| 1. |
- Johansson, Niclas, et al.
(author)
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Sonogashira cross-coupling over Au(1 1 1): from UHV to ambient pressure
- 2017
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In: Journal of Physics: Condensed Matter. - 1361-648X. ; 29:44
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Journal article (peer-reviewed)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.
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| 2. |
- Majeed, Maitham H., et al.
(author)
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Polymer-Supported Palladium(II) Carbene Complexes : Catalytic Activity, Recyclability, and Selectivity in C-H Acetoxylation of Arenes
- 2017
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In: Chemistry - A European Journal. - : Wiley. - 0947-6539. ; 23:35, s. 8457-8465
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Journal article (peer-reviewed)abstract
- Heterogeneous catalysts for selective oxidation of C-H bonds were synthesized by co-polymerization of new N-heterocyclic carbene-palladium(II) (NHC-PdII) monomers with divinylbenzene. The polymer-supported NHC-PdII-catalysed undirected C-H acetoxylation of simple and methylated arenes as well as polyarenes, with similar or superior efficiency compared to their homogeneous analogues. In particular, the regioselectivity has been improved in the acetoxylation of biphenyl and naphthalene compared to the best homogeneous catalysts. The new polymer-supported catalysts maintain the original oxidation state of PdII after repeated catalytic reactions, and exhibit no significant leaching of palladium. In addition, the new catalysts have been successfully recovered and reused without loss of activity over several cycles of reactions.
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