Bulky Ligands Induce Rich Uncoordinated Sites for Boosting Metal Nanocluster Catalysis

The catalytic activity of ligand-protected metal nanoclusters is often hindered by the blocking effect of surface ligands, necessitating the creation of more uncoordinated sites to enhance their performance. In this work, we report a strategy for boosting the catalysis of fully ligand-protected silver nanoclusters by anchoring uncoordinated copper sites. By employing a bulky ligand, 2,4,6-triisopropylbenzenethiol, and a copper-functionalized reducing agent, a cluster denoted as Ag14Cu7(PPh3)6(SR)6 (Ag14Cu7, RSH is 2,4,6-triisopropylbenzenethiol) has been prepared. The structure of Ag14Cu7 closely resembles that of the previously reported Ag14(SPh(CF3)2)12(PPh3)4(DMF)4 (Ag14), whose geometric structure describes the addition of seven Cu atoms onto the Ag14 moiety, one at the center and another six on the surface. To our surprise, the presence of extra uncoordinated copper sites on the surface significantly enhances the catalytic activity of Ag14Cu7 in hydrogenation reactions. This work not only reports a model system to shed light on the significance of surface uncoordinated metal sites in cluster catalysis but also offers an effective strategy utilizing bulky ligands and functionalized reducing agents to generate additional uncoordinated sites on the surface of metal nanocluster catalysts.