Planar- and central-chiral N,O-[2.2]paracyclophane ligands:: Non-linear-like effects and activity

The non-linear-like effect (NLLE), activity, temperature dependence, and kinetics of hydroxy[2.2]paracyclophane ketimine ligands have been investigated with the 1,2-addition reaction of diethylzinc to cyclohexanecarbaldehyde. A linear correlation between the enantiomeric excess of AHPC ketimine ligands bearing a phenylethyl side group and the product was observed with 0.5 mol % of catalyst loading. On increasing the catalyst loading to 4 mol %, a precipitate of the inactive heterochiral species was formed and resulted in a positive nonlinear-like effect. The enantiomeric ratio was found to have linear temperature dependence.