Preparation and Characterization of Iridium Hydride and Dihydrogen Complexes Relevant to Biomass Deoxygenation Jonathan M. Goldberg A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Washington 2017 Reading Committee: D. Michael Heinekey, Chair Karen I. Goldberg, Chair Brandi M. Cossairt Program Authorized to Offer Degree: Department of Chemistry © Copyright 2017 Jonathan M. Goldberg University of Washington Abstract Preparation and Characterization of Iridium Hydride and Dihydrogen Complexes Relevant to Biomass Deoxygenation Jonathan M. Goldberg Chairs of the Supervisory Committee: Professor D. Michael Heinekey Professor Karen I. Goldberg Department of Chemistry This thesis describes the fundamental organometallic reactivity of iridium pincer complexes and their applications to glycerol deoxygenation catalysis. These investigations provide support for each step of a previously proposed glycerol deoxygenation mechanism. Chapter 1 outlines the motivations for this work, specifically the goal of using biomass as a chemical feedstock over more common petroleum-based sources. A discussion of the importance of transforming glycerol to higher value products, such as 1,3-propanediol, is discussed. Chapter 2 describes investigations into the importance of pincer ligand steric factors on the coordination chemistry of the iridium metal center. Full characterization of a five-coordinate iridium-hydride complex is presented; this species was previously proposed to be a catalyst resting state for glycerol deoxygenation. Chapter 3 investigates hydrogen addition to R4(POCOP)Ir(CO) R4 3 t i R4 R4 3 [ POCOP = κ -C6H3-2,6-(OPR2)2 for R = Bu, Pr] and (PCP)Ir(CO) [ (PCP) = κ -C6H3-2,6- t i (CH2PR2)2 for R = Bu, Pr] to give cis- and/or trans-dihydride complexes. Two mechanisms of hydrogen addition are presented (concerted oxidative addition and proton-catalyzed addition); the mechanism of hydrogen addition is dependent on the steric environment at the metal center. Chapter 4 presents spectroscopic evidence for two new iridium-dihydrogen complexes only stable under high pressures of hydrogen (40-80 atm) and low temperatures. Furthermore, iridium- catalyzed isotope exchange between H2 and CD3OD is presented and its potential implications in supporting the glycerol deoxygenation mechanism. Chapter 5 outlines a fundamental reaction of oxidative addition of iodine to (tBu)4(POCOP)Ir(CO) complexes. Characterization of a cationic monoiodo iridium carbonyl complex as a potential oxidative addition intermediate is presented. TABLE OF CONTENTS Page List of Figures ................................................................................................................................iii List of Schemes ..............................................................................................................................vi List of Tables .................................................................................................................................vii Acknowledgments .......................................................................................................................viii Chapter 1: Introduction ..................................................................................................................1 1.1: Overview – Under vs. Overfunctionalized Chemical Feedstocks .................................1 1.2: Glycerol as a Chemical Feedstock ................................................................................2 1.3: Glycerol to 1,3-Propanediol ..........................................................................................3 1.4: Transition-Metal Catalyzed Conversion of Glycerol to 1,3-Propanediol ......................6 1.5: Dissertation Summary ................................................................................................10 1.6: Notes to Chapter .........................................................................................................10 Chapter 2: The Importance of Steric Factors in Iridium Pincer Complexes ............................12 2.1: Introduction ................................................................................................................12 2.2: Results ........................................................................................................................14 2.3: Discussion ..................................................................................................................31 2.4: Conclusion ..................................................................................................................40 2.5: Experimental ..............................................................................................................41 2.6: Notes to Chapter .........................................................................................................55 Chapter 3: Hydrogen Addition to (pincer)IrI(CO) Complexes ..................................................58 3.1: Introduction ................................................................................................................58 3.2: Results ........................................................................................................................61 3.3: Discussion ..................................................................................................................78 3.4: Conclusion ..................................................................................................................88 3.5: Experimental ..............................................................................................................89 3.6: Notes to Chapter .......................................................................................................101 Chapter 4: Detection of an Iridium-Dihydrogen Complex: A Proposed Intermediate in Ionic Hydrogenation .................................................104 4.1: Introduction ..............................................................................................................104 4.2: Results ......................................................................................................................106 4.3: Discussion ................................................................................................................120 4.4: Conclusion ................................................................................................................130 4.5: Experimental ............................................................................................................ 131 4.6: Notes to Chapter .......................................................................................................135 i Chapter 5: Oxidative Addition of Iodine to (tBu)4(POCOP)Ir(CO) Complexes .......................137 5.1: Introduction ..............................................................................................................137 5.2: Results and Discussion .............................................................................................139 5.3: Conclusion ................................................................................................................149 5.4: Experimental ............................................................................................................150 5.5: Notes to Chapter .......................................................................................................154 Bibliography ................................................................................................................................156 Appendix A .................................................................................................................................164 Appendix B ..................................................................................................................................166 Appendix C ..................................................................................................................................168 Vita ..............................................................................................................................................169 ii LIST OF FIGURES Page Figure 1.01. Polytrimethylene terephthalate (PTT) .........................................................................4 Figure 2.01. POCOP ligand framework .........................................................................................13 Figure 2.02. ORTEP of (tBu)2(OMe)4(POCOP)Ir(CO)(H)(Cl) shown with 50% thermal ellipsoids. Hydrogen atoms, except for the iridium-bound hydride, are omitted for clarity .......................................................................................................17 Figure 2.03. ORTEP of (tBu)2(diol)2(POCOP)Ir(CO)(H)(Cl) shown with 50% thermal ellipsoids. Hydrogen atoms, except for the iridium-bound hydride, are omitted for clarity .......................................................................................................17 Figure 2.04. ORTEP of (iPr)4(POCOP)Ir(CO)(H)(Cl) shown with 50% thermal ellipsoids. Hydrogen atoms, except for the iridium-bound hydride, are omitted for clarity .......................................................................................................20 1 Figure 2.05. H NMR spectrum (300 MHz, acetone-d6) of (iPr)4(POCOP)Ir(CO) showing the resonance for four chemically equivalent methane protons ...........................................................................................................21