Sonogashira Coupling on an Extended Gold Surface in Vacuo: Reaction of Phenylacetylene with Iodobenzene on Au(111)

Abstract

Temperature-programmed reaction measurements supported by scanning tunneling microscopy have shown that phenylacetylene and iodobenzene react on smooth Au(111) under vacuum conditions to yield biphenyl and diphenyldiacetylene, the result of homocoupling of the reactant molecules. They also produce diphenylacetylene, the result of Sonogashira cross-coupling, prototypical of a class of reactions that are of paramount importance in synthetic organic chemistry and whose mechanism remains controversial. Roughened Au( 111) is completely inert toward all three reactions, indicating that the availability of crystallographically well-defined adsorption sites is crucially important. High-resolution X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy show that the reactants are initially present as intact, essentially flat-lying molecules and that the temperature threshold for Sonogashira coupling coincides with that for C-I bond scission in the iodobenzene reactant. The fractional-order kinetics and low temperature associated with desorption of the Sonogashira product suggest that the reaction occurs at the boundaries of islands of adsorbed reactants and that its appearance in the gas phase is rate-limited by the surface reaction. These findings demonstrate unambiguously and for the first time that this heterogeneous cross-coupling chemistry is an intrinsic property of extended, metallic pure gold surfaces: no other species, including solvent molecules, basic or charged (ionic) species are necessary to mediate the process.

Identity of the Active Site in Gold Nanoparticle-Catalyzed Sonogashira Coupling of Phenylacetylene and Iodobenzene

“…6 Consistent with this, the characteristic orange-brown color of the iodine co-product was observed in every case. Thus:…”

“…5 This view was also consistent with the pronounced metal particle size effects that were observed 5 and with the results of recent single crystal observations of the same reaction carried out on an extended Au(111) surface. 6 Scheme 1 Coupling reactions of iodobenzene and phenylacetylene to yield both the desired Sonogashira cross-coupling product diphenylacetylene (DPA) and the two homo-coupling side products diphenyldiacetylene and biphenyl.…”

Homo-coupling of terminal alkynes on a noble metal surface

“…These have been nicely exemplified by cyclodehydrogenation processes on Cu(111) for tailored nanographenes 19 , or site-specific linear alkane polymerization on an Au(110) facet 20 . A recent related report reveals the prominent role of a noble metal substrate in the catalytic course of a C À C Sonogashira coupling reaction elucidating its heterogenic nature 21 .…”

Electrochemical monitoring of the oxidative coupling of alkynes catalyzed by triphenylphosphine gold complexes

“…The formation of 1,4-diphenylbutadiyne as by-product in the cascade cyclizationoxidative alkynylation of allenoates with selectfluor catalyzed by gold complexes [13] as well as in the Sonogashira reaction catalyzed gold-supported nanoparticles [14][15][16][17][18][19] are recent examples for the use of gold-based catalyst. In a prior report, we have described the catalytic effect of a series of PPh 3 -Au(I) complexes on the oxidative homocoupling of terminal alkyl and aryl alkynes using selectfluor as oxidant and Na 2 CO 3 as base in non-dried acetonitrile [20].…”