UNIVERSITY OF CALIFORNIA, SAN DIEGO Experimental and Theoretical Investigations into the Stabilization of Captodative (Amino)(Carboxy) Radicals A dissertation submitted in the partial satisfaction of the requirements for the degree of Doctor of Philosophy in Chemistry by Janell Kathryn Mahoney Committee in charge: Professor Guy Bertrand, Chair Professor Adah Almutairi Professor Joshua Figueroa Professor Michael Tauber Professor William Trogler 2017 Copyright Janell Kathryn Mahoney, 2017 All rights reserved. The Dissertation of Janell Kathryn Mahoney is approved, and it is acceptable in quality and form for publication on microfilm and electronically: Chair University of California, San Diego 2017 iii DEDICATION This thesis is dedicated to my family and fiancé. iv TABLE OF CONTENTS Signature Page ........................................................................................................................... iii Dedication ................................................................................................................................... iv Table of Contents ........................................................................................................................ v List of Abbreviations .................................................................................................................. vii List of Figures ........................................................................................................................... viii List of Schemes ......................................................................................................................... xii List of Tables ............................................................................................................................ xiii Acknowledgments .................................................................................................................... xiv Vita...........................................................................................................................................xviii Abstract of the Dissertation ....................................................................................................... xx General Introduction .................................................................................................................... 1 Chapter 1: Bottleable (Amino)(Carboxy) Radicals Derived from Cyclic (Alkly)(Amino) Carbenes ...................................................................................................................................................15 Introduction ...................................................................................................................16 (A) A monomeric (amino)(carboxy) radical .................................................................17 (B) Di- and tri-(amino)(carboxy) radicals ....................................................................20 Conclusion ...................................................................................................................23 Appendix: Experimental Section ..................................................................................24 Chapter 2: Air-Persistent (Amino)(Carboxy) Radicals Derived from Cyclic (Alkyl)(Amino) Carbenes ..................................................................................................................................32 Introduction .................................................................................................................33 (A) Computational analysis .........................................................................................34 v (B) Experimentally obtained (amino)(carboxy) radicals ..............................................37 Conclusion ....................................................................................................................44 Appendix: Experimental Section ..................................................................................45 Chapter 3: The Suitability of Stable Acyclic Carbenes as Building Blocks for Capto-dative C- Centered Radicals ...................................................................................................................71 Introduction ...................................................................................................................72 (A) Cyclic and acyclic N-heterocyclic carbenes ........................................................... 74 (B) Acyclic (amino)(alkyl) carbene ...............................................................................81 (C) Discussion ..............................................................................................................72 Conclusion ....................................................................................................................86 Appendix: Experimental Section ..................................................................................87 Chapter 4: A Redox Bistable Molecular Switch Built from (Amino)(Carboxy) Radical Architecture ...................................................................................................................................................96 Introduction ...................................................................................................................97 (A) A molecular switch ..............................................................................................100 (B) Tuning redox bistability as a function of the carbene ligand ................................ 106 (C) Molecular switches: other models ........................................................................108 Conclusion ..................................................................................................................117 Appendix: Experimental Section ................................................................................ 118 Conclusion ..............................................................................................................................139 References .............................................................................................................................145 vi LIST OF ABBREVIATIONS Bz: Benzoyl Bn: Benzyl CAAC: Cyclic (alkyl)(amino) carbene DDQ: 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone DIPP: 2,6-iPr2(C6H3) DFT: Density functional theory ERP: Electron paramagnetic resonance iPr: Isopropyl LUMO: Lowest unoccupied molecular orbital Me: Methyl MES: 2,4,6-Me3(C6H2) NHC: N-heterocyclic carbene Ph: Phenyl RDE: Rotating disk electrode SOMO: Singly occupied molecular orbital TDAE: Tetrakis(dimethylamino)ethylene THF: Tetrahydrofuran ZORA: Zeroth order regular approximation vii LIST OF FIGURES Figure I.1: Gomberg’s radical. ................................................................................................... 3 Figure I.2: Modified tri(phenyl)methyl radicals. .......................................................................... 4 Figure I.3: Poly-radicals related to the tri(phenyl)methyl radical. .............................................. 5 Figure I.4: Phenalenyl radical and its σ-dimer (left) and the SOMO (right). .............................. 6 Figure I.5: The 2,5,8-tri-tert-butylphenalenyl radical and its π-dimer. ....................................... 6 Figure I.6: Nitrogen containing phenalenyl radicals. ................................................................. 7 Figure I.7: Cyclopentadienyl radicals. ........................................................................................ 8 Figure I.8: The singlet and triplet carbene electronic states ...................................................... 9 Figure I.9: A stable cyclic (alkyl)(amino) carbene (CAAC). ..................................................... 10 Figure I.10: Carbene supported paramagnetic metal complexes. .......................................... 11 Figure I.11: Selected examples of carbene stabilized main group paramagnetic species. .... 12 Figure I.12: Organic radicals derived from carbenes. ............................................................. 13 Figure 1.1: Examples of captodative substituted radicals and carbene derived organic radicals. .................................................................................................................................................. 16 Figure 1.2: Cyclic voltammogram of 1.2a. Potentials referenced with respect to Fc+/Fc. ....... 18 Figure 1.3: X-ray structure of 1.2a and 1.3a. Hydrogen atoms, solvent molecules and the chloride anion (for 1.2a) were omitted for clarity. ..................................................................... 18 Figure 1.4: Left: Representation of the SOMO of 1.3a (isosurfaces at 0.05au). Right: X-band EPR spectra of 1.3a in benzene at room temperature. ............................................................ 19 Figure 1.5: Cyclic voltammogram of 1.2b (top) and 1.2c (bottom). Corrected with respect to the Fc+/Fc. ...................................................................................................................................... 21 Figure 1.6: X-ray crystal structure of 1.2b. Hydrogens, solvent molecules, and chloride anions are omitted for clarity. ............................................................................................................... 21 Figure 1.7: X-ray crystal structures of 1.3b (right) and 1.3c (left). Hydrogen atoms and solvent molecules as well as the isopropyl, ethyl, and methyl substituents of 1.3c, are omitted for clarity.