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Synthesis of Functionalized Benzenoid Macrocycles: an Approach to Accessing Functionalized Cycloparaphenylenes

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Synthesis of Functionalized Benzenoid Macrocycles: an Approach to Accessing Functionalized Cycloparaphenylenes Synthesis of Functionalized Benzenoid Macrocycles: An Approach to Accessing Functionalized Cycloparaphenylenes by Rolande Meudom A thesis submitted to the Graduate Faculty of Auburn University in partial fulfillment of the requirements for the Degree of Master of Science Auburn, Alabama May 8, 2016 Keywords: Carbon nanotubes, Cycloparaphenylenes, p-terphenylophanes, Bent p-phenylene Macrocycles, Copyright 2016 by Rolande Meudom Approved by Bradley L. Merner, Chair, Assistant Professor of Chemistry and Biochemistry Peter Livant, Associate Professor of Chemistry and Biochemistry Anne E. V. Gorden, Associate Professor of Chemistry and Biochemistry Steven Mansoorabadi, Assistant Professor of Chemistry and Biochemistry Abstract Carbon nanotubes (CNTs) are cylindrically shaped allotropes of carbon with exceptionally good electronic and optical properties. The current state of art for making these CNTs involves heating graphite in a high temperature furnace (above 600 °C). The use of harsh temperatures makes the process unselective and produces CNTs as an inseparable mixture of products. Currently, there is no efficient purification technique for isolating pure CNTs. In order to fully exploit the electronic properties of CNTs, they need to be made as homogeneous and monodispersed structures. Thus, synthetic chemists envisioned using chemical synthesis from the ground-up via a template strategy as a more viable approach to achieve the selective synthesis of uniform CNTs structures with a defined chirality and diameter. This is because the selective synthesis of curved PAHs like [n]ciruclenes and CNT substructures could only be accomplished through chemical synthesis. The work described herein focuses on a new approach to accessing highly distorted p-phenylenes, which does not rely on cross coupling reactions and the use of the Burgess reagent as a mild dehydrative aromatization agent, giving access to highly strained benzenoid macrocycles. Chapter 1: A definition of CNTs, types of CNTs and their properties. A description of the industrial processes used in the synthesis of CNTs and their limitations. The selective synthesis of some curved PAHs like [n]circulenes and CNT substructures is described to illustrate the power of chemical synthesis in achieving challenging targets. ii Chapter 2: A template approach to the synthesis of uniform, single chirality CNT is described. Various approaches to CPP synthesis have equally been covered as well as the current limitation in the field. A non-cross-coupling approach to bent paraphenylenes have been described, as well as arene bridging strategy tolerable to ortho substitutents. Moreover, the use of the Burgess reagent as a powerful dehydrative aromatizing agent to achieve highly distorted paraphenylene and prevent rearrangements is demonstrated. Furthermore, a streamlined approach to access gram quantities of macrocyclic 1,4-diketones from acyclic dialdehydes has been developed which uses mild hydrogenation source, which has provided access to a wide variety of targets not accessible by other methods. Chapter 3: The synthesis of functionalized benzenoid macrocycles with ortho substituents is undertaken and progress towards converting them into functionalized CPPs is reported. iii Acknowledgments My sincere gratitude goes to my advisor Dr. Bradley L. Merner for his incredible advice and guidance throughout my graduate studies. I also wish to thank him for his patience towards me. I have learned a lot from his laboratory and his person and I believe this training will be of valuable help in my future endeavors. I equally wish to thank my committee members, Dr. Gorden, Dr. Livant and Dr. Mansoorabadi for serving as my advisory committee. I would also like to express gratitude to my lab mates, especially Nirmal Mitra with whom I worked closely on this project. My regards also go to Dr. John Gorden for his expertise in obtaining X-ray crystal structures for my compounds and Dr. Michael Meadows for his assistance in using the NMR facilities. I am equally thankful to my friends and family members, especially my brother Fopessi Camille and my sister Titane Isabelle Massop, for their love, help, support, and encouragements despite the distance that separate us. Last but not the least, I’m grateful to God almighty for his strength and love throughout my life. iv Table of Contents Abstract ........................................................................................................................................... ii Acknowledgments.......................................................................................................................... iv List of Tables ............................................................................................................................... viii List of Schemes .............................................................................................................................. ix List of Figures ............................................................................................................................... xii List of Abbreviations ................................................................................................................... xiv Chapter 1 : Chemical Synthesis of Carbon Nanotubes (CNTs) and Related Substructures ........... 1 1.1 Definition of CNTs and Applications .................................................................................... 1 1.2 Types of CNTs ...................................................................................................................... 2 1.3 Traditional (Industrial) Methods for Making Carbon Nanotubes ......................................... 2 1.3.1 Physical Processes .......................................................................................................... 2 1.3.2 Chemical Processes ........................................................................................................ 5 1.4 Limitations of Traditional (industrial) Methods for Making CNTs ...................................... 7 1.5 Synthesis of CNT Substructures ........................................................................................... 8 1.5.1 Synthesis of [n]Circulenes .............................................................................................. 8 1.5.2 Synthesis of Buckminsterfullerene (C60) ...................................................................... 12 1.5.3 Synthesis of the End Cap of [5,5]Armchair CNT ........................................................ 13 1.5.4 Synthesis of Warped Nanographene ............................................................................. 16 1.5.5 Synthesis of Nonplanar Pyrenoid Systems ................................................................... 18 v Chapter 2 : Benzenoid Macrocycles: Templates for the Bottom-up Synthesis of CNTs ............. 23 2.1 Bottom-up Synthesis of Armchair CNTs ............................................................................ 23 2.2 Synthetic Approaches to [n]Cycloparaphenylenes (CPPs) ................................................. 24 2.2.1 Early Attempted Synthesis of [n]CPPs ......................................................................... 24 2.2.2 A Generalized Approach to [n]CPPs ............................................................................ 30 2.2.3 Different Approaches to CPP Synthesis ....................................................................... 31 2.3 Major Limitations in [n]CPP Synthesis .............................................................................. 35 2.3.1 Direct Regioselective (Late-Stage) Functionalization .................................................. 35 2.4 Functionalized CPPs as Better Templates for Armchair CNT Synthesis ........................... 38 2.5 Insight into the Present Research and Generation of Hypothesis ....................................... 41 2.5.1 Project Goal and Plan ................................................................................................... 41 2.6 A Non-Cross Coupling Approach to Arene-Bridged Macrocycles: Regioselective Functionalization of CPP Substructures, and the Synthesis of Congested Benzenoid Macrocycles ........................................................................................................................ 45 2.6.1 A Non-Cross Coupling Approach to Strained Biaryl Macrocycles ............................. 45 2.6.2 Synthesis of 1,7-dioxa[7](3,3″)-p-terphenylophane ([7]PTPP).................................... 47 2.7 Streamlined Synthesis of Macrocyclic 1,4-diketone ........................................................... 50 2.8 Optimization of Grignard Reaction (Solvent/Size-Dependent Diastereoselectivity) ......... 53 2.9 Synthesis of 1,6-dioxa[6](3,3″)-p-terphenylophane ([6]PTPP)-A More Strained System . 58 2.10 Synthesis of p-cyclo[8]-p-Terphenylophane ..................................................................... 64 2.11 Late Stage/Regioselective Bromination of [7]PTPP ......................................................... 65 Chapter 3 : Towards the Synthesis of Functionalized [n]CPPs .................................................... 68 vi 3.1 Synthesis of Functionalized [n](3,3")p-terphenylophanes: Precursors to Functionalized Cycloparaphenylenes (CPPs) ............................................................................................. 68 3.1.1 Early-Stage Suzuki Reaction: Challenging Grignard ................................................... 68 3.1.2
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