Growth of Au-Pd₂Sn Nanorods via Galvanic Replacement and Their Catalytic Performance on Hydrogenation and Sonogashira Coupling Reactions

Colloidal Pd₂Sn and Au-Pd₂Sn nanorods (NRs) with tuned size were produced by the reduction of Pd and Sn salts in the presence of size- and shape-controlling agents and the posterior growth of Au tips through a galvanic replacement reaction. Pd₂Sn and Au-Pd₂Sn NRs exhibited high catalytic activity toward quasi-homogeneous hydrogenation of alkenes (styrene and 1-octene) and alkynes (phenylacetylene and 1-octyne) in dichloromethane. Au-Pd₂Sn NRs showed higher activity than Pd₂Sn for 1-octene, 1-octyne, and phenylacetylene. In Au-Pd₂Sn heterostructures, X-ray photoelectron spectroscopy evidenced an electron donation from the Pd₂Sn NR to the Au tips. Such heterostructures showed distinct catalytic behavior in the hydrogenation of compounds containing a triple bond such as tolan. This can be explained by the aurophilicity of triple bonds. To further study this effect, Pd₂Sn and Au-Pd₂Sn NRs were also tested in the Sonogashira coupling reaction between iodobenzene and phenylacetylene in N, N-dimethylformamide. At low concentration, this reaction provided the expected product, tolan. However, at high concentration, more reduced products such as stilbene and 1,2-diphenylethane were also obtained, even without the addition of H₂. A mechanism for this unexpected reduction is proposed.