Reversible Control of Chemoselectivity in Au38(SR)24 Nanocluster-Catalyzed Transfer Hydrogenation of Nitrobenzaldehyde Derivatives.

Chemoselective hydrogenation of nitrobenzaldehyde derivatives is one of the important catalytic processes being studied in hydrogenation catalysis. In this work, we report for the first time the catalytic reaction over atomically precise gold nanocluster catalysts (Au25, Au38, Au52, and Au144) using potassium formate as the hydrogen source. A complete selectivity for hydrogenation of the aldehyde group, instead of the nitro group, is obtained. A distinct dependence on the size of nanocluster catalysts is also observed, in which the Au38(SCH2CH2Ph)24 gives rise to the highest catalytic activity. The catalyst also shows good versatility and recyclability. Interestingly, the ligand-off nanocluster changes its catalytic selectivity to the nitro hydrogenation, which is in contrast with the ligand-on catalyst. In addition, the selectivity can be restored by treating the ligand-off nanocluster catalyst with thiol. This reversible control of chemoselectivity is remarkable and may stimulate future work on the exploitation of such nanoclusters for hydrogenation catalysis with control over selectivity.