500 MHz Solid State NMR Spectrometer

表征固定在表面上的有机金属和有机催化剂是极具挑战性的，部分原因是催化剂固定在表面的复杂性，部分原因是测量技术的复杂性，这通常需要比基于溶液的样品更先进的设备。固体核磁共振是表征固体表面固定化催化剂的最重要的技术之一，因为它可以让我们确定单个活性位点的化学状态，与模型配合物的溶液相数据相比，还可以获得传统液态核磁共振无法获得的固体表面上物质结构和构象的更多信息。特别是，固态核磁共振光谱使我们能够利用分子间的偶极耦合，而在液态核磁共振中，这是通过分子翻滚来平均的。这种偶极耦合既可以通过相关光谱（如HETCOR、自旋扩散和TRAPDOR实验）进行定性测量，也可以通过REDOR、SEDOR和POSTC7光谱等方法进行定量测量（以获得原子间距离）。在斯图加特大学的CRC 1333中，24名主要研究人员正在就19个研究课题进行合作，这些课题涉及将固定化有机金属和有机催化剂限制在介孔支架内的影响。限制在受限的几何结构中会影响催化反应的活性和选择性，迫使活性位点形成新的、更活跃的/选择性的构象，而这些构象在中孔环境之外是无法获得的。为了充分了解这些效应，活性位点的高质量固态核磁共振表征是必不可少的。利用二维（和一维）相关光谱来了解孔隙中活性位点的二级结构是必要的。具体来说，我们建议使用相关方法来理解a)构象几何形状的变化，b)活性位点与孔壁的关联，以及c)附近活性位点之间的密切关联。这样的测量是不可能的，以我们目前在斯图加特大学的核磁共振能力。在这个项目中，我们提出了一个新的四通道500 MHz固态核磁共振波谱仪优化二维相关光谱。有了这个光谱仪，将有可能了解在孔内形成的二级结构，并影响我们的限制性异质活性位点的催化活性和选择性。如果没有这样的光谱仪，我们将永远无法完全理解为什么限制会影响CRC 1333中研究的催化反应。

Characterization of organometallic and organocatalysts immobilized on surfaces is extremely challenging, owing in part to the complexity of the surfaces on which the catalysts are immobilized and in part to complications in the measurement techniques, which often require more advanced equipment than for solution-based samples. Solid-state NMR is one of the most important techniques for characterizing immobilized catalysts on solid surfaces, because it allows us to determine the chemical state of individual active sites, compared to the solution phase data of the model complexes, and also obtain more information about the structures and conformations of species on solid surfaces not available by traditional liquid state NMR. In particular, solid state NMR spectroscopy allows us to take advantage of intermolecular dipolar coupling, which in liquid state NMR is averaged out by molecular tumbling. Such dipolar coupling can be measured both qualitatively by correlation spectroscopies such as HETCOR, spin diffusion, and TRAPDOR experiments and quantitatively (to get interatomic distances) via methods such as REDOR, SEDOR, and POSTC7 spectroscopies. In the CRC 1333 at the University of Stuttgart, 24 principal investigators are collaborating on 19 research topics concerning the effects of confining immobilized organometallic and organocatalysts inside mesoporous supports. Confinement in the constrained geometries affects both the activity and selectivity of the catalytic reactions by forcing the active sites into new and more active/selective conformations not accessible outside of the mesopore environment. In order to fully understand these effects, high-quality solid-state NMR characterization of the active sites is essential. It is necessary to use 2D (and 1D) correlation spectroscopies to understand the secondary structures of the active sites in the pores. Specifically, we propose to use correlation methods to understand a) changes in conformational geometry, b) association of active sites with the pore wall, and c) close association of nearby active sites with each other. Such measurements are not possible with our current NMR capabilities at the University of Stuttgart. In this project, we propose the acquisition of a new four channel 500 MHz solid-state NMR spectrometer optimized for 2D correlation spectroscopies. With this spectrometer it will be possible to understand the secondary structures that form inside the pores and affect the catalytic activity and selectivity of our confined heterogenized active sites. Without such a spectrometer, we will never be fully able to understand why confinement affects the catalytic reactions studied in the CRC 1333.