Markovnikov-Selective Electrocatalytic Hydroalkylation Enabled by Metal-Ligand Cooperative Storage of H-Atom Equivalents

Abstract

The synthesis of 1,1-disubstitued olefins is an important transformation that classically uses strategies like Wittig chemistry or cross coupling reactions. Here, we introduce an electrochemical method for the selective hydroalkylation of terminal alkynes to generate a variety of 1,1-disubstituted olefins. This approach utilizes a dihydrazonopyrrole Ni complex capable of storing an H₂ equivalent (2H⁺ + 2e^-) on the ligand backbone. This mild reaction uses electricity and a weak acid and thus tolerates amine and ketone functional groups which are sensitive to classic Wittig conditions. Mechanistic studies reveal the essential role of the ligand steric environment in dictating product regioselectivity. Calculations support an outer sphere alkyl radical addition instead of a Ni-centered reductive elimination mechanism which is commonly invoked for transition metal hydroalkylation catalysts. Beyond its unique functional group compatibility, the scope of this reaction includes primary and secondary alkyl iodide electrophiles along with unactivated alkyne substrates. These findings underscore how metal-ligand cooperativity, particularly with ligand-based storage of protons and electrons, supports catalytic platforms which can be tuned for varied electrosynthetic applications beyond hydrogenation.

Keywords: alkyne functionalization; coupling; electrosynthesis; hydroalkylation; radical reactivity.