Developing Transition Metal Catalysts that Incorporate Redox-Active Ligand Frameworks for Sustainable Catalysis Restricted; Files Only

Abstract

Transition metal catalysis has been an essential pillar of modern organic synthesis. Traditionally, the primary focus has been on using expensive noble metal catalysts since they tend to undergo multi-electron transformations. Recently, the more sustainable first-row transition metal catalysts attracted wide attention with the development of redox-active ligands that can function as electron reservoirs to facilitate multi-electron reactions.

We aim to develop sustainable catalysts that incorporate redox-active ligands with first-row transition metals and use dioxygen as the green oxidant for environmentally benign chemical transformations. In Chapter 2, the design, syntheses, and characterizations of two novel redox-active ligands will be described. These ligands contain a multi-dentate nitrogenous moiety and catechol moieties, allowing more coordinative versatility and electronic tunability of corresponding metal complexes. The catalytic properties of the two resulting Cu complexes, a cobalt cluster, and an iron cluster were investigated by X-ray crystallography, cyclic voltammetry, and UV-vis spectroscopy. Chapter 3 discusses the design, syntheses, and characterizations of terminal alkyne modified redox-active ligands for application in flow chemistry. Cobalt complexes with these newly synthesized ligands were obtained and used in cyclic voltammetry studies, UV-vis spectroscopy, O-atom transfer reaction, and aerobic hydrazone oxidation.

Table of Contents

1. Chapter 1: History and Introduction of Redox-Active Ligands and Their Role in Facilitating Chemical Reactions with First-Row Transition Metals. 1

Introduction. 1

Redox-active ligands in nature. 2

Development of redox-active ligands. 5

Dithiolene ligands. 6

Catecholate ligands—the oxygen analogs. 8

Diimine and amidophenolate ligands—the nitrogen analogs. 10

Iminopyridine ligands. 13

Other imine based ligands. 14

Phenol-containing ligands. 16

Applications of redox-active ligands in catalysis. 18

Carbon–Carbon bond formation. 18

Carbon–Heteroatom bond formation. 21

Aerobic oxidation. 24

Dissertation overview. 26

References. 31

2. Chapter 2: Design and Syntheses of Novel Catecholamine Redox-Active Ligands and the Subsequent Metalations. 45

Abstract 45

Introduction. 47

Results and discussions. 52

Syntheses of the designed redox-active ligands through pathway I 52

Syntheses of the designed redox-active ligands through pathway II 58

Syntheses of metal complexes. 62

Oxidation of K2[Cu(H2L^CAT)2] by dioxygen. 71

Conclusions and future directions. 74

Experimental section. 75

General considerations. 75

Ligand syntheses. 76

References. 83

3. Chapter 3: The Design, Syntheses and Metalation of Alkyne Modified Redox-Active Ligands for Applications in Flow Chemistry. 86

Abstract 86

Introduction. 88

Ligand syntheses. 92

Design of redox-active ligands functionalized with a terminal alkyne. 92

Ligand syntheses in approach A: Terminal alkyne on the aromatic ring. 92

Ligand syntheses in approach B: Terminal alkyne as the amide substituent 98

Syntheses of cobalt complexes. 105

Results and discussions. 106

Aerobic oxidation. 111

Catalytic O-atom transfer reaction. 114

Aerobic catalytic hydrazone oxidation reaction. 115

Conclusions and future directions. 117

Experimental section. 118

General considerations. 118

Ligand Syntheses. 119

Catalytic O-atom transfer reaction procedure. 128

Catalytic hydrazone oxidation reaction procedure. 128

References 129

About this Dissertation

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School	Laney Graduate School
Department	Chemistry
Degree	Ph.D.
Submission	Dissertation
Language	English
Research Field	Chemistry, Organic Chemistry, Inorganic
Keyword	hydrazone oxidation first-row transition metal catalysis aerobic oxidation redox-active ligands
Committee Chair / Thesis Advisor	Cora E. MacBeth, Emory University
Committee Members	Vincent Conticello, Emory University Craig L. Hill, Emory University

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