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Title: An active-template mechanistic approach to homo- and hetero-circuit [3]rotaxanes
Author: Neal, Edward Alexander
ISNI:       0000 0004 5991 4544
Awarding Body: Queen Mary, University of London
Current Institution: Queen Mary, University of London
Date of Award: 2015
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Although known to chemists for nearly a century, interlocked structures have only been synthetically accessible since the 1980s when 'passive template' methods allowed the pre-complexation of components to increase yields. 'Active template' methods, initially developed by the Leigh group in 2006, have resulted in even higher yields of rotaxanes - "interlocked structures formed of at least one macrocycle penetrated by at least one impassably-stoppered axle" - and a phenomenal surge in interest in their properties as a result of this increased availability. This first method adapted highly efficient 'click' methodology to give the Active Template Copper-Mediated Alkyne-Azide Cycloaddition reaction (AT-CuAAC) and is still the most used rotaxane-forming method today. In this work, I provide the reader with an overview of these mechanically-interlocked architectures from synthesis to application. Later work by the Goldup group showed that a smaller macrocycle could make [2]rotaxanes (one macrocycle, one axle) with complete efficiency compared to their larger forebears, while intermediate sizes gave incomplete conversion, with unused macrocycle unrecovered. In this investigation, I then identify a series of novel doubly-interlocked [3]rotaxane products from this reaction that explain the absence of unused macrocycle. I then explore the variation of conditions and show how these novel products are favoured by high temperatures and high catalyst loading in a non-coordinating solvent, whereas their yields are suppressed in low temperatures and catalyst loading in a co-ordinating solvent with base, giving up to quantitative [2]rotaxane formation. To provide a mechanistic rationale for the formation of these products I then assess the effects of stopper length, macrocycle structure and lithiation experiments on the ratio of the [2]- to [3]rotaxane. The results of the above allow me to derive a new mechanistic hypothesis when I then test in a series of experiments to form [3]rotaxanes with two rings differing in either structure, size or both. Finally, the design, synthesis and testing of a stopper developed and used by myself for the AT-CuAAC reaction is described such that where two macrocycles differ in size, the larger can only be held in a novel heterocircuit [3]rotaxane, produced in synthetically useful yields.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: rotaxanes