Asymmetric metal complex catalysis in the series of monofunctional substrates: the lower the catalyst symmetry, the higher the enantioselectivity

The title statement is derived from analysis of 90 asymmetric reactions (addition, reduction, oxidation, etc.) of monofunctional substrates such as benzaldehyde, acetophenone or thioanisole catalyzed by metal complexes with C₁-, C₂- and C₃-symmetric chiral ligands. The advantage of complexes with C₁-symmetric ligands is manifested as higher ee values of the reaction products compared with C₂ complexes as catalysts (the average ee values are 97% and 85%, respectively). The possible catalytic cycles of effective asymmetric reactions under the action of C₂-complexes proposed by different authors attest to C₁ symmetry of the key intermediate that controls the asymmetric induction. If the key intermediate retains the initial C₂ symmetry, the reaction enantioselectivity is usually low.