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Developing a supramolecular catalyst for asymmetric hydroboration
The design and synthesis of supramolecular catalysts can be classified into two approaches, bottom-up and top-down. The bottom-up approach begins with an enzyme like ‘cage’ or host, and then seeks to incorporate the functionality needed to effect a chemical reaction. An alternative top-down approach begins with a known catalytic reaction, and then seeks to build the requisite supramolecular structure around that functionality to control selectivity. We introduced the chirality-directed self-assembly of bifunctional subunits around a structural metal to form a self-assembled ligand (SAL) in which a second set of ligating groups was suitably disposed to complex a second, catalytic metal center. The major advantage of our SAL system is its ability to create numerous ligands with distinct scaffolds within short period of time. For this thesis studies, we have created over 500 structurally distinctive catalysts and amount of data collected was over 8000. These thesis studies explore the use of SALs for catalytic asymmetric hydroboration, testing the capacity of these SALs to optimize catalysts for electronically and/or sterically differentiated styrenes. Analyzing these results, along with the results obtained from the catalyzed reactions of a series of ortho-, meta- and para-substituted styrenes, suggest that SAL-derived supramolecular catalysts possess a chiral pocket into which substrates must fit. These studies uncovered chiral supramolecular catalysts that afford high levels of enantioselectivity, some the highest enantioselectivities yet reported, and reveal some problems often overlooked using more traditional approaches to catalyst optimization. ^
Moteki, Shin, "Developing a supramolecular catalyst for asymmetric hydroboration" (2008). ETD collection for University of Nebraska - Lincoln. AAI3328256.