Design and Development of Novel Bis(amidophenyl)amine Redox-active Ligands to Promote Novel Reactivity at First-row Transition Metal Centers Open Access

Villanueva, Omar (2015)

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To address the Nation's environmental and energy challenges, chemical catalysis research has shifted its focus to discover new methodologies that can produce alternative fuels and reduce the use of harmful pollutants. At the center of this grand challenge lies the need to discover sustainable transition metal catalysts that utilize environmentally benign reagents for the activation of strong bonds. Developing such systems will bring upon significant technological advances. In Chapter 1, the significance of using earthabundant first-row transition metal ions in catalysis is highlighted and the role of redoxactive ligands in promoting this reactivity is discussed. In chapter 2, the development of coordinatively versatile bis(amidophenyl)amine redox-active ligands as novel motifs to control catalyst structure and reactivity is described. Chapter 3 discloses fundamental spectroscopic, mechanistic, and structural investigations on the reactivity of cobalt(II) complexes of bis(amidophenyl)amine ligands with dioxygen to carry out aerobic oxidation reactions. Given the multi-electron reactivity observed with dioxygen, cobalt(II) complexes were investigated as catalysts for C-H amination catalysis. This dissertation concludes with chapter 4, which deliberates the selective catalytic C-Hamination of aryl azides facilitated by a robust and versatile cobalt(II) catalyst to form medicinally relevant heterocycles. The results presented herein constitute a significant advance in sustainable catalysis technology.

Table of Contents

Chapter 1 Introduction to Redox-active Ligands and Their Role in Promoting Novel Reactivity at First-row Transition Metal Centers. 1

Section 1-1 Introduction. 1

Section 1-2 A Historical Perspective on Redox-active Ligands and Their Metal Complexes. 3

Section 1-3 Redox-active Ligands in Biology. 12

Section 1-4 Utility of Redox-active Ligands in Catalysis. 16

Section 1-4 Dissertation Overview. 20

Chapter 2 First-row Transition Metal Complexes of Coordinatively Versatile Bis(amidophenyl)amine Ligands. 30

Section 2-1 Introduction. 30

Section 2-2 Background and Significance. 41

Section 2-3 Results. 44

Section 2-3-1 Synthesis of Bis(amidophenyl)amine Ligands. 44

Section 2-3-2 Synthesis of Metal Complexes with NH(o-PhNHC(O)R)2 Ligands. 47

Section 2-3-3 X-ray Crystallographic Studies. 54

Section 2-3-4 Electronic and Magnetic Characterization of Metal Complexes. 66

Section 2-3-5 Electrochemical Properties of Metal Complexes. 74

Section 2-4 Discussion. 81

Section 2-5 Conclusion. 85

Section 2-6 Experimental Section. 86

Section 2-6-1 General Considerations. 86

Section 2-6-2 Ligand Syntheses. 87

Section 2-6-3 Complex Syntheses. 91

Section 2-6-4 X-ray Cyrstallographic Data of Complexes. 102

Chapter 3 Mechanistic, Spectroscopic, and Structural Investigations on the Activation of Dioxygen by Cobalt Complexes Incorporating Redox-active Ligands. 113

Section 3-1 Introduction. 113

Section 3-2 Background and Significance. 117

Section 3-3 Results. 122

Section 3-3-1 Stoichiometric Oxygenation and Oxygen-atom Transfer Reaction Studies. 125

Section 3-3-2 Spectroscopic Studies on the Activation of Dioxygen by Cobalt Complexes. 128

Section 3-3-3 Chemical Oxidation of Mononuclear Complex (Et4N)2[Co(HLiPr)2]. 133

Section 3-3-4 Synthetic Studies to Probe Possible Catalyst Structure. 136

Section 3-3-5 Synthetic Studies to Probe the Role of The Ligand Backbone. 147

Section 3-3-6 Synthetic Studies to Establish the Redox Non-innocence of Tridentate, Trianionic Liga nd [LiPr]3-. 151

Section 3-3-7 Synthetic and Spectroscopic Studies Using Zinc(II) To Probe Possible Decomposition Pathway of Bidentate, Dianionic Ligand [LMod]2-. 158

Section 3-3-8 Expanding The Aerobic Oxidation Reactivity Profile of Dinuclear Cobalt(II) Complex, (Et4N)2[Co2(LiPr)2]. 165

Section 3-4 Discussion. 169

Section 3-5 Conclusion. 175

Section 3-6 Experimental Section. 176

Section 3-6-1 General Considerations and Materials. 177

Section 3-6-2 Ligand Syntheses. 178

Section 3-6-3 Complex Syntheses. 182

Section 3-6-4 Reactivity Studies. 189

Section 3-6-5 Crystallographic Data. 199

Chapter 4 Intramolecular sp3 C-H Amination of Aryl Azides Catalyzed by a Cobalt(II) Complex. 209

Section 4-1 Introduction. 209

Section 4-2 Background and Significance. 224

Section 4-3 Results. 228

Section 4-3-1 Initial Investigations on the C-H Amination of an Aryl Azide by Dinuclear Cobalt(II) Complex (Et4N)2[Co2(LiPr)2]. 229

Section 4-3-2 C-H Amination of An Aryl Azide Using Dinuclear Cobalt(II) Complexes With Varying Acyl Substituents. 231

Section 4-3-3 Optimization of Cobalt(II)-Catalyzed C-H amination Reaction. 233

Section 4-3-4 Substrate Scope and Limitations. 235

Section 4-3-5 Kinetic Isotope Effect Study. 240

Section 4-4 Discussion. 241

Section 4-5 Conclusion. 249

Section 4-6 Experimental Section. 250

Section 4-6-1 General Considerations and Materials. 250

Section 4-6-2 General Procedures. 251

Section 4-6-3 Additional Experiments. 259

Section 4-6-4 Crystallographic Data. 262

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