500 MHz Solid State NMR Spectrometer

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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.