Efficient Catalytic System for Synthesis of trans-Stilbene from Diphenylacetylene Using Rh-Based Intermetallic Compounds

A series of Rh-based intermetallic compounds supported on silica (RhmM′n/SiO2, M′ = Bi, Ge, In, Sb, and Sn) were prepared and tested as catalysts for trans-stilbene (trans-ST) synthesis from diphenylacetylene (DPA) in H2 atmosphere. Rh2Sb/SiO2 exhibited high catalytic activity in the semihydrogenation of DPA to cis-ST and subsequent isomerization to trans-ST, with a smaller capability of overhydrogenation to diphenylacetylene (DPE) than Rh/SiO2, affording a moderate yield of trans-ST (58%) after complete conversion of DPA. RhSb/SiO2 possesses a unique hydrogenation property capable of half-hydrogenation but minimal overhydrogenation, which enables highly selective isomerization of cis-ST to trans-ST. A tandem catalytic system using RhSb/SiO2 and Pd3Bi/SiO2 afforded 88% yield of trans-ST. These results are the first examples of the effective synthesis of trans-ST from DPA using heterogeneous metallic catalysts.