Synthesis and DNP enhanced Solid-State-NMR Characterization of immobilized enantioselective Catalysts.

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The objective of the present proposal is the development of novel enantioselective mono- or binuclear supported homogeneous metal-organic catalysts, the evaluation of their catalytic performance, stability and reactivity, and their detailed characterization by multinuclear 1D and 2D solid-state NMR and Dynamic Nuclear Polarization (DNP) enhanced surface solid-state NMR spectroscopy. As carrier materials for the immobilization, biocompatible materials based on nanocrystalline cellulose (CNC) are employed. The functionalized CNCs will be used as carrier material for the immobilization of chiral homogeneous mono- and binuclear rhodium catalysts, which are employed in the synthesis of pharmaceutical compounds such as milnacipran, a clinically efficient antidepressant and the enantioselective hydrogenation step in the synthesis of L-DOPA, a therapeutic agent for Parkinsons disease. Different synthetic routes for the grafting of chiral rhodium or dirhodium complexes (i.e. tethering, ligand exchange or axial coordination) are investigated. The resulting catalysts will be first evaluated in enantioselective cyclopropanation or hydrogenation reactions on model compounds in different organic solvents and aqueous media. Signal enhancement by DNP is achieved by impregnation with radical solutions or by developing and applying new DNP techniques for matrix/solvent free characterization, which are more amenable to the heterogeneous catalyst characterization in a real chemical environment. For this, we will develop and synthesize new DNP active silica and CNC support materials with covalently bound radicals and evaluate the effect of the tethering on their EPR parameters and DNP activity under different reaction conditions.