Synthesis, Structure, and Bonding of Macrocyclic Tetra-NHC Complexes of Iron and Cobalt

N-heterocyclic carbenes (NHCs) are key ligands that have broad applications in organometallic chemistry. Several of their benefits stem from their ability to stabilize high oxidation states when bound to transition-metals. In the past two decades, NHC complexes have been developed to study oxidative processes such as nitrogen and oxygen transfer chemistry. Macrocyclic tetra-NHCs, where four NHC units form a cyclic structure, are particularly valuable for stabilizing metals due to their chelation effect. Their rigid structure enforces a well-defined coordination environment, making them highly effective in catalysis. While this growing field of macrocyclic tetra-NHC complexes is promising for studies on synthesis, reactivity, structure, and bonding, studies on this class of NHC still lag behind other poly-dentate NHC ligands.

Presented in this dissertation is an investigation of cyclic tetra-NHC complexes that shows: (1) the reactivity of an iron complex with organic azides, (2) synthetic investigation and structural observations of cobalt complexes, and (3) a synthetic approach to developing chiral macrocyclic tetra-NHC ligand precursors. Chapter two focuses on understanding the reactivity of a chiral tetra-NHC iron complex and organic azides, which form multiple district types of complexes. Chapter three highlights the structure and bonding of cobalt tetra-NHC macrocycles with multiple classes of these ligands. Lastly, chapter four explores the synthesis of new chiral tetra-NHC macrocycles.