title: Crystal chemistry of VAPOL.
abstract: Ligands employed in enantioselective catalysis are capable of displaying rich phase behavior that can significantly impact their properties, both structural and physical. To illuminate these issues in a model system, the solid-state structure and properties of the vaulted biaryl ligand VAPOL were investigated. Racemic VAPOL and solvates with toluene and ethyl acetate were structurally characterized. In addition, two polymorphs of (S)-VAPOL were found, and the crystal packing in these and a very stable CH(2)Cl(2) solvate was elucidated. In contrast to BINOL, the unsolvated forms of the ligand lack classical hydrogen-bonding motifs. Remarkably, the melting point of racemic VAPOL is 86 degrees C higher than that of (S)-VAPOL form I, and there is a 2.0 kcal/mol difference in stability at room temperature, favoring the racemate. These values are at the upper end of those observed in the literature for differences between a racemic/chiral pair.
authors.affiliation: Department of Chemistry and the Macromolecular Science and Engineering Program, The University of Michigan, Ann Arbor, Michigan 48109-1055, USA.
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Price
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Matzger