Resolution of Seven‐Coordinate Complexes

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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.