Copper-free heterogeneous catalysts for the Sonogashira cross-coupling reaction: Preparation, characterisation, activity and applications for organic synthesis

Heterogeneous copper-free catalysts supported on microporous ([Pd(NH3)(4)](2+)/NaY) and mesoporous materials ([Pd]/SBA-15) have been prepared, characterised and evaluated in the Sonogashira coupling reaction of aryl halides with phenyl acetylene. Generally, these catalysts showed high activity and selectivity, somewhat comparable to that of homogeneous catalysts (i.e. {Pd[P(o-C6H4CH3)(2)(C6H4CH2)[OCOCH3]}(2) and PdCl2(PPh3)(2)). In addition, it was found that the catalyst based on the SBA-15 material (i.e. [Pd]/SBA-15), was particularly active when using large aryl halides such as bromonaphtalene and bromoanthacene, whereas, the heterogeneous catalyst based on microporous support (i.e. [Pd(NH3)(4)](2+)/NaY) was inactive. The recycling of various catalyst and X-ray diffraction and P-31 CP-MAS NMR studies of fresh and recycled catalyst are also briefly discussed. (c) 2005 Elsevier B.V All rights reserved.