Sonogashira cross-coupling over Au(1 1 1): from UHV to ambient pressure

Abstract

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 °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.

Gold‐Catalyzed Cross‐Coupling Reactions: An Overview of Design Strategies, Mechanistic Studies, and Applications

“…Te mperature-programmed reaction (TPR) studies suggested that the temperature at whichS onogashira coupling occurs coincides with the temperature at which CÀIb ond scission of iodobenzene occurs over the Au(111)s urface (Scheme 75). [382] However,b romobenzene did not undergo the crosscoupling reaction. [376,380] Unlike the Au(111)s urface, the clean, smoothed Au(1 00)s urface showed lower reactivity toward CÀCc oupling than the roughened surface.…”

“…[381] Av ery recent experimental study Schnadt et al found that both chlorobenzenea nd iodobenzene underwent Sonogashira coupling with phenylacetyleneo ver Au(111)s urfaces. [382] However,b romobenzene did not undergo the crosscoupling reaction.…”

Spiers Memorial Lecture: prospects for photoelectron spectroscopy

“…As an example, a recent study of the Sonogashira cross-coupling reaction (a C-C bond-formation reaction between iodo-or chlorobenzene and phenylacetylene to form diphenylacetylene) conrmed earlier UHV results that Au (111) catalyses the reaction at moderate temperature and pressure. 34 However, rapid inactivation due to the formation of a carbonaceous species was observed at higher temperature and pressure, 34 illustrating the importance of NAP-XPS in providing more industrially relevant conditions. Although, as we discuss in Section 2.7, it has recently become possible to carry out NAP-XPS at pressures of 1 bar and above of a few mbar, and there remain signicant challenges to solve in studying real catalytic reactions of large molecules.…”