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Published on: November 12, 2016
Solvent effects on one-bond B-Li coupling constants in boryllithium compounds.
Janet E Del Bene1, José Elguero
1Department of Chemistry, Youngstown State University, Youngstown, Ohio 44555, USA. jedelbene@ysu.edu
Magnetic Resonance in Chemistry : MRC
|April 20, 2007
Summary
Computational chemistry reveals solvent effects on boron-lithium NMR properties. Solvation increases ion-pair character, decreasing B-Li coupling constants and shifting boron chemical shifts toward experimental values.
Area of Science:
- Computational Chemistry
- Nuclear Magnetic Resonance (NMR) Spectroscopy
- Organometallic Chemistry
Background:
- Nuclear magnetic resonance (NMR) spectroscopy is crucial for characterizing chemical structures and bonding.
- Discrepancies exist between computed and experimental NMR parameters for boryllithium compounds, particularly concerning the influence of solvent.
- Understanding these discrepancies is key to accurately interpreting NMR data for reactive organometallic species.
Purpose of the Study:
- To compute B-Li coupling constants and B chemical shifts for Li-diazaborole and its complexes with solvent molecules.
- To investigate the impact of solvent (H2O, FLi) on the electronic structure and NMR properties of Li-diazaborole.
- To resolve discrepancies between theoretical calculations and experimental NMR data for boryllithium species.
Main Methods:
- Equation-of-Motion Coupled-Cluster Singles Doubles (EOM-CCSD) calculations were employed.
- NMR properties, including 1J(B-Li) coupling constants and B chemical shifts, were computed.
- A model compound, H(2)BLi, was studied with varying numbers of solvent molecules.
Main Results:
- The ion-pair character of the B-Li bond increases with the addition of solvent molecules.
- The B-Li coupling constant (1J(B-Li)) decreases systematically with increasing solvent basicity and number.
- Boron chemical shifts for Li-diazaborole approach experimental values in the presence of even one solvent molecule.
Conclusions:
- Solvent molecules significantly influence the B-Li bond character and NMR properties.
- Computed NMR parameters for Li-diazaborole in the presence of solvent align better with experimental observations.
- The study highlights the critical role of solvation in determining NMR spectroscopic parameters for boryllithium compounds.
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