Clusters Couple Chloroarenes

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Science  04 Jan 2013:
Vol. 339, Issue 6115, pp. 11
DOI: 10.1126/science.339.6115.11-b

In the classic Ullmann coupling reaction reported more than a century ago, iodine-substituted aromatic rings were coupled at high temperatures by using copper as a reducing agent to form a carbon-carbon bond. Further work extended this coupling reaction to more conventional chloroarenes by using coreductants and precious-metal catalysts, but reaction temperatures still tended to be high. Dhital et al. now show that a wide variety of chloroarenes can be coupled at ambient temperatures (25° to 45°C). The reactions proceeded under basic conditions (in a mixed organic-aqueous solvent) in the presence of gold-palladium nanocluster catalysts. Neither pure gold nor pure palladium clusters could catalyze the reaction, indicating that alloying of the metals was critical for reactivity. Density functional theory calculations indicated that the critical difference for the alloy clusters is that they favor activation of the carbon-chlorine bond through the dissociative adsorption of the arene chlorides.

J. Am. Chem. Soc. 10.1021/ja309606k (2012).

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