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A Journey Into the Reactivity of Not So Frustrated Lewis Pairs

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A Journey Into the Reactivity of Not So Frustrated Lewis Pairs From Phosphinoboranes to Mercaptopyridines: A Journey into the Reactivity of not so Frustrated Lewis Pairs Thèse Étienne Rochette Doctorat en chimie Philosophiæ doctor (Ph. D.) Québec, Canada © Étienne Rochette, 2019 Résumé La catalyse est une des pierres d’assise de la chimie moderne. Elle permet de faire des transformations difficiles d’une manière efficace et sélective, rendant possible des voies de synthèse plus courtes qui permettent ainsi à l’industrie chimique des économies de temps et d’argent. Par conséquent, le développement de la catalyse est d’une grande importance. Dans les dernières décennies, la plupart des efforts ont été orientés vers l’utilisation de métaux de transition de la seconde et troisième rangée, une approche couronnée de succès. Cependant, la maturité de ce sous-domaine et les améliorations des méthodes de caractérisation et de modélisation ont encouragé les chercheurs académiques à explorer le potentiel d’autres éléments du tableau périodique pour la catalyse. Cette thèse explore la catalyse sans métal, ou comme nous aimons l’appeler, la chimie organométallique sans métal. Elle présente des avancées dans le domaine des paires de Lewis frustrées (PLFs), qui utilisent des molécules comportant des fonctions acide de Lewis et base de Lewis pour rendre possible des transformations qui ne le seraient pas en utilisant seulement l’une ou l’autre des fonctions. Le focus particulier du travail est de comprendre et d’exploiter la chimie des PLFs. Par conséquent, nous ne nous sommes pas limités à seulement une sous-classe de PLFs ni à une seule transformation chimique. Les sujets contenus dans la thèse sont diversifiés et incluent la réduction du CO2, la fonctionnalisation de liens C-H, la chimie des liens B-B, la chimie des liens B-S ainsi que des discussions plus fondamentales sur le futur de la catalyse utilisant les PLFs. iii Abstract Catalysis is one of the cornerstones of modern chemistry. It allows difficult transformations to take place in an efficient and selective manner, making possible the design of shorter synthetic pathways and saving the chemical industry time and money. Thus, the improvement of catalysis is of great importance. In the past decades, most efforts have been oriented toward the use of second and third row transition metals, an approach that has been very successful. However, the maturity of that sub- field and the improvement of characterization and modelization techniques have been leading academic researchers in exploring catalysis with other elements of the periodic table. This thesis explores metal-free catalysis, or as we like to call it metal-free organometallic chemistry. It presents advances in frustrated Lewis pair (FLP) chemistry, which uses molecules containing Lewis basic and Lewis acidic functions to access transformations that would not be possible using only one or the other. The focus of the work is mostly on understanding and exploiting FLP chemistry. Thus, we did not limit ourselves to some sub-class of FLP nor to only one transformation. The subjects contained in the thesis are quite diverse and include CO2 reduction, C-H bond functionalization, B-B bond chemistry, B-S bond chemistry as well as more fundamental discussions on future FLP catalysis development. iv Table of contents Résumé .............................................................................................................................. iii Abstract ............................................................................................................................... iv List of Figures ................................................................................................................... vii List of Schemes ................................................................................................................... x List of Tables .................................................................................................................... xii List of Abbreviations ....................................................................................................... xiii Remerciements ................................................................................................................. xiv Introduction ......................................................................................................................... 1 Green Chemistry ............................................................................................................................. 1 Catalysis .......................................................................................................................................... 3 Frustrated Lewis Pairs ..................................................................................................................... 6 A Brief History of FLP.............................................................................................................. 10 Details on the thesis content .......................................................................................................... 12 Literature overview of subjects discussed in the thesis ................................................................. 14 CO2 reduction ............................................................................................................................ 14 Csp2-H borylation ...................................................................................................................... 17 Diboranes .................................................................................................................................. 20 Methodology ................................................................................................ 22 1.1 Inert synthetic methods ..................................................................................................... 23 1.2 11B NMR spectroscopy ...................................................................................................... 26 1.3 Density functional theory .................................................................................................. 29 1.3.1 Theoretical background ............................................................................................. 29 1.3.2 Utilization of DFT in the work presented ................................................................. 30 Metal-free reduction of CO2: from phosphinoboranes to aminoboranes .... 34 2.1 Previous work on phosphinoborane FLP catalyzed reduction of CO2 .............................. 34 2.2 Aminoborane FLPs for the hydrogenation of CO2 ............................................................ 39 2.3 Aminoborane FLPs Exhibiting High Robustness and Reversible Formic Acid, Water and Methanol Cleavage ........................................................................................................................ 44 Metal-free Csp2-H borylation of heteroarenes............................................. 48 3.1 Improvements on the C-H borylation system .................................................................... 61 3.1.1 Initial objectives and ideas ........................................................................................ 61 3.1.2 Discovery of bench stable pre-catalysts .................................................................... 64 3.1.3 Derivatives comporting less hindered amino group .................................................. 69 3.1.4 Final attempts at improving the system ..................................................................... 74 v From alkyne hydrogenation to B-B bond formation ................................... 78 4.1 FLP catalyzed alkyne hydrogenation ................................................................................ 78 4.2 The discovery of the diborane (NMe2-C6H4-BH)2 ............................................................ 84 4.3 The reactivity of the diborane (NMe2-C6H4-BH)2 ............................................................. 95 FLP promoted intra-molecular Csp3-H bond cleavage and subsequent rearrangements................................................................................................................. 104 S-H bond borylation and the σ-bond metathesis ....................................... 119 Transfer borylation: from N/B to N/S ....................................................... 132 Conclusion ....................................................................................................................... 144 Perspectives ................................................................................................................................. 144 Final conclusion .......................................................................................................................... 149 Annexes – Experimental Section ..................................................................................... 151 Organization of the section ......................................................................................................... 151 General experimental .................................................................................................................. 151 Chapter 2 ..................................................................................................................................... 152 Chapter 3 ..................................................................................................................................... 155 Chapter 4 ....................................................................................................................................
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