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Tuning Cobalt(II) Phosphine Complexes to be Axially Ambivalent.
Jack Thomas-Colwell1, Arvin Sookezian1, Daniel A Kurtz2
1Department of Chemistry, Occidental College, Los Angeles, California 90041, United States.
Inorganic Chemistry
|August 3, 2022
Summary
Researchers isolated and characterized three cobalt(II) bis(phosphine) complexes, revealing diverse axial ligand coordination. Complex 1 is a rare square-planar cobalt(II) species, highlighting a shallow energy landscape for axial ligation.
Area of Science:
- Coordination Chemistry
- Organometallic Chemistry
- Materials Science
Background:
- Cobalt(II) complexes with phosphine ligands are crucial in catalysis.
- Understanding axial ligand behavior is key to catalyst design.
- Exploring diverse coordination geometries in metal complexes is fundamental.
Purpose of the Study:
- To synthesize and characterize a series of cobalt(II) bis(phosphine) complexes with varying axial ligands.
- To investigate the structural diversity and electronic properties of these complexes.
- To explore the lability of axial ligands for catalyst design.
Main Methods:
- X-ray crystallography for structural determination.
- Electron Paramagnetic Resonance (EPR) spectroscopy.
- UV-visible spectroscopy.
- Ligand field angular overlap model (LF-AOM) calculations.
Main Results:
- Isolation and structural characterization of three cobalt(II) complexes: [Co(dppv)2][BF4]2 (1), [Co(dppv)2(NCCH3)][BPh4]2 (2), and [Co(dppv)2(NCCH3)2][BF4]2 (3).
- Complex 1 represents a rare example of a square-planar cobalt(II) complex with only neutral, bidentate ligands.
- EPR and UV-visible spectroscopy, supported by LF-AOM calculations, indicate a shallow energy landscape for axial ligation.
Conclusions:
- The study reveals multiple crystallization motifs for cobalt(II) complexes with identical phosphine ligands.
- A shallow energy landscape for axial ligation was confirmed, suggesting lability.
- A strategy for tuning axial lability on phosphine scaffolds is proposed for designing cobalt phosphine catalysts for oxidation and reduction reactions.
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