Adsorption-Biased, Halide-Tuned Perovskite Photocatalysts for Aerobic Oxidation of Primary Alcohols to Benzimidazoles

Achieving productive aerobic oxidation of alcohols in the presence of more easily oxidized partners is a central challenge in photocatalytic synthesis. In particular, visible-light-driven routes from abundant primary alcohols to benzimidazoles are hampered by the inertness of linear aliphatic alcohols and the oxidative fragility of <i>o</i>-phenylenediamines (OPDs), which has forced previous methods to use the alcohol as the bulk solvent. Here we show that halide-tuned CsPbX₃ (X = Cl/Br/I) perovskite nanocrystals act as adsorption-biased, band-engineered photocatalysts for this transformation. By adjusting the halide composition, we prepare a toolbox of photocatalysts whose excited-state oxidation potentials are matched to different classes of primary alcohols: CsPbCl₃ under 405 nm irradiation efficiently oxidizes linear aliphatic alcohols, whereas CsPbClBr₂ under 455 nm light is optimal for benzylic alcohols. For challenging linear aliphatic alcohols, this oxidative dehydrogenative coupling operates with only ∼3 equiv of the alcohol (rather than solvent-level quantities), while benzylic alcohols are converted with only 2 equiv, in all cases using O₂ (1 atm) as the terminal oxidant under mild, noble-metal-free and heterogeneous conditions to furnish a broad range of 2-alkyl and 2-aryl benzimidazoles. Temperature-programmed desorption experiments and density functional theory (DFT) calculations indicate that primary alcohols bind much more strongly to the perovskite surface than OPDs, while photophysical and electrochemical studies map a two-step interfacial electron-transfer sequence: alcohol → perovskite(h⁺) → O₂. Together, these results demonstrate an adsorption-biased, halide-tunable perovskite platform for alcohol-favored aerobic oxidation and suggest a general design strategy for heterogeneous photoredox synthesis.