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Updated: Jan 2, 2026
Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex
Published on: July 27, 2022
Controlling dinitrogen functionalization at rhenium through alkali metal ion pairing
Trevor D Lohrey1, Robert G Bergman2, John Arnold1
1Department of Chemistry, University of California, Berkeley, CA 94720, USA. arnold@berkeley.edu and Chemical Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA.
Sodium ions in a rhenium(I) salt are crucial for forming rhenium(III)-diazenide complexes from dinitrogen. This ion pairing effect significantly impacts nitrogen fixation and related π-acid activation chemistry.
Area of Science:
- Organometallic Chemistry
- Inorganic Chemistry
- Coordination Chemistry
Background:
- Rhenium complexes are investigated for their potential in nitrogen fixation and catalysis.
- The role of counterions and ion pairing in stabilizing reactive intermediates is crucial in organometallic chemistry.
Purpose of the Study:
- To investigate the formation of rhenium(III)-diazenide complexes from a rhenium(I) precursor under a dinitrogen atmosphere.
- To determine the critical role of sodium (Na+) ion pairing in facilitating dinitrogen binding and activation.
- To explore the impact of ion pairing on the activation of other π-acid ligands like carbon monoxide and isocyanides.
Main Methods:
- Synthesis and characterization of rhenium(I) complexes, specifically Na[Re(η⁵-Cp)(BDI)].
- Reactions conducted under dinitrogen atmosphere at low temperatures.
- Comparative studies using benzo-12-crown-4 to sequester the Na+ ion.
- Investigation of analogous reactions with carbon monoxide (CO) and 2,6-xylylisocyanide (XylNC).
- Structural and spectroscopic analyses (e.g., X-ray crystallography, NMR, IR spectroscopy) to elucidate bonding and reactivity.
Main Results:
- Selective formation of rhenium(III) centers bound to diazenide fragments was achieved by cooling the Na[Re(η⁵-Cp)(BDI)] salt under N2.
- Dinitrogen binding was significantly less favorable when the Na+ ion was sequestered, highlighting the importance of ion pairing.
- Analogous studies with CO and XylNC provided structural and spectroscopic data, offering insights into ion-pairing effects on π-acid activation.
Conclusions:
- Ion pairing involving the Na+ counterion is essential for the efficient activation of dinitrogen by the [Re(η⁵-Cp)(BDI)] complex.
- The findings provide a fundamental understanding of how counterion effects influence the reactivity of metal complexes with small molecules.
- This study contributes to the development of strategies for controlling metal-ligand interactions and activating challenging substrates like N2.
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