Mechanistic Investigation On Hydrocyanation Of Butadiene: A Dft Study

The nickel-catalyzed addition of Hydrocyanic acid (HCN) to butadiene usually leads to a mixture of the branched 2-methyl-3-butenenitrile (2M3BN) and the linear 3-pentenenitrile (3PN) with a 30:70 ratio by employing mono-dentate phosphites, while a 97% selectivity to 3PN is obtained using a 1,4-bis(diphenyphosphino)butane (dppb) ligand and Ni(COD)(2)(1,5-Cyclooctadiene) as catalysts. To explain this phenomenon, a reasonable mechanism of the hydrocyanation, involving the cyano (CN) migration (for 3PN) and the methylallyl rotation (for 2M3BN) pathways, is proposed. The key intermediates and the rate-determining steps in the pathways have been illustrated. The methylallyl rearrangement is the rate-determining step in the formation of 3PN while the reductive elimination governs the reaction to 2M3BN, which is subsequently isomerized to 3PN. Moreover, the opposite changes of the bite angle of the intermediates and transition states explain how the reactions proceed in two different directions.