The Coordination Chemistry of Hydrogen Peroxide Open Access

Wallen, Christian (2017)

Permanent URL: https://etd.library.emory.edu/concern/etds/pc289j90s?locale=en
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Abstract

Hydrogen peroxide is generally hailed as a green oxidant, since it produces water as the sole stoichiometric byproduct and it has a high oxidative efficiency. It can be safely manufactured on scale and is used in the epoxidation of propylene and in the delignification of wood pulp for paper production. Since hydrogen peroxide has relatively low oxidative power, it usually requires activation by a transition metal catalyst. These catalytic systems typically generate M-OOH, M=O, M-O-M, or hydroxyl radical species, which have limitations in oxidative scope and selectivity. Metal hydrogen peroxide adducts have been kinetically and computationally implicated as active intermediates in oxidative mechanisms but have previously never been observed experimentally. The work herein describes the first observed M(H2O2) adducts with transition metals, explores the thermodynamics of their formation, and investigates their stability to disproportionation. The information gained in this work could ultimately set the stage for the development of novel oxidative methodologies employing hydrogen peroxide as the sole stoichiometric oxidant.

The first part of this work describes the formation of a Zn(H2O2) adduct with a sulfonamido ligand. Computational evidence suggests that hydrogen bonding acceptors stabilizing binding of hydrogen peroxide to metal ions so a ligand was prepared with an open metal coordination site surrounded by sulfonyl groups, which serve as strong hydrogen bond acceptors. This ligand successfully stabilizes binding of H2O2 and the first crystal structure of an M(H2O2) adduct was obtained. In the third chapter, the binding of H2O2 to a redox-active metal (Co) is observed spectroscopically and the first binding constant for H2O2 bound to a metal ion was measured. In the next chapter, the sulfonamido ligand electronics were further explored through the preparation of heterotrimetallic complexes bearing a novel alkyl sulfonamido ligand, which demonstrates increased electron density on the sulfonyl groups. The final chapter further explores the formation of M(H2O2) adducts with redox-active metals (Co, Ni, and Cu) on sulfonamido ligands, establishing the influence of changing counterion, ligand electronics, and metal identity on binding strengths and decay kinetics.

Table of Contents

Table of Contents Chapter 1. Hydrogen Peroxide: Production, Application, and Reactivity with Transition Metals 1

1.1 Industry of Hydrogen Peroxide..................................................................................... 2

1.2 Established Mechanisms for Hydrogen Peroxide Activation......................................... 7

1.3 Theoretical Hydrogen Peroxide Activation Mechanisms............................................. 13

1.4 Theoretical Support For M(H2O2) Adducts................................................................. 16

1.5 References.................................................................................................................... 19

Chapter 2. A Hydrogen Peroxide Complex of Zinc...................................................... 24

2.1 Abstract........................................................................................................................ 25

2.2 Introduction.................................................................................................................. 25

2.3 Results and Discussion................................................................................................ 28

2.4 Conclusions................................................................................................................. 37

2.5 Experimental................................................................................................................ 38

2.6 References.................................................................................................................... 52

Chapter 3. Hydrogen Peroxide Coordination to Cobalt(II) Facilitated by Second-Sphere Hydrogen Bonding 58

3.1 Abstract........................................................................................................................ 59

3.2 Introduction.................................................................................................................. 59

3.3 Results and Discussion................................................................................................ 61

3.4 Conclusions................................................................................................................. 71

3.5 Experimental................................................................................................................ 72

3.6 References.................................................................................................................... 88

Chapter 4. Heterotrimetallic Sandwich Complexes Supported by Sulfonamido Ligands 93

4.1 Abstract........................................................................................................................ 94

4.2 Introduction.................................................................................................................. 94

4.3 Results and Discussion................................................................................................ 97

4.4 Conclusions............................................................................................................... 112

4.5 Experimental.............................................................................................................. 113

4.6 References.................................................................................................................. 126

Chapter 5. Coordination of Hydrogen Peroxide with Late Transition Metal Sulfonamido Complexes 136

5.1 Abstract...................................................................................................................... 137

5.2 Introduction................................................................................................................ 137

5.3 Results and Discussion.............................................................................................. 140

5.4 Conclusions............................................................................................................... 157

5.5 Experimental.............................................................................................................. 158

5.6 References.................................................................................................................. 168

Appendix 1. NMR Characterization Data.................................................................. 171 Appendix 2. Crystallographic Data............................................................................. 180

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