Photocatalytic Pinacol C–C Coupling and Jet Fuel Precursor Production on ZnIn₂S₄ Nanosheets

Abstract

Visible light-driven C–C bond formation has attracted increasing attention recently, thanks to the advance in molecular photosensitizers and organometallic catalysts. Nevertheless, these homogeneous methodologies typically necessitate the utilization of noble metal-based (e.g., Ir, Ru, etc.) photosensitizers. In contrast, solid-state semiconductors represent an attractive alternative but remain less explored for C–C bond-forming reactions driven by visible-light irradiation. Herein, we report that photocatalytic pinacol C–C coupling of benzaldehyde to hydrobenzoin can be achieved on two-dimensional ZnIn2S4 nanosheets upon visible-light irradiation in the presence of a sacrificial electron donor (e.g., triethylamine). We further demonstrate that it is feasible to take advantage of both excited electrons and holes in irradiated ZnIn2S4 for C–C coupling reactions in the absence of any sacrificial reagent if benzyl alcohol is utilized as the starting substrate, maximizing the energy efficiency of photocatalysis and circumventing any byproducts. In this case, industrially important benzoin and deoxybenzoin are formed as the final products. More importantly, by judiciously tuning the photocatalytic conditions, we are able to produce either benzoin or deoxybenzoin with unprecedented high selectivity. The critical species during the photocatalytic process were systematically investigated with various scavengers. Finally, such a heterogeneous photocatalytic pinacol C–C coupling strategy was applied to produce a jet fuel precursor (e.g., hydrofuroin) from biomass-derived furanics (e.g., furfural and furfural alcohol), highlighting the promise of our approach in practical applications.