Sonogashira cross-coupling over Au(111): from UHV to ambient pressure

We have studied the reaction of phenylacetylene (PA) with chloro-, bromo-, and iodobenzene on the Au(1 1 1) surface as a model system for the gold-catalysed Sonogashira cross-coupling. Both ultrahigh vacuum-based and ambient pressure x-ray photoelectron spectroscopy show that iodo-and chlorobenzene (IB and CB) undergo the cross-coupling reaction towards diphenylacetylene. Bromobenzene (BB), in contrast, does not react in the UHV experiments. Further, at ambient pressure signs are found for poisoning of the Au(1 1 1) surface by a carbon species formed in the reaction. The understanding obtained in the reaction experiments are based on a thorough investigation of the adsorption of PA, IB, CB, and BB on the Au(1 1 1) surface by soft x-ray absorption spectroscopy and temperature-dependent x-ray photoelectron spectroscopy. In particular, the experiments provide the orientation of the intact adsorbates with respect to the surfaces at liquid nitrogen temperature. Dissociation in the temperature regime between -80 and -15 degrees C is observed for iodo-and chlorobenzene, but not for BB, in agreement with that only IB and CB, but not BB, react with PA to form diphenylacetylene. The difference is tentatively attributed to a difference in surface orientation of the different halobenzenes.