One-Step Process for the Regiodivergent Double Hydrocyanation of 1,3-Butadiene

In industry, the two important nitrile starting materials, adiponitrile and 2-methylglutaronitrile, are primarily manufactured through the well-known DuPont process, which consists of a tandem sequence including first hydrocyanation, isomerization and second hydrocyanation. However, this mature process has the intrinsic defects of step efficiency and regioselectivity. Herein, we report a nickel-catalyzed divergent, one-step double hydrocyanation of 1,3-butadiene to produce either adiponitrile or 2-methylglutaronitrile in high regioselectivity. The key to this success lies in the highly tunable binding pockets of the bidentate phosphite ligands, which creates a geometrically defined coordination space around the nickel center. The first hydrocyanation that produces either the linear or branched alkenyl nitrile was identified as the selectivity-determining step. Organometallic studies confirm the formation of well-defined diphosphite nickel diene complexes in solution, and the role of ligands in dictating regioselectivity was further rationalized by DFT computations. This result provides the first example of a highly selective nickel-catalyzed synthesis of adiponitrile and 2-methylglutaronitrile from butadiene, and it also represents a high-level of catalyst-controlled regioselectivity via the fine-tuning of ligand pocket geometry.