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Solution versus solid-state structure of ytterbium heterobimetallic catalysts.
Lorenzo Di Bari1, Moreno Lelli, Guido Pintacuda
1ICCOM-CNR, Sez. di Pisa, Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35, I-56126 Pisa, Italy.
Journal of the American Chemical Society
|May 2, 2003
Summary
This study reveals the solution structures of ytterbium heterobimetallic complexes, finding they share similar geometries but differ in magnetic properties. Near-IR circular dichroism proves sensitive to changes in the ytterbium coordination sphere.
Area of Science:
- Organometallic Chemistry
- Catalysis
- Spectroscopy
Background:
- Ytterbium heterobimetallic complexes, including Na(3)[Yb((S)-BINOL)(3)], K(3)[Yb((S)-BINOL)(3)], and Li(3)[Yb((S)-BINOL)(3)], are recognized enantioselective catalysts.
- Understanding their solution structures is crucial for optimizing catalytic performance.
Purpose of the Study:
- To elucidate the solution structures of ytterbium heterobimetallic complexes.
- To investigate the structural dynamics upon dissolution from crystalline states.
- To assess the sensitivity of spectroscopic techniques to coordination sphere changes.
Main Methods:
- Nuclear Magnetic Resonance (NMR) spectroscopy, including paramagnetic shifts.
- UV and near-infrared (NIR) circular dichroism (CD) spectroscopy.
- X-ray Diffraction (XRD) for crystalline structure comparison.
- Exchange Spectroscopy (EXSY) to study bond lability.
Main Results:
- Complexes 1, 2, and 3 exhibit identical solution geometries but distinct magnetic susceptibility anisotropy (D) factors.
- A structural rearrangement from crystalline C(3) to solution D(3) symmetry was observed for complex 1 upon dissolution.
- Ytterbium-oxygen bonds to water were not detected in solution, and Ln-BINOL bonds demonstrated lability.
- NIR-CD spectroscopy is highly sensitive to alterations in the ytterbium coordination environment.
Conclusions:
- The solution structures of these ytterbium complexes are conserved across different counterions (Na+, K+, Li+).
- Dissolution induces a symmetry change from crystalline to solution states.
- The lability of Ln-BINOL bonds and the absence of water coordination are key solution-state features.
- NIR-CD is a powerful tool for probing the ytterbium coordination sphere in these catalytic systems.
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