Mechanistic insights into formation and oxidation catalysis of/by FeIV=O and FeV=O: effects of spin state, redox active quinol or oxygen-rich ligands

自然界利用非常活跃的高价铁氧物种(Fe(IV)=O或Fe(V)=O)与氧化还原活性配体和第二球环境相结合来执行极其高效的氧化反应。在这一生物学方法的启发下，本项目将合成一系列含有苯酚或对苯二酚氧化还原非无害单元的单或二聚Fe(II)/Fe(III)配合物。利用我们从以前的研究中得出的机理上的理解，以及在应用相当非传统的低温和高压技术方面的强大专业知识，我们将利用合成的铁络合物来澄清该领域中仍然悬而未决的问题或二分法。将特别关注中自旋(IS)和高自旋(HS)Fe(IV)=O物种的底物氧化机理，以及与IS和HS Fe(IV)=O中间体相比，影响Fe(V)=O物种生成和反应的因素。为此目的合成的铁络合物也代表了合适的体系来研究氧化还原非无辜的喹酚部分的可能参与和/或a(L·)Fe(IV)=O/(L-)Fe(V)=O价互变异构体在Fe(IV)=O的反应中的潜在参与。此外，它们还允许我们探索引入氧供体原子来提供围绕Fe中心的弱配位场对所得到的高价中间体的自旋态和反应活性的影响。为了阐明反应机理和调节反应速率，我们将首次在这一特定的研究领域引入压力效应研究，并将其与通过冷冻-MS研究捕获和检测反应中间体相结合。应该强调的是，本项目预期目标的实现只能通过与参与本研究小组的其他研究小组的合作才能实现，这些研究小组将与我们分享他们在各种光谱和/或理论方法方面的丰富专业知识。反之亦然，我们与机械性调查和相当罕见的方法的应用有关的知识将被提供给我们在这个研究单位内的研究合作者。本项目中预期的各种物理化学方法的合成和应用之间的协同作用不仅将促进我们对活性铁中心发生的事情的了解，而且可以直接为重新设计具有更理想催化特性的新一代功能化铁配合物提供有价值的反馈。

Nature utilizes extraordinarily reactive high-valent iron oxo species (Fe(IV)=O or Fe(V)=O) in combination with redox-active ligands and second-sphere environment to perform extremely efficient oxygenation reactions. Inspired by this biological approach, in this project we will synthesize a series of mono- or dimeric Fe(II)/Fe(III) complexes containing phenol or quinol redox non-innocent units. Taking advantage of our mechanistic understanding, drawn from our previous research, together with a strong expertise in the application of rather unconventional cryo- and high-pressure-techniques, we will employ the synthesized iron complexes to clarify still-open questions or dichotomies existing in the field. Special attention will be paid to the mechanisms of substrate oxidation by intermediate-spin (IS) and high-spin (HS) Fe(IV)=O species and to the factors affecting the generation and reactivity of Fe(V)=O species in comparison to those of IS and HS Fe(IV)=O intermediates. The iron complexes synthesized for this purpose also represent suitable systems to investigate possible participation of redox non-innocent quinol moieties and/or potential involvement of a (L•)Fe(IV)=O/(L- )Fe(V)=O valence tautomerism in the reactivity of Fe(IV)=O. In addition, they will allow us to explore effects of introducing oxygen donor atoms that provide a weak ligand field around the Fe center, on the spin state and reactivity of the resulting high-valent intermediates. With the aim of mechanistic elucidations and modulation of reaction rates, we will introduce, for the first time in this particular research area, pressure effect studies and combine them with trapping and detecting reaction intermediates by cryo-MS investigations. It should be highlighted that the accomplishment of the objectives intended in this project is only achievable within the collaborative work with other research groups involved in this Research Unit that will share with us their strong expertise in various spectroscopic and/or theoretical methods. Vice versa, our knowledge related to mechanistic investigations and application of rather rare methodologies will be offered to our research collaborators within this Research Unit. A synergic interaction between syntheses and application of a variety of physicochemical methodologies anticipated in the present project will not only advance our understanding of what happens at the active iron center, but can directly provide valuable feedback for the redesign of new generations of functionalized iron complexes displaying more desirable catalytic features.