Designing Synergistic Nanocatalysts for Multiple Substrate Activation: Interlattice Ag–Fe₃O₄ Hybrid Materials for CO₂‑Inserted Lactones

Multimetallic architectures that combine chemically diverse materials to affect tandem reactions within a single scaffold drive future nanocatalyst development. Here, we show the unique, interlattice growth of the small molecule activating Ag⁰ guest within the Lewis acidic/basic Fe₃O₄ octahedral host (Fe₃O₄@Ag-40, 10, 6, 2 at %) via a polyol-hydrothermal procedure. Microscopic (scanning electron microscopy and energy-dispersive X-ray spectroscopy ) and structural characterization (powder X-ray diffraction and X-ray photoelectron spectroscopy) of the Fe₃O₄@Ag hybrid materials reveal doping of Ag⁰ in O_h Fe²⁺ substitutional vacancies of the Fe₃O₄ host and Ag⁰ nanoparticle growth on and embedded deep within (>400 nm, Ar⁺ sputtering) the octahedra. These hybrid materials activate CO₂ and perform C­(sp)–H and C­(sp³)–Cl bond scission of alkyne substrates to selectively produce lactone heterocycles in up to 85% yield. Control reactions delineate two distinct pathways for the mechanism involving the complementarity of interfacial sites where alkyne activation occurs at Fe–O sites and CO₂ incorporation is predominately managed by Ag⁰. The recyclability of the Fe₃O₄@Ag-40B hybrid catalyst is demonstrated over five cycles and it shows the structural integrity of the octahedra, but a gradual drop in yield of the product from 85 to 45% due to slow depletion of surface Ag NPs is observed. Together, these results illustrate a rare understanding of the cooperative synergy and mechanism of multimetallic nanocatalyst interfaces for multiple substrate reactivity.