Rational synthesis and dynamic studies of hetero[n]catenanes

Abstract

Catenanes are molecules that consist of mechanically interlocked macrocycles. The interlocked macrocycles are held by mechanical bond and can undergo large-amplitude motions with respect to each other. Thus, catenanes have found applications in molecular switches, sensors and machines etc. While the emergence of templated synthesis has provided an efficient way to obtain mechanically-bonded molecules, there is yet no reliable strategy to obtain high-order [n]catenanes. Studies of the dynamic properties and applications of catenanes are therefore largely limited to the simplest [2]catenane, and an efficient high order [n]catenane synthesis is necessary to bring catenane-based applications into next level of sophistication. In this thesis, the synthesis and dynamic studies of high order [n]catenanes are described. In Chapter 1, the topology and stereochemistry of mechanically interlocked molecules is introduced. Synthetic strategies of [n]catenanes and applications that exploit the dynamic properties of the interlocked components including molecular switches, catalysis, machines are highlighted. In Chapter 2, the high-yielding synthesis of a series of [3]catenanes, a [5]catenane and a [7]catenane featuring cucurbit[6]uril-mediated azidealkyne cycloaddition (CBAAC) and orthogonal β-CD/biphenylene template is described. The modulation of the dynamics of the interlocked β-CD in the [5]- and [7]catenanes in solvents of different polarity is also presented. In Chapter 3, the synthesis of a pair of [5]catenane and [4]catenane isomers with peripheral β-CD and CB[6] are described. Variable temperature 1H NMR and tandem MS studies revealed that the dynamics of the interlocked CB[6] and β-CD are dependent on both the sequences of macrocycle interlocking and the respective binding sites on the central macrocycles. In Chapter 4, the synthesis of a branched hetero[8]catenane is described. Variable temperature 1H NMR revealed that the dynamics of different types of interlocked macrocycles in the [8]catenane can be modulated separately by different stimuli, and that the effect from the macrocycle dynamics to the overall flexibility of the [8]catenane is in different extent due to the branched arrangement of interlocked macrocycles. In Chapter 5, a concluding remark is provided. In Chapter 6, experimental details and characterization data are presented.