Effects of doping in 25-atom bimetallic nanocluster catalysts for carbon-carbon coupling reaction of iodoanisole and phenylacetylene

We here report the catalytic effects of foreign atoms (Cu, Ag, and Pt) doped into well-defined 25-gold-atom nanoclusters. Using the carbon-carbon coupling reaction of p-iodoanisole and phenylacetylene as a model reaction, the gold-based bimetallic MxAu25-x(SR)(18) (-SR=-SCH2CH2Ph) nanoclusters (supported on titania) were found to exhibit distinct effects on the conversion of p-iodoanisole as well as the selectivity for the Sonogashira cross-coupling product, 1-methoxy-4-(2-phenylethynyl) benzene). Compared to Au-25(SR)(18), the centrally doped Pt1Au24(SR)(18) causes a drop in catalytic activity but with the selectivity retained, while the AgxAu25-x(SR)(18) nanoclusters gave an overall performance comparable to Au-25(SR)(18). Interestingly, CuxAu25-x(SR)(18) nanoclusters prefer the Ullmann homo-coupling pathway and give rise to product 4,4'dimethoxy- 1,1'-biphenyl, which is in opposite to the other three nanocluster catalysts. Our overall conclusion is that the conversion of p-iodoanisole is largely affected by the electronic effect in the bimetallic nanoclusters' 13-atom core (i.e., Pt1Au12, CuxAu13-x, and Au-13, with the exception of Ag doping), and that the selectivity is primarily determined by the type of atoms on the MxAu12-x shell (M=Ag, Cu, and Au) in the nanocluster catalysts.