Investigations of Racemic and Quasiracemic Metal Complexes of Substituted Benzoylalanines with Copper Using Pyridine Ligands

Two chemically distinct molecules of opposite handedness can cocrystallize together to produce a quasiracemate. Many quasiracemates consist of a molecule with R configuration at a chiral center paired with a second molecule with an S configuration at an identical chiral center, but with a functional group elsewhere in the molecule replaced with a different substituent of similar size. The two molecules usually assemble about a pseudo center of symmetry. This approximately centrosymmetric relationship in the quasiracemate usually mimics the arrangement of the enantiomers in the true racemates of either of the components of the quasiracemate. Most work on quasiracemates has used organic molecules using carboxylic acids to form inversion-related cyclic dimers. Square planar metal complexes likewise bring together ligands in a centrosymmetric arrangement. We have been exploring copper(II) as an inversion center to prepare quasiracemate-like complexes. Previous work prepared copper(II) complexes using substituted benzoylalanines (-NO2, -Cl, -CH3, and -Br substituents) as the racemic or quasiracemic ligands. These structures have a copper center which is four coordinate with two benzoylalanine ligands and two N-methylimidazole ligands. In this work, we are attempting to prepare new copper complexes using pyridine instead of N-methylimidazole. Preliminary results have produced some promising crystals. Crystal structures will be described and compared to previous results.