Non-Linear Effects in Asymmetric Catalysis: Impact of Catalyst Precipitation

Non-linear effects between the enantiomeric excesses of both the ligand and the product are ubiquitous phenomena in asymmetric catalysis, allowing asymmetric amplification (or depletion) and are widely used tools for mechanistic investigations. Non-linear effects are caused by catalyst aggregation; however, the effect of catalyst precipitation on NLEs has not been systematically investigated to date, except in special cases such as ternary phase systems. In this article, we show through simulations and with several literature cases at hand how precipitation affects shape and amplitude of NLE curves. The limit of solubility of the homo- or heterochiral dimeric species causes broken-shaped NLE curves or very pronounced NLEs even though the equilibria between the different species in solution are not favorable, at first sight. Peculiar features such as horizontal segments, inverse S-shaped curves and a strong effect of total catalyst concentration are also observed. Overall, this study allows to get a better understanding of chiral catalytic systems and gives an outlook at other types of phase separation leading to NLEs.