Addition of a strong oxidizing agent to a gold-catalysed reaction results in a gold(III) intermediate that significantly broadens the scope of such catalysis
The homogeneous catalytic activity of gold complexes is usually only dependent on the reaction of gold(I) species in solution, and their reaction with electron-rich substrates such as allenes and alkynes. Other transition metals such as palladium and nickel often undergo changes in oxidation state during catalysis. Although this is far rarer for gold, it has been suggested that gold(III) intermediates are involved in several heterogeneous gold-catalysed process.
Now, Liming Zhang and co-workers from the University of Nevada, USA, have developed1 a new gold-catalysed oxidative cross-coupling reaction. In attempting to develop a gold catalysed fluorination, they chose Selectfluor — an electrophilic source of fluorine — but observed significant dimerization of their starting material as a side reaction. They attributed this to the oxidation of a key gold(I) intermediate and the formation of a gold(III) fluoro complex, and then attempted to intercept it with a suitable nucleophile. Adding a boronic acid to the reaction mixture worked, and resulted in a cross-coupled product — an α-arylenone.
The strategy combines the power of gold-catalysed activation of electron-rich substrates with the wealth of available knowledge on oxidative cross-coupling reactions, and should significantly expand the scope of products attainable using gold catalysis.
References
Zhang, G., Peng, Y, Cui, L. & Zhang, L. Gold-catalyzed homogeneous oxidative cross-coupling reactions. Angew. Chem. Int. Ed. 10.1002/anie.200900585 (2009).
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Davey, S. Going for gold(III). Nature Chem (2009). https://doi.org/10.1038/nchem.211
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DOI: https://doi.org/10.1038/nchem.211