Real-Time SERS Insights into Plasmon-Mediated Suzuki-Type Cross-Coupling on Bimetallic Ag-Based Substrates

Suzuki–Miyaura coupling is a widely adopted method for constructing biaryl frameworks, yet its conventional dependence on soluble organopalladium complexes or costly palladium (Pd) nanoparticles, coupled with high temperatures and long reaction times, limits its sustainability. In this work, we introduce a Pd-free approach using bimetallic Ag–Cu and Ag–Co plasmonic microflowers (MFs) to drive the Suzuki–Miyaura coupling of halothiophenols (4-XTP, X = Br, Cl, F) at room temperature under visible light. These bimetallic structures are fabricated via a simple, surfactant-free thermolysis route that yields clean, highly branched microflower-like morphology with abundant plasmonic ‘hotspots’. They exhibit robustness, remaining nonagglomerated and catalytically active over multiple cycles, which makes them practical platforms for real-time mechanistic studies. By leveraging the strong SERS activity of these substrates, we dynamically monitored bond activation and coupling events in real time, revealing a heterogeneous, hot-carrier-driven mechanism distinct from classical Pd-based catalysis. Alloying silver (Ag) with Cu enhances hot-electron transfer and stabilizes Ag against oxidation, enabling faster C–Cl activation, while Co, though intrinsically nonplasmonic, introduces redox-active sites that accumulate hot holes and augment the challenging C–F and C–B activations through synergistic reactive oxygen species (ROS) formation. Wavelength-dependent studies further show that reaction rates increase with photon energy from 632.8 to 457 nm, highlighting that only at shorter excitation wavelengths do the hot carriers attain sufficient energy to overcome the higher activation barriers for C–Cl and especially C–F scission. Together, these results provide direct mechanistic evidence that compositional tuning of bimetallic plasmonic substrates, coupled with careful selection of excitation wavelength, can be used to orchestrate multistep bond activations under mild conditions and guide the rational design of next-generation multifunctional catalysts.