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

研究和深入了解固定和游离FeIV=O和feii - oh配合物对C-H键活化的机理，以进一步开发可用于各种转化的氧化催化剂，是该项目的主要目标之一。不同的固体载体将评估其能力，以减少自氧化和提高反应性和周转。与直接配体修饰一起，这些固定化均相催化剂将提供直接的电子和空间可调性。此外，将扩大底物范围，使仿生学走向实际应用，并揭示不寻常的α-KG/铁依赖酶机制。具体来说，我们想和这个FOR的专家一起回答以下问题：FeIV和FeII物种的比例对氧化转化的一般结果有什么重要性？在这里，我们将使用停流和ESI-MS技术以及Mössbauer光谱，这将深入了解溶液中不同时间点的铁种。此外，理论计算所涉及的结构，过渡态和中间体将进一步加深我们对这些反应的理解。其次，我们将研究feii - oh与仿生底物氧化的相关性，以及模型研究如何揭示HMS， HPDL和HPPD酶的机制。因此，我们将研究feii -羟基和feiv -氧对一系列生物学相关底物的反应性。第三，我们将研究不同的固体载体如何模拟第二配位球，以及与均相模型复杂反应相比，这些载体是否会改变反应活性。与游离配合物相比，固定化配合物的活性和底物范围的比较将指导我们理解第二配位域的重要性。该项目的愿景不仅是提高我们对不同铁物种的反应性的理解，而且是开发有针对性的配合物，表现出更少的副反应，更具体，可以调整到一定的结果。具体来说，这个项目的目标是针对生物、合成或工业相关的氧化转化。这只有在催化剂被充分理解和它们的可调性被证明的情况下才能实现。

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.