A STUDY OF A REDOX NON-INNOCENT TETRADENTATE DIAMIDE-DIIMINE LIGAND CHELATED TO TITANIUM, CHROMIUM, AND IRON: FROM CATALYTIC NITRENE GROUP TRANSFER TO ELECTRONIC STRUCTURE

Abstract

Redox non-innocent (RNI) or "redox-active" ligands have become an essential part of inorganic chemistry. RNI dithiolate ligands studied in the 1960’s contributed to our understanding of electronic structure and utilized the recently developed ligand field theory. Since then, RNI ligands have been discovered in naturally occurring sources such as cytchrome P-450, and have found myriad applications in synthetic transition metal chemistry and catalysis. RNI ligands can be leveraged to tune the electronic structure of transition metal complexes to confer nobility upon first row transition metals or promote desirable one electron processes. While RNI ligands of various forms have been studied for over 50 years, there is still much to be explored. Modern analytical techniques and computational methods have expanded the chemist’s ability to study these systems to gain a deeper understanding of the effects of electronic structure on reactivity. The purpose of this work is to expand the knowledge of RNI ligands and to understand how redox non-innocence manifests reactivity and affects the electronic structure of first row transition metal complexes. To achieve this goal, a detailed synthetic and reactivity study of the tetradentate diamide-diimine (dadi) ligand chelated to titanium, chromium, and iron was pursued. The study began initially with synthesis of the dadi ligand and the titanium, chromium, manganese, and iron complexes, which was performed by Dr. Wesley Morris in this laboratory. Following the early work of Dr. Morris, the reactivity of the chromium and iron dadi complexes was explored. This work found RNI was responsible for the processes observed in the system that ultimately lead to formal insertion of imidyls into the C-C bond of the ligand backbone. Along the same vein, the RNI of the dadi ligand was found to be critical for nitrene group transfer that generated adamantyl isocyanate, catalyzed by a titanium imido species. In between these highlights of chemistry, various metal complexes were synthesized to probe the electronic structure, and to discover new and interesting chemistry. The diversity of reactions available to a single RNI ligand is exemplified in the later chapters of this work. A direct carbene transfer was discovered to be effected by the RNI dadi ligand, providing insight into the mechanism of metal catalyzed cyclopropanations. In the final expansion of this work, radical type reactions were discovered that diverge from the previously studied nitrene transfer, a 2-electron process.