Self-recognition based on atropoisomerism with new chiral bidentate ligands and Copper(I)

A new family of atropoisomeric bidentate ligands that have a dissymmetric b enzimidazole-pyridine binding site has been synthesized. Aromatic rings, th at is, naphthyl, tolyl, and cumyl, were introduced in order to fine tune th e complexation properties of the ligands. The tetrahedral copper(I) complex es L2Cu were prepared and the structure of the complex with the naphthyl-su bstituted ligand was established by X-ray diffraction. The behavior of the L2Cu complexes in solution was studied by H-1 NMR spectroscopy. With the mo st crowded cumyl-derived ligand, ligand self-recognition based on chirality occured: 95% of the complex was present in solution as a racemate RR Delta /SS Lambda, the heterochiral RS Delta/SR Lambda isomers represented only 5% of the mixture, and the RR Lambda/SS Delta isomers were not detected. Owin g to lower steric repulsions within the other L2Cu complexes (i.e.,with the naphthyl- and tolyl-based ligands) the homorecognition is less pronounced, as diastereomeric excesses of 6 and 26% were measured, respectively.