Mechanical Activation of Organocatalysts

Abstract

Mechanical force has long been used for activating chemical reactions. With research carried out into how mechanical force can be transduced on a macromolecular level using polymer chains, mechanochemistry is fast becoming a field of incredible importance. The development of mechanophores, small molecules that are specifically designed in such a manner that they can respond in a desired manner to the application of force, has vastly increased the scope of which the field can be applied to practical uses. Specifically, the development of self-healing materials is a subject that can benefit from such chemicals. The idea of implementing mechanophores into materials that, upon application of force through physical manipulation, would lead to a useful species is one that would be highly useful in a material for this purpose. Mechanocatalysts are one such prospect where the latent mechanophore forms an active catalyst upon cleavage; if this catalyst could then be responsible for the regeneration of a material we would have an autonomic healing system. Though mechanocatalysts have been previously reported, there are only a few select examples to be found and all of them share the same basic design of a metal centre with a weak coordinate bond that can be exploited. We investigated in this work the idea of developing purely organic mechanocatalysts, focussing primarily N-heterocyclic carbenes along with a trityl carbocation, in order to alleviate issues of cost, toxicity and environmental damage associated with metal-based compounds that would hinder their implementation into materials. We have documented the difficulties encountered and our attempts to overcome then during the design, synthesis and testing of these species. Additionally, and most importantly, we have shown how an in-depth investigation into the cleavage of a specific mechanophore system revealed a phenomenon in which three concomitant pathways were observed that we could control through the mechanophore design.

Date of Award	31 Dec 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Michael Turner (Supervisor) & Guillaume De Bo (Supervisor)