Brominated Pd‐on‐Au Nanostructures Enable Reductive Relay Isomerization of Alkynes to <i>E</i> ‐alkenes

Abstract

Abstract Achieving stereoselective alkyne semi‐hydrogenation to E ‐alkenes remains a persistent challenge due to inherent limitations of conventional catalysts in controlling stereochemistry and suppressing over‐hydrogenation. Herein, we resolve this fundamental dilemma through a rationally designed brominated Pd‐on‐Au nanocatalyst (Pd 0.03 ‐Br 1 ^Au/TiO 2 ) featuring spatially segregated active sites operating via reductive relay isomerization. This sophisticated architecture enables unprecedentedly efficient E ‐alkene synthesis (&gt;96% selectivity for trans ‐stilbene at near‐quantitative conversion). Fabricated by sequentially depositing Au nanoparticles on TiO 2 , with tiny Pd loading on Au, and controlled surface bromination, the catalyst leverages synergistic cooperativity: The TiO 2 –Au interface primarily activates formic acid (FA) to generate reactive surface‐bound hydride species (H*) while minimizing unproductive H 2 formation; concurrently, atomically dispersed Pd 1 sites on Au nanoparticles exclusively mediate rapid Z ‐to‐ E isomerization, whereas bromide‐capped Pd nanoclusters kinetically regulate FA dissociation kinetics at TiO 2 –Au interface and sterically block overhydrogenation adsorption geometries. This spatially orchestrated multisite system decisively overcomes classical activity–selectivity trade‐offs, establishing a universally applicable framework for decoupling and optimizing individual catalytic functions in heterogeneous design. Our work delivers both a sustainable strategy for scalable trans ‐alkene production and fundamental mechanistic insights into complex cooperative reaction networks.