Coordination-Sphere Control of H2 Activation and Halide-Assisted Inner-Sphere C-C Bond Formation at Formally d10...

How formally d10 Cu(I) centers activate H2 and channel the resulting hydride reactivity into selective C-C bond formation without conventional two-electron redox cycling remains an important mechanistic question in inorganic chemistry. Density functional theory calculations elucidate the Cu(I)-catalyzed hydrogenative coupling of alkynes with allylic chlorides. Ligand-assisted heterolytic H2 cleavage generates a Cu-H species through an endergonic, reversible pre-equilibrium, making hydride formation a key thermodynamic entry point to the productive manifold. Across a representative but limited ligand series, the H2-cleavage barrier follows a Brønsted-Evans-Polanyi-type relationship with the Gibbs energy of Cu-H formation, indicating that ligand effects are transmitted mainly through hydride stabilization within this set. Hydrocupration is the first product-committing and stereoselectivity-determining step and is governed by steric organization and σ(Cu-H) → π*(alkyne) donor-acceptor interaction. Subsequent C-C bond formation preferentially follows a chloride-assisted inner-sphere pathway rather than an outer-sphere SN2-type mechanism because chloride participation preorganizes the electrophile, reduces structural reorganization, and attenuates Pauli repulsion. These results establish how ligand environment, hydride thermodynamics, and halide coordination jointly regulate small-molecule activation and selective bond formation at formally d10 Cu(I) centers.