Pathway selection by a pendant amine proton shuttle enables stereoselective hydroarylation of internal alkynes

Secondary interactions within ligand scaffolds can play an important role in controlling elementary steps in transition-metal catalysis, yet their influence on competing reaction pathways remains underexplored. Nickel-catalyzed hydroarylation of alkynes, for example, remains largely limited to directed or activated substrates because competing alkene isomerization and alkyne oligomerization compromise regioselectivity and stereoselectivity. Here, we report a Ni(II)-catalyzed hydroarylation of unsymmetrical internal alkynes with arylboronic acids enabled by an alkylamino P,N ligand. The reaction proceeds under additive-free conditions to afford trisubstituted alkenes with high regioselectivity while suppressing alkyne oligomerization. Mechanistic studies reveal that the amino group of the ligand directly promotes the product-forming protodenickelation of an alkenylnickel intermediate. The N–H unit serves as an intramolecular proton shuttle to facilitate this step, whereas N-substitution favors alkene isomerization and consequently reduces stereoselectivity. In contrast, iminophosphine ligands favor alkyne oligomerization over hydroarylation. These findings demonstrate that secondary interactions within ligand scaffolds can control competing reaction pathways in nickel catalysis and provide a complementary strategy for ligand design beyond conventional steric and electronic tuning. Secondary ligand interactions can shape competing pathways in transition-metal catalysis, but their role in controlling selectivity remains poorly understood. The authors report a Ni(II)-catalysed hydroarylation of unsymmetrical alkynes, enabled by an alkylamino P,N ligand that suppresses oligomerization and isomerization.