Elucidation of key factors in nickel-diphosphines catalyzed isomerization of 2-methyl-3-butenenitrile

Abstract

The phosphorus (III) ligands were crucial for the further improvement of homogeneous nickel catalysts that were employed in the isomerization of 2-methyl-3-butenenitrile (2M3BN) to 3-pentenenitrile (3PN). The catalytic behavior of 1,4-bis(diphenylphosphino)butane (dppb1dppb: 1,4-bis(diphenylphosphino)butane; dppe:1,2-bis(diphenylphosphino)ethane; dppp3:1,3-bis(diphenylphosphino)propane; dppp5:1,5-bis(diphenylphosphino)pentane; dpph:1,6-bis(diphenylphosphino)hexane; dcpb: 1,4-Bis(dicyclohexylphosphino)butane.1)Ni complex was improved in cumene and the conversion of 2M3BN showed zero-order kinetic. The mechanism behind the isomerization was amended and the density functional theory (DFT) calculations suggested that the reductive elimination step forming 3PN was kinetically relevant in catalytic cycles. An optimal bite angle of nickel-diphosphine complex around 104.7° provided excellent catalytic performance. The key factors governing isomerization were unraveled. The steric effect determined the reactivity, while the electronic effect governed the selectivity of the isomerization reaction. The bite angle – a vital descriptor – would associate with the steric and electronic effects of diphosphines. These structure-activity relationships provided important guidance for ligand design in the isomerization of 2M3BN.