Driving Efficient Tandem Catalysis by Coupling Distinct Active Sites within a Ternary Hydride Lattice

Tandem catalysis depends critically on communication between functionally distinct active sites to orchestrate multistep reactions. Atomic-scale integration of such complementary sites would facilitate seamless intersite communication and efficient mass/energy transfer, yet remains elusive in heterogeneous tandem catalysis owing to intrinsic challenges of catalyst architecture engineering. Herein, we report K₃PdH₅, a ternary palladium hydride, with two distinct [PdH₄] and [KH] lattice sites, which catalyzes tandem semihydrogenation-isomerization of internal alkynes with exceptionally high activity and selectivity, achieving (E)-alkene formation rates up to 2 orders of magnitude higher than existing systems. Mechanistic studies disclose that the [PdH₄] site exhibits moderate alkyne/alkene chemisorption while impedes H₂ activation, allowing semihydrogenation to (Z)-alkene; the basic [KH] site, on the other hand, drives (Z) → (E) isomerization to proceed via a delocalized π-allyl species stabilized by K cation-π interactions. By atomic-level coupling of these two-type active sites within one single lattice, K₃PdH₅ demonstrates a unique function mechanism that is inaccessible to conventional heterogeneous tandem catalysts.