Stereodivergent, Kinetically Controlled Isomerization of Terminal Alkenes via Nickel Catalysis

Because internal alkenes are more challenging synthetic targets than terminal alkenes, metal‐catalyzed olefin mono‐transposition (i.e., positional isomerization) approaches have emerged to afford valuable E‐ or Z‐ internal alkenes from their complementary terminal alkene feedstocks. However, the applicability of these methods has been hampered by lack of generality, commercial availability of precatalysts, and scalability. Here, we report a nickel‐catalyzed platform for the stereodivergent E/Z‐selective synthesis of internal alkenes at room temperature. Commercial reagents enable this one‐carbon transposition of terminal alkenes to valuable E‐ or Z‐internal alkenes via a Ni−H‐mediated insertion/elimination mechanism. Though the mechanistic regime is the same in both systems, the underlying pathways that lead to each of the active catalysts are distinct, with the Z‐selective catalyst forming from comproportionation of an oxidative addition complex followed by oxidative addition with substrate and the E‐selective catalyst forming from protonation of the metal by the trialkylphosphonium salt additive. In each case, ligand sterics and denticity control stereochemistry and prevent over‐isomerization. The nickel‐catalyzed kinetic alkene mono‐transposition generates E‐ or Z‐olefins depending on the steric properties and denticity of the ligand employed. Mechanistic studies reveal that the aryl iodide additive acts as a redox buffer for nickel in the Z‐selective reaction, generating the most‐selective NiII–H that outcompetes a less Z‐selective NiI–H species. For the E‐selective reaction, the phosphonium salt plays a dual role as an acid and ligand, forming a phosphine‐bound cationic Ni−H catalyst in situ.