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

The synthesis of 1,1-disubstituted
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 a 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.