Preventing and Understanding Autooxidation and Side Reactions and Providing a Second Coordination Sphere: Immobilized High Valent Iron Complexes for CH Activation Studies

点击翻译按钮获取中文摘要

Mechanistic studies and a deep understanding of both immobilized and free FeIV=O and FeIII-OH complexes towards C-H bond activation to further the development of oxidation catalysts that can be used in a variety of transformations, is one of the main objectives of this project. Different solid supports will be evaluated for their capability to minimize autoxidation and to enhance reactivity and turnover. Together with direct ligand modifications these immobilized homogeneous catalysts will provide straightforward access to electronic and steric tunability. In addition, substrate scope will be extended for the biomimetics to move toward real applications and to unravel unusual α-KG/iron dependent enzyme mechanisms. Specifically, we want to answer the following questions together with the experts in this FOR: What is the importance of the comproportionation of the FeIV and FeII species for the general outcome of an oxidative transformation? Here, we will use stopped-flow and ESI-MS techniques as well as Mössbauer spectroscopy which will give insight into the Fe-species at different time points in solution. Furthermore, theoretical computation of the involved structures, transition states, and intermediates will further our understanding of these reactions. Secondly, we will study how relevant the FeIII-OH species are for biomimetic substrate oxidations and how model studies can shed light on the mechanisms of HMS, HPDL and HPPD enzymes. We will thus study the reactivity of both FeIII-hydroxido and the FeIV-oxo species towards a range of biologically relevant substrates. Thirdly, we will investigate how different solid supports mimic a second coordination sphere and whether these alter the reactivity compared to the homogeneous model complex reactions. Comparison of the activity and substrate scope of immobilized compared to free complexes will guide us in the understanding of the importance of a second coordination sphere. The vision of this project is to not only enhance our understanding of the reactivities of different iron species but to develop targeted complexes, that exhibit less side reactions, are more specific and can be tuned towards a certain outcome. Specifically, the goal of this project is to target either biologically, synthetically or industrially relevant oxidative transformations. This can only be achieved if the catalysts are fully understood and their tuneability has been demonstrated.