Synthesis of singly threaded high-order rotaxanes and investigation on their potential in radial high-order catenane assembly

Abstract

Mechanically interlocked molecules (MIMs) are molecules with molecular components interlocked via mechanical bond. Interlocked components in a MIM cannot be separated without the breaking of covalent bonds in the components, but relative motions among the interlocked components are possible by virtue of the lack of covalent connections among them. With a proper design of MIM, the co- conformational change can be triggered by a variety of physical and chemical stimuli, leading to a large amplitude molecular motion, to give stimuli-responsive MIMs for applications such as sensors, catalysts and new materials. In this thesis, the synthesis of a high-order rotaxane, and the attempt of using rotaxane as a precursor in the assembly of high-order catenane is described. In Chapter 1, an introduction on MIMs, their applications as sensors, catalysts and materials are described. A historical perspective on the synthetic strategies of catenanes, together with some recent examples of high-order catenane, are also discussed. In Chapter 2, the stereoselective synthesis of a high-order [6]rotaxane with five macrocycles interlocking onto an axle is described. The [6]rotaxane and lower-order rotaxane products have been characterized by NMR spectroscopy and ESI-MS. The shuttling of macrocycles along the axle was forced to be dependent on the occupancy of the axle by macrocycles. A rotaxane with a fully occupied axle has a relatively static structure when compared with its less congested derivative where dynamic shuttling was observed. Preliminary results on the assembly of a high-order catenane via cyclic oligomerization of a pseudo[4]rotaxane precursor is also discussed. The pseudo[4]rotaxane precursor, with three macrocycles interlocking onto an axle, were synthesized and characterized by NMR and ESI-MS. The assembly of high-order catenane from the rotaxane precursor and cis-protected square planar d8 metal complexes was attempted. Preliminary results from NMR and ESI-MS are discussed. In Chapter 3, synthetic procedures, together with NMR and ESI-MS spectra are included.