown ether ring through the tetracationic cyclophane and rotation of the crown ether ring around the cyclophane. Evidence for a "twisting" and a "rocking" process in PX[2]catenane and a "pendulating" process in PXD[2]catenane was also found for the first time.*; The free energy barrier to circumrotation of the crown ether ring decreased from 15.6 kcal mol-1 in PX[2] catenane (354 K), to 10.1 kcal mol-1 in PXD[2]catenane (238 K). The barrier to rotation of the crown ether ring decreased from 12.4 kcal mol -1 in PX[2] catenane (258 K), through 11.7 kcal mol-1 in PXD[2]catenane (238 K), to 10.6 kcal mol-1 in BD [2]catenane (228 K). The rates of rotation of the crown ether ring around the cyclophane in PXD[2]catenane and BD[2]catenane, at room temperature, were extrapolated to be ca. 53 x 103 s-1 and 1700 x 103 s-1, respectively.; *Please refer to dissertation for diagram.