Mechanisms of β,γ-Unsaturated Nitriles From Alkenes and Acetonitrile, Catalyzed by Cu/Ni or TBPB? A DFT Investigation

The mechanisms for the cyanomethylation of alkenes with acetonitrile were investigated using the M06-L-D3/ma-def2-SVP method (“ma-def2-SVP” indicates that diffuse functions have been added to the def2-SVP basis set). The solvation model based on density (SMD), which is based on solute electron density, was employed to simulate the solvent effect. Computational results reveal that tert-butyl peroxybenzoate (TBPB) acts as a radical initiator, undergoing homolysis to generate t-BuO• and PhCOO• radicals. Additionally, CuX₂ (X = OTf) and NiCl₂(DME) serve as effective catalysts to accelerate this process. The addition reactions between t-BuO• (or PhCOO•) radical and 1,1-diphenylethylene exhibit lower energy barriers, leading to complete C (sp³)-H activation of acetonitrile unsuccessful. C (sp³)-H activation can be completed by CuX₂(X = OTf), forming •CH₂-CN-CuX radical. These radicals and reaction intermediates undergo SN2 reactions to regenerate t-BuO• and PhCOO• radicals. Meanwhile, the selective addition reactions between •CH₂-CN-CuX radical and 1,1-diphenylethylene suggest that C3 atom is the first choice and IRI (interaction region indicator) analysis reveals that vdW (van der Waals) interactions play an important role in the choice for the reactive site; finally, the product intermediate can be generated in large amounts, which could have some paths to yield the final product 4,4-diphenylbut-3-enenitrile (P). Yet, the t-BuO• radical, PhCOO^• radical, CuX₂(X = OTf), and NiCl₂(DME) could be used to finish the reactions. The Gibbs free energy surfaces show that the path with the participation of PhCOO• radicals is optimal. The mechanisms of the byproduct have also been explored. Both these calculations agree with the experimental results. The IRI analysis reveals that the weak interaction can help to reduce the energy barriers.