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BINOL as a Chiral Solvating Agent for Sulfiniminoboronic Acids
Robin R Groleau1, Robert S L Chapman1, John P Lowe1
1Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
Analytical Chemistry
|November 6, 2023
Summary
Chiral solvating agent (CSA) NMR studies reveal concentration-dependent shifts in sulfiniminoboronic acid (SIBA) analysis. Using both BINOL enantiomers is recommended to avoid misassignments in enantiopurity determination.
Area of Science:
- Organic Chemistry
- Analytical Chemistry
- Spectroscopy
Background:
- Chiral solvating agents (CSAs) like BINOL are used to determine enantiopurity.
- Sulfiniminoboronic acids (SIBA) are chiral compounds whose enantiopurity is often assessed using NMR.
Purpose of the Study:
- To investigate the influence of BINOL as a CSA on the 1H NMR chemical shifts of SIBA.
- To elucidate the structural basis for observed NMR signal variations.
Main Methods:
- 1H NMR spectroscopy
- 11B/15N NMR spectroscopy
- X-ray crystallography
- 1H NMR NOESY experiments
Main Results:
- Observed concentration- and enantiopurity-dependent chemical shift variations in SIBA imine protons.
- BINOL-SIBA assemblies lack N-B coordination bonds; H-bonding networks drive the observed effects.
- Potential for diastereomeric signal overlap leading to enantiopurity misassignments.
Conclusions:
- Hydrogen-bonding interactions between BINOL and SIBA are responsible for NMR signal variations.
- Recommend using both BINOL enantiomers in 1H NMR protocols to accurately determine SIBA enantiopurity.
- This approach mitigates risks of misassignment due to concentration or enantiomeric ratio effects.
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