Making C-C bond with gold catalysts: A theoretical study of the influence of gold particle size on the dissociation of the C-X bond in aryl halides

The adsorption and activation of iodo-, bromo-, and chlorobenzene over gold catalysts of different size, including an extended Au(111) surface; three-dimensional Au38 and Au13 nanoparticles; and planar Au7, Au6, and Au3 clusters has been systematically investigated by means of periodic density functional theory calculations. Several adsorption modes have been explored for each molecule, and the relative stability of such modes and the degree of C−X or C−C bond activation has been rationalized in terms of their molecular orbital distribution. Analysis of the electronic properties of the gold catalyst models allows the explanation of the influence of particle size on adsorption and activation energies in the subnanometer regime, while inclusion of dispersion interaction corrections becomes crucial for describing the reactivity of larger nanoparticles.Financial support from the Spanish Science and Innovation Ministry (Consolider Ingenio 2010-MULTICAT CSD2009-00050, Subprograma de apoyo a Centros y Universidades de Excelencia Severo Ochoa SEV 2012 0267, MAT2011-28009 projects) is acknowledged. Red Espanola de Supercomputacion (RES) and Centre de Calcul de la Universitat de Valencia are gratefully acknowledged for computational facilities and technical assistance. T.L.-A. thanks ITQ for a contract.Boronat Zaragoza, M.; López Auséns, JT.; Corma Canós, A. (2014). Making C-C bond with gold catalysts: A theoretical study of the influence of gold particle size on the dissociation of the C-X bond in aryl halides. Journal of Physical Chemistry C. 118(17):9018-9029. https://doi.org/10.1021/jp500806wS901890291181

Gold Redox Catalytic Cycles for the Oxidative Coupling of Alkynes

[EN] Au(I)/Au(III) catalytic cycles are catalytically competent to perform the oxidative coupling of alkynes in the homogeneous phase at room temperature and without any protecting atmosphere. Selectfluor as oxidant, wet acetonitrile as solvent, and sodium carbonate as base are the reagents of choice. Both aromatic and alkyl alkynes can be coupled, and mechanistic studies reveal that at least two gold species having different oxidation states are implicated in the key step of the coupling.A.L.-P. thanks CSIC for a contract. Financial support by Consolider-Ingenio 2010 (proyecto MULTICAT), PLE2009 project from MCIINN, and King Saud University is also acknowledged.Leyva Perez, A.; Doménech, A.; Al-Resayes, SI.; Corma Canós, A. (2011). Gold Redox Catalytic Cycles for the Oxidative Coupling of Alkynes. ACS Catalysis. 2(1):121-126. doi:10.1021/cs200532cS1211262

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

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

Making C-C bonds with gold: identification of selective gold sites for homo- and cross-coupling reactions between iodobenzene and alkynes

The nature of the active sites involved in the gold catalyzed Sonogashira cross-coupling reaction between iodobenzene and phenylacetylene, and in the competitive homocoupling reactions, has been investigated by means of DFT calculations, kinetic measurements, and synthesis of catalysts with different gold surface species. Several catalyst models have been theoretically investigated to simulate gold nanoparticles of different size either isolated, supported on inert materials, or supported on CeO2. The mechanistic studies show that 113 dissociation occurs on low coordinated Au-0 atoms present in small gold nanoparticles, either isolated or supported, while PA is preferentially adsorbed and activated on Au delta+ species existing at the metal-support interface. When this occurs, the activation energy of the rate-determining step of the Sonogashira reaction, which has been found experimentally to be the bimolecular coupling, is minimized The product distribution obtained with Au/CeO2 catalysts containing different ratios of Au-0/Au delta+ sites confirms the positive role played by cationic gold in the Sonogashira cross coupling reaction. Importantly, only metallic Au atoms present in gold nanoparticles are required to perform the homocoupling of iodobenzene.Financial support by the Spanish MICINN (CONSOLIDER Ingenio 2010-MULTICAT) and Generalitat Valenciana (PROMETEO project 2088/130) is gratefully acknowledged. R.J. and D.C. thank the Spanish MICINN for postgraduate scolarships, and S.L. thanks ITQ for a postdoctoral fellowship. We thank Red Espanola de Supercomputacion (RES) and Centre de Calcul de la Universitat de Valencia for computational resources and technical assistance.Boronat Zaragoza, M.; Cómbita Merchán, DF.; Concepción Heydorn, P.; Corma Canós, A.; García Gómez, H.; Juárez Marín, R.; Laursen ., SO.... (2012). Making C-C bonds with gold: identification of selective gold sites for homo- and cross-coupling reactions between iodobenzene and alkynes. Journal of Physical Chemistry C. 116(47):24855-24867. https://doi.org/10.1021/jp3071585S24855248671164