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.