Induced of axial chirality in near-infrared-absorbing ball-shaped ruthenium complexes

Ball-shaped metal complexes that absorb in the near-infrared (NIR) region can be synthesized in a single step. Although stereogenic-at-metal complexes have been obtained, the induction of axial chirality has not yet been demonstrated. In this study, NIR-absorbing ball-shaped ruthenium complexes with axial chirality were facilely synthesized using asymmetric diiminoisoindoline derivatives. Despite lacking a discrete point chiral moiety, these complexes exhibited molecular chirality. The incorporation of bulky substituents facilitated enantiomeric differentiation. High-performance liquid chromatography (HPLC) with a chiral column enabled the isolation of the pure enantiomers as stable compounds. The absolute configurations of these isomers were revealed using vibrational circular dichroism (VCD) spectroscopy. The characteristic peaks originating from ligand vibrations exhibited distinct mirror images, and the experimental spectra were well reproduced by theoretical calculations. This methodology has broad applicability for the development of chiral ball-shaped metal complexes as NIR materials.