Single-Particle Spectro-Catalytic Platform Enabling High-Efficiency Synthesis and Mechanistic Tracking of Cu-Driven...

Conventional benzimidazole synthesis faces several challenges, including harsh reaction conditions, the formation of aldehyde-related byproducts, and a lack of comprehensive mechanistic insights. To address these limitations, we engineered a bifunctional Cu/ZnO catalyst that facilitates high-efficiency synthesis of benzimidazole while enabling in situ mechanistic monitoring. The spherical ZnO superstructure enhances Lewis acidity (91.2 µmol g^-1) optimizing the adsorption of o-arylenediamines. Concurrently, Cu nanoparticles (NPs) promote charge separation, evidenced by a 6-fold increase in photocurrent and a carrier lifetime of 1.57 ns, while selectively cleaving the α-C─H bonds of alcohols to generate ^•CH(R₂)OH radicals such as ^•CH(CH₃)OH. Notably, this radical-driven pathway circumvents the formation of aldehyde intermediates, achieving a record 2-methylbenzimidazole (2MBZ) productivity of 3.28 mmol g^-1 h^-1 with a yield of 98% yield and over 95% stability across five cycles. Furthermore, integrated surface-enhanced Raman scattering (SERS) spectroscopy provides detailed insights at the single-particle level, directly capturing transient species, such as radical intermediates (1170 cm^-1) and Schiff bases (1568 cm^-1). These findings elucidate the dual role of Cu NPs in both radical adsorption/cross-coupling and Lewis acid-mediated stabilization of intermediates. Thus, this work establishes a synergistic strategy that combines high-efficiency photocatalysis with in situ mechanistic tracking for sustainable heterocycle synthesis.