Atom and Group Transfer Reactions Involving High-valent Iron Complexes

Abstract: Iron enzymes play critical roles in biological oxidation reactions by utilizing highly reactive high-valent iron intermediates, such as FeIV=O, FeV(O)(OH), and FeIV=NR species, for catalytic reactions. These intermediates exhibit remarkable catalytic behavior with high reactivities and high regio- and stereospecificity in various biochemical reactions. Understanding these metal intermediates is crucial not only for replicating their activity but also for discovering new synthetic possibilities in chemical synthesis.To address the challenge of comprehending high-valent iron intermediates in biology, chemists have developed a number of bio-inspired functional models that exhibit a diverse range of catalytic properties. The main objective of this thesis is to examine the functional mimicry of mononuclear non-heme active sites in iron enzymes, specifically targeting FeIV=O, FeV(O)(OH) and FeIV=NR intermediates. Chapter 1 provides an introduction to active sites of iron enzymes in biological systems and related bio-inspired models utilizing iron complexes. Chapter 2 relates to Papers I and IV. Paper I describes the syntheses and characterizations of four new FeIV=O complexes based on new ligands with minor steric restriction. The reactivity of these complexes in C-H activation and O-atom transfer reactions has been investigated in detail. As the ligands include negligible steric restrictions, the reactivity differences between these FeIV=O complexes are attributed to the electronic properties of the ligands. On the other hand, Paper IV provides an example of a ligand framework where the steric restrictions of the specific ligand dictate the substrate accessibility. Chapter 3 relates to Paper II and gives a comparative study on the structure and reactivity patterns of a new FeIV=NR complex versus its FeIV=O congener. Chapter 4 relates to Paper III and studies the epoxidation of alkenes by two mononuclear non-heme FeIV=O complexes based on ligands with different electron-donating properties. The catalysis and kinetics studies shed light on the influence of electron-donating properties on the reactivity and mechanism of alkene epoxidation.This research provides insights into the influence exerted by ligand environments on the reactivities of FeIV=O, FeV(O)(OH) and FeIV=NR complexes. The study may contribute to the development of new, highly active catalysts for important oxidation reactions.