Structural, magnetic and catalytic properties of a self-recognized mu-oxo-bridged diiron(III) bis(benzimidazole) complex.

The inherent nonplanarity and C(2) symmetry of the dimethyl-substituted bis(benzimidazole) ligand (Me(2)BBZ) results in two distinct atropisomers that, when separated, have been suggested to have potential for chiral recognition and catalysis. Here is reported the synthesis and characterization of a diiron mu-oxo-bridged bis(benzimidazole) complex, 1, that provides indirect support for this hypothesis. Dimerization of a racemic solution of iron-Me(2)BBZ monomers via the mu-oxo bridge yields (+,+) and (-,-) diastereomers whose complementary association can be attributed to the inherent sidedness of the metal-Me(2)BBZ interaction surface, and to the differences in the torsional angles of the phenyl(benzimidazole) units (34 degrees) and the Schiff base linkages (54 degrees). These results highlight the steric differences between the phenyl(benzimidazole) and Schiff-base portions of the ligand, features that could be important in the chiral recognition of ligands and in differentiating substrate trajectories as required for asymmetric catalysis. For completeness, studies of 1 in the catalytic epoxidation of styrene are also reported.