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Absolute Asymmetric Synthesis: Viedma Ripening of [Co(bpy)3](2+) and Solvent-Free Oxidation to [Co(bpy)3](3.)
Per Martin Björemark1, Johan Jönsson1, Mikael Håkansson2
1Department of Chemistry and Molecular Biology, University of Gothenburg, 412 96 Gothenburg (Sweden).
Abstract:
Syntheses of [Co(bpy)3](2+) yield racemic solutions because the Δ- and Λ-enantiomers are stereochemically labile. However, crystallization and attrition-enhanced deracemization can give homochiral crystal batches of either handedness in quantitative yield. Subsequently, solvent-free oxidation with bromine vapour fixes the chirality because [Co(bipy)3](3+) does not enantiomerize in solution at ambient temperature. This combination of Viedma ripening and the labile/inert Co(II)/Co(III) couple constitutes a convenient method of absolute asymmetric synthesis.
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