Sonogashira cross-coupling reactions catalysed by copper-free palladium zeolites

A heterogeneous copper-free [Pd(NH3)(4)](2+) / (NH4)Y catalyst was employed to achieve the heterogeneous Sonogashira reaction of aryl halides with terminal alkynes. Several reaction parameters like solvent, base and temperature were evaluated. When optimised, the coupling reaction of bromobenzene with phenylacetylene gave a 45% yield of diphenylacetylene within 3 h using only 1 mol % Pd. This catalyst was successfully applied to the coupling reaction of a range of aryl iodides and bromides: aryl iodides and activated aryl bromides gave almost quantitative yields and non-activated aryl bromides led to reasonable yields (20% to 45%). This heterogeneous [Pd(NH3)(4)](2+)/(NH4)Y catalyst was shown to be efficient, stable towards leaching and recyclable for the copper-free Sonogashira reaction.