Manipulating cation Lewis acidity to create functional ionic liquid based systems

Abstract

This work focuses on designing new Lewis acidic (LA) cationic species for functional ionic‑liquid (IL) systems, with applications in intrinsically frustrated Lewis pairs (FLPs) for catalysis and in charge‑transfer (CT) materials.

Chapter 2 introduces a proof‑of‑concept intrinsic IL FLP formed from 2,6‑lutidine as the Lewis base (LB) and N‑methylacridinium bis(trifluoromethylsulfonyl)imide ([Me‑Ac][NTf₂]) as the LA cation. Comprehensive physical–chemical characterisation, including phase‑diagram analysis of mixtures and their hydrogen‑activation products, establishes the fundamental behaviour of this FLP system.

Chapter 3 presents neutron‑scattering studies of H/D‑isotopomeric 2,6‑lutidine/[Me‑Ac][NTf₂] mixtures to probe acid–base association and solvation structure. These measurements provide direct evidence for FLP encounter‑complex formation and offer insight into hydrogen‑activation pathways and proton/hydride transfer in IL environments.

Chapter 4 evaluates the catalytic performance of this IL FLP system for hydrogenation, dehydrogenation, and reduction of N‑benzylidene‑tert‑butylamine. These are the first demonstrations of ILs capable of generating intrinsic FLP catalytic sites, supported by systematic optimisation of reaction conditions.

Chapter 5 examines weaker LA ILs, [Cn₄CNPyr][NTf₂] (n = 1–4), as CT‑complex‑ forming liquids with 1‑methylnaphthalene, using electrochemical impedance spectroscopy to assess conductivity changes.

Chapter 6 outlines the synthesis of alternative [R‑Ac][NTf₂] ILs and related strong LA cations. 

Chapter 7 concludes with future research directions.

Thesis embargoed until 31st July 2027

Date of Award	Jul 2026
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Engineering and Physical Sciences Research Council
Supervisor	John Holbrey (Supervisor) & Gosia Swadzba-Kwasny (Supervisor)