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Inherently chiral uranyl-salophen macrocycles: computer-aided design and resolution.
Antonella Dalla Cort1, Luigi Mandolini, Chiara Pasquini
1Dipartimento di Chimica and IMC-CNR Sezione Meccanismi di Reazione, Università La Sapienza, Box 34 Roma 62, 00185 Roma, Italy. antonella.dallacort@uniroma1.it
The Journal of Organic Chemistry
|November 19, 2005
Summary
Researchers designed new uranyl-salophen compounds by adding polymethylene bridges to prevent flipping and fast enantiomerization. This approach creates robust chiral macrocycles, overcoming limitations of previous methods for chiral separation.
Area of Science:
- Coordination Chemistry
- Supramolecular Chemistry
- Organic Synthesis
Background:
- Uranyl-salophen compounds exhibit a flipping motion that inverts their structure, leading to rapid enantiomerization in derivatives.
- Previous attempts to slow this process using bulky substituents caused ligand distortions and complex dissociation during purification.
Purpose of the Study:
- To design and synthesize robust, nonflipping uranyl-salophen compounds.
- To overcome the dissociation issue encountered with bulky substituents during chromatographic purification.
- To develop a new strategy for creating stable chiral uranyl-salophen macrocycles.
Main Methods:
- Molecular mechanics calculations to predict optimal polymethylene bridge lengths.
- Synthesis of uranyl-salophen macrocycles bridged with 12- and 13-methylene chains.
- Chiral High-Performance Liquid Chromatography (HPLC) for resolving enantiomers.
Main Results:
- Molecular mechanics indicated that polymethylene chains of 12 and 13 units best fit the gap between phenoxide rings without distorting the ligand.
- Chiral uranyl-salophen macrocycles bridged with 12- and 13-methylene chains were successfully synthesized in good yields.
- The synthesized macrocycles were effectively resolved into their respective enantiomers using chiral HPLC.
Conclusions:
- Connecting the para positions of uranyl-salophen compounds with suitable polymethylene bridges effectively blocks the flipping motion.
- This bridging strategy provides a robust method for synthesizing stable chiral uranyl-salophen macrocycles.
- The developed compounds and methods offer a viable alternative for accessing enantiomerically pure uranyl-salophen derivatives.