Binaphthol-based diphosphite ligands in asymmetric nickel-catalyzed hydrocyanation of styrene and 1,3-cyclohexadiene : influence of steric properties

A series of chiral (R)-binaphthol-based diphosphite ligands with different substituents was prepared and applied in the asymmetric nickel-catalyzed hydrocyanation of styrene and 1,3-cyclohexadiene to investigate the influence of their steric properties. The optimum steric properties for the hydrocyanation reaction lie within a narrow window. With the optimized ligand, hydrocyanation of styrene gave full conversion (Subs/Ni=100) with 49 % ee, the TON was determined to be 600. Hydrocyanation of 1,3-cyclohexadiene gave 50 % conversion (Subs/Ni=500) with an excellent ee of 86 %. This demonstrates that high ees are not only accessible for vinylarenes but also for conjugated dienes in the asymmetric nickel-catalyzed hydrocyanation.