Resolution of seven-coordinate complexes |
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Authors: | Lennartson Anders Vestergren Marcus Håkansson Mikael |
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Institution: | Department of Chemistry, G?teborg University, 41296 G?teborg, Sweden. |
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Abstract: | The crystal structures of Pr(dbm)3H2O] (1), Sm(dbm)3H2O] (2), and Er(dbm)3H2O] (3) have been determined (dbm=dibenzoylmethane). They display seven-coordinate propeller-shaped molecules, which are chiral and crystallize as conglomerates in space group R3. Analysis of the crystal structures reveals supramolecular interactions, including formation of a quadruple helix, which explain how stereochemical information can be transferred between stacks of molecules. A method to quantify the ee in bulk samples of stereochemically labile compounds by using solid-state CD spectroscopy is described. Using this method, it has been shown that compounds 1-3 undergo total spontaneous resolution directly after synthesis, forming a microcrystalline reaction product that is essentially enantiopure. The resolution of bulk quantities of seven-coordinate complexes (without chiral or polydentate ligands) is thus reported for the first time. Because the crystallization starts without seeding, the overall preparation may be regarded as absolute asymmetric synthesis. |
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Keywords: | asymmetric synthesis chiral resolution chirality circular dichroism lanthanides |
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