GENERATION, CHARACTERIZATION, AND C-H BOND ACTIVATION REACTIVITY BY MONONUCLEAR HIGH-VALENT COBALT(IV) AND NICKEL(IV) NON-OXO COMPLEXES

The study of terminal high-valent transition metal-oxo complexes has increased significantly over the years as it is believed that they are key reactive intermediates for a wide range of biological and industrial catalytic processes. These complexes are powerful oxidants for the activation of strong C-H bonds. The chemical and physical properties of these complexes remain elusive. It is therefore desirable to study the properties and function of these complexes through synthetic models. There have been many efforts and reports of synthetic high-valent metal-oxo complexes of early and middle transition metals (up to group 8 on the Periodic Table of Elements), but as we go beyond group 9, the generation of stable high-valent metal oxo complexes for these transition metals is challenging synthetically. This phenomenon is referred to as the “oxo-wall.” There have been many efforts to break this “oxo-wall” and remains intact to this date. The focus of this research is to study a series of mononuclear cobalt and nickel complexes with oxidation states of +2, +3, and +4. These complexes are supported by a di-anionic, tridentate ligand system and were characterized using various spectroscopic methods such as X-ray crystallography, NMR, EPR, UV-Vis, and DFT computational methods. The generated complexes with an oxidation state of +4 can cleave strong sp3 C-H bonds. This work will inspire to generate more reactive high-valent late transition metal-oxo and non-oxo complexes and understand C-H bond activation in high-valent metal chemistry. Chapter 1 provides a background of synthetic chemistry, generation of high-valent metal-oxo complexes, and the “oxo-wall” theory. Chapter 2 describes the work of the early stages and development of this project leading to how we got to the point in our research currently. Chapter 3 examines and describes the generation, characterization, and reactivity studies of a novel Co(IV)-dinitrate complex. As well as providing preliminary data of a more reactive Co(IV) species. Chapter 4 introduces going beyond cobalt and conducting the similar chemistry with nickel resulting in a high-valent Ni(IV)-nitrate complex. Chapter 5 provides an overall summary and future perspective of the project