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Ionic Liquids for Main Group Catalysis

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Ionic Liquids for Main Group Catalysis DOCTOR OF PHILOSOPHY Ionic Liquids for Main Group Catalysis Brown, Lucy Award date: 2020 Awarding institution: Queen's University Belfast Link to publication Terms of use All those accessing thesis content in Queen’s University Belfast Research Portal are subject to the following terms and conditions of use • Copyright is subject to the Copyright, Designs and Patent Act 1988, or as modified by any successor legislation • Copyright and moral rights for thesis content are retained by the author and/or other copyright owners • A copy of a thesis may be downloaded for personal non-commercial research/study without the need for permission or charge • Distribution or reproduction of thesis content in any format is not permitted without the permission of the copyright holder • When citing this work, full bibliographic details should be supplied, including the author, title, awarding institution and date of thesis Take down policy A thesis can be removed from the Research Portal if there has been a breach of copyright, or a similarly robust reason. If you believe this document breaches copyright, or there is sufficient cause to take down, please contact us, citing details. Email: [email protected] Supplementary materials Where possible, we endeavour to provide supplementary materials to theses. This may include video, audio and other types of files. We endeavour to capture all content and upload as part of the Pure record for each thesis. Note, it may not be possible in all instances to convert analogue formats to usable digital formats for some supplementary materials. We exercise best efforts on our behalf and, in such instances, encourage the individual to consult the physical thesis for further information. Download date: 11. Oct. 2021 Ionic Liquids for Main Group Catalysis By Lucy Christabel Brown, MChem Presented to the School of Chemistry and Chemical Engineering The Queen’s University of Belfast in fulfilment of the requirements for the degree of Doctor of Philosophy The Queen’s University of Belfast September 2019 ACKNOWLEDGEMENTS Firstly, I would like to thank Dr Gosia Swadźba-Kwaśny for giving me the opportunity to pursue this research and for her constant support throughout my work. Her motivation, dedication and expertise has been a constant inspiration. I am grateful for your time, mentorship, guidance and constant encouragement. I would also like to thank Professor John Holbrey for many insightful comments and support during my work. Also for his patience and confidence as I struggled through synthesises of deuterated materials up until the moment the taxi left for the airport. I would also like to thank Dr Leila Moura for guidance in the lab, inspiring Schlenk line designs and support in every aspect of my work as I learned to be a researcher. I hope introducing you to underwater hockey may go some way to repaying my debt. Additionally I would like to thank Dr James Hogg for his mentorship, help and creative ideas over the course of this research. I am also grateful to Dr Nimal Gunaratne for many useful conversations on synthesis. I would like to thank Dr Karolina Matuszek for productive collaborative work from Poland and in Belfast and for providing reaction data. I would also like to thank Ruairi O’Donnell and Dr Nancy Artioli for assistance with the safe use of hydrogen. My sincere thanks go to Deborah Murray for her help in so many aspects of my time at QUILL, not least in planning the MSDG meeting in which she took her time to guide us through and made a success of despite simultaneously coordinating other events. Thank you also for the pens. I am grateful too to the technical staff at QUILL and QUB. In particular I would like to thank Richard Murphy for his help with NMR spectroscopy. My time in Belfast has been a brilliant period of my life and for this I am hugely indebted to so many people including James, Mark, Leila, Emily, Keith, Nicki, Rachel, Alice, Anne, Yoan, Jeni, Gareth, Eoghain, Oli, Natasha and Marty for their friendship and support. I would also like to thank the members of QUB underwater hockey for welcoming me and giving me a life outside of the lab. Finally I would like to thank my Mum, Dad, brother Ed, my partner Richard and the Grannies for their constant support, encouragement and patience during my research. i ABSTRACT Lewis acidic ionic liquids, in particular chloroaluminate systems, have been found to be very effective catalysts for reactions such as Diels-Alder and Friedel-Crafts, and made their way to pilot and industrial processes, including oligomerisation of olefins (DifasolTM by IFP) and refinery alkylations (IonikylationTM by PetroChina and ISOALKYTM by Chevron).1 Despite their popularity, this archetypal group of catalysts faces two key challenges: the use of an expensive organic cation which plays no role in the catalytic process and placing the Lewis acidic function on the chloroaluminate anion, which does not allow for further modification of catalytic activity. The first of the two shortcomings has been addressed in the Swadźba-Kwaśny group through the development of liquid coordination complexes (LCCs),2 eutectic mixtures formed of an organic donor and a metal halide. The work reported here begins with the development of LCCs containing a breadth of halometallate species, synthesised by combining AlCl3, GaCl3, InCl3, SbCl3, SnCl4, SnCl2, ZnCl2 or TiCl4 with either trioctylphosphine (P888) or trioctylphosphine oxide (P888O), through study of their speciation and quantification of their acidity using Gutmann acceptor numbers (Chapter 2).3 The second drawback of chloroaluminate ionic liquids (Lewis acidity placed in the chloroaluminate anion) was addressed by developing borenium ionic liquids, with Lewis superacidic borenium cation.4 These first generation borenium ionic liquids maintained the chlorometallate anion combined with borenium cation. This work takes the borenium ionic liquids further, delivering metal-free systems with one, well-defined acidity centre in the cations (Chapter 3). These metal-free borenium ionic liquids were subsequently combined with sterically-hindered phosphines, such as tris(tert-butyl)phosphine, and some had the capability for H2 splitting, acting as the first reported ionic liquids frustrated Lewis pairs (IL- FLPs). This was achieved by the combination of a catechol ligand, adding steric bulk to the borenium cation, the introduction of long-chain ligands to lower the melting point, and the use of non-coordinating anions to prevent their involvement in the reaction. Another strand of the FLP work explored the potential for “traditional” ionic liquids as solvents for FLP reactions (Chapter 5). A classic hydrogen activating FLP, t tris(pentafluoro)phenyl borane (BCF) and tris(tert-butyl) phosphine (P Bu3), was dissolved in a non-coordinating ionic liquid [C10mim][NTf2] and the addition of H2 showed that the FLP in ionic liquid was capable of activating H2. Further to this, the movement of the FLP components in ionic liquid was found to be restricted in comparison to in molecular solvents. This promoted the lifetime of the reactive precursor, the encounter complex. A fundamental ii study into a weakly-bound BCF/phosphine encounter complexes in both benzene and 5 [C10mim][NTf2] by neutron scattering was carried out and this is described in Chapter 4. The results of the neutron scattering suggested an interatomic P-B distance of ~8 Å which agrees with molecular dynamics simulations in the literature.6 A pre-requisite for this study was the synthesis of deuterated phosphines via a Grignard synthesis, also described in Chapter 4. iii TABLE OF CONTENTS 1 Introduction ...................................................................................................................... 1 1.1 Defining Acidity ....................................................................................................... 1 1.1.1 Historical Perspective ....................................................................................... 1 1.1.2 Lewis Acidity ................................................................................................... 2 1.1.3 Quantification Methods .................................................................................... 4 1.1.4 Superacidity ...................................................................................................... 7 1.2 The Boron Group and Borocations .......................................................................... 8 1.2.1 Elements of the Boron Group ........................................................................... 8 1.2.2 Borocations ....................................................................................................... 9 1.3 Lewis Acidic Ionic Liquids .................................................................................... 17 1.3.1 Historical Context ........................................................................................... 17 1.3.2 Chlorometallate Ionic Liquids ........................................................................ 18 1.3.3 Liquid Coordination Complexes (LCCs) ....................................................... 25 1.3.4 Ionic Liquids with Cationic Lewis Acids ....................................................... 30 1.4 Motivation for This Work ...................................................................................... 34 2 Liquid Coordination Complexes .................................................................................... 36 2.1 Experimental .........................................................................................................
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