Dendritic Molecular Template Mediates and Directs Self-Assembly of Uniform Gold Nanoclusters to One-Pot Afford 3D-Supported Active Catalysts

Uniform gold nanoclusters (AuNCs) are hardly available unless through abundant strong ligands (at the cost of low catalytic activity and narrow catalytic spectrum) or through well-defined (but expensive) templates, and it appears a tougher challenge for direct preparing supported and uniform AuNCs. Here, we show that with an amphiphilic and dendritic molecular template in hand, highly catalytically active, uniform, and supported AuNCs are one-pot achievable. Branched polyethylenimine (PEI) is modified with a few thioether groups and alkylated with hydrophobic acetyls and polystyrene chains to afford reverse micelle-like dendritic polymers. The structurally optimized dendritic polymer can act as a surfactant to mediate very stable water-in-oil high internal phase emulsion (HIPE) within a wide pH spectrum. Moreover, the dendritic polymer switches into the unimolecular state along the interface of the HIPE when pH is below 6, which is critical to the formation of uniform AuNCs. Experimentally, upon the transformation of HIPE into an open-cellular polyHIPE, the gold ions are simultaneously transformed into AuNCs. Direct preparation of the supported and uniform AuNCs (1.8 ± 0.2 nm) are feasible because the dendritic polymer can simultaneously act as a surfactant, a polymer ligand, and a unimolecular template. Meanwhile, the trace thioether groups in the PEI core reduce the size of AuNCs by enhancing nucleation of AuNCs since in the absence of thioether groups, larger particles are obtained. The supported AuNCs are catalytically active because they are stabilized by weak coligands. For the model reaction of the catalyzed reduction of 4-nitrophenol, the catalyst shows a turnover frequency of 112.5 h–1, which is very high. The catalyst is durable and well recyclable.