Cooperative hydrogenation catalysis at a constrained gallylene-nickel(0) interface

The discovery of unique mechanisms in 3d metal catalysis is of paramount importance in utilizing these Earth-abundant metals in place of scarce precious metals. Inspired by the Horiuti-Polanyi mechanism at play in heterogeneous hydrogenation catalysts, we describe a bimetallic molecular catalyst that can selectively semi-hydrogenate alkynes via a ligand-to-substrate hydride transfer mechanism. This mimics established heterogeneous mechanisms in which remote surface-bound hydride ligands undergo a similar reactive process. This is achieved through the development of a chelate-constrained gallium(I) ligand, which operates in concert with nickel(0) to (reversibly) cleave H₂, generating a [GaNi] 1,2-dihydride complex that is found to be the resting state in the catalytic process. This discovery takes steps toward utilizing non-innocent low-valent group 13 centers in effective cooperative catalysis, opening new mechanistic pathways that may aid in employing Earth-abundant metals in key catalytic transformations.