Surface enhanced NMR spectroscopy (SENS) can be achieved by using dynamic nuclear polarization (DNP). In this approach, electron polarization is transferred from an organic radical to the rare nuclei (at natural isotopic abundance) at the surface, yielding more than a hundred-fold signal enhancement for surface species in silica frameworks.Here we show the full characterisation by DNP SENS of a hybrid organic-inorganic silica material containing homogeneously distributed Pd-NHC complexes that is active for the Z-selective hydrogenation of alkynes. The results confirm the well-defined uniform environment of the Pd-complex on the surface silica material. We then go on to determine secondary interactions that are demonstrated to direct the stability of well-defined Ru-NHC based heterogeneous alkene metathesis catalysts. Specifically, we determine the interactions between the metal center (active site) and the surface functionality of the support. The interactions are present only when the metal center is attached at the surface via a flexible linker (a propyl group), which allows the active site to either react with the substrate or relax � reversibly � to the surface, thus providing stability. In contrast, the use of a rigid linker leads to a well-defined active site far away from the surface, and we show that this leads to faster decomposition and deactivation of the catalysts.

DNP surface enhanced NMR spectrosopy for the characterisation of metal-surface interactions in catalysts

247th National Meeting (2014)

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