NMR Quantification of the Effects of Ligands and Counterions on Lewis Acid Catalysis

The relative Lewis acidity of a variety of metal–ligand catalyst complexes is quantified using 31P NMR spectroscopy. Three 31P NMR probes, including two new bidentate binding probes, are compared on the basis of different binding modes (i.e., monodentate vs bidentate) and the relative scale of their...

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Bibliographic Details
Published in:Journal of organic chemistry 2019-12, Vol.84 (24), p.15845-15853
Main Authors: Jennings, Julia J, Wigman, Benjamin W, Armstrong, Brittany M, Franz, Annaliese K
Format: Article
Language:English
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Summary:The relative Lewis acidity of a variety of metal–ligand catalyst complexes is quantified using 31P NMR spectroscopy. Three 31P NMR probes, including two new bidentate binding probes, are compared on the basis of different binding modes (i.e., monodentate vs bidentate) and the relative scale of their downfield shift upon binding to Lewis acid complexes. Bidentate coordination of catalyst complexes including metal catalysts, ligands, and counterions were assessed due to their importance to asymmetric catalysis. The effect of ligands, counterions, and additives on Lewis acidity is quantified and correlated to reaction yield at an early time point as an approximation for catalytic activity/efficiency and chelation mode in two organic transformations. Binding studies were performed under catalytically relevant conditions, giving further applicability to synthesis. Insight into activation modes are revealed through this analysis.
ISSN:0022-3263
1520-6904
DOI:10.1021/acs.joc.9b02107