Advanced X-ray Spectroscopic Approachesfor the Characterization ofHigh-Valent Iron Intermediates

这项建议将侧重于先进的X射线光谱方法的开发和应用，以了解生物启发的均相催化剂介导氧化反应的机理。我们将开发1s2p共振非弹性X射线散射(RIXS)、1s3p RIXS、1s价RIXS和2p3d RIXS的完整信息量，以及这些方法与高价铁中间体的相关性。RIXS实验是有效的二维光谱测量，它将选定的XAS边缘与选定的X射线发射能量范围相结合，以选择特定的基态、中间态和终态组合。因此，这些实验实现了更高选择性的高分辨率X射线吸收光谱XAS(来自1s2p RIXS)、自旋和氧化态选择性XAS(1s3p RIXS)、配体和偏振选择性(1s价态RIXS)以及进入低激发态d-d(2p3d RIXS)。其中许多实验仍处于早期开发阶段，因此对表征良好的Fe(IV)-氧代、Fe(III)-过氧基和Fe(II)前体络合物进行一系列平行实验将是重要的。这些光谱的信息量将通过与理论的密切关联来确定。实验和理论的关联将使我们能够建立正确的方法组合，最大限度地洞察电子结构的变化，并最终了解催化剂的作用机理。我们最初的研究将集中在静态冷冻(或冷冻淬火)样品上，然后将扩展到利用微流控混合器的现场研究，我们目前正在开发这种混合器。在合作研究团队内开发的催化剂的静态和现场/操纵面光谱研究将提供对O-O键断裂、O-原子转移和C-H原子抽象过程的关键洞察。这些发现将为未来基于知识的催化设计奠定基础。

This proposal will focus on the development and application of advanced X-ray spectroscopic methods to understand the mechanisms of bioinspired homogenous catalysts which mediate oxygenation reactions. We will develop the full information content of 1s2p resonant inelastic X-ray scattering (RIXS), 1s3p RIXS, 1sValence RIXS and 2p3d RIXS, and the relevance of these methods to high valent iron intermediates. RIXS experiments are effectively two-dimensional spectroscopic measurements that combine a selected XAS edge with a selected X-ray emission energy range to select for a specific combination of ground, intermediate and final states. As such, these experiments enable greater selective enabling higher resolution X-ray absorption spectroscopy XAS (from the 1s2p RIXS), spin and oxidation state selective XAS (1s3p RIXS), ligand and polarization selectivity (1sValence RIXS) and access to low lying d-d excited states (2p3d RIXS). Many of these experiments are still in an early development phase, and hence it will be important to perform a range of parallel experiments on well-characterized Fe(IV)-oxo, Fe(III)-peroxo, and Fe(II) precursor complexes. The information content of these spectra will be established through close correlation to theory. The correlation of experiment and theory will allow us to establish the right combination of methods to maximize insight into the electronic structural changes and ultimately to the mechanism of operating catalysts. Our initial studies will focus on static frozen (or freeze-quenched) samples and will then be extended to in situ studies utilizing microfluidic mixers, which we are currently developing. Static and in-situ/operando spectroscopic studies of catalysts developed within the collaborative research team will provide key insight into the processes of O-O bond cleavage, O-atom transfer and C-H atom abstraction. These findings will form a basis for future knowledge based catalytic design.