Ever since homogeneous gold was recognized as an active catalyst, the investigation of its use in homogeneous catalysis has undergone explosive development. Numerous new reactions have been discovered using homogeneous gold, the majority of which are based on the propensity of gold to function as a soft and carbophilic Lewis acid on the activation of carbon-carbon π-bonds, thus allowing nucleophilic attack on activated multiple bonds. However, most of these gold-catalyzed reactions suffer from high catalyst loading or catalyst decay problems. In addition, homogeneous gold catalysts cannot be recycled. These disadvantages limit their application in large-scale synthesis and cause a serious waste of this precious metal. A solution to these problems is to use a recyclable heterogeneous gold catalyst. Supported gold nanoparticles that are mainly composed of metallic gold clusters contain small amounts of cationic gold species. We found that these support-stabilized cationic gold species have similar efficiency as homogeneous gold catalysts. We developed an efficient alkyne hydration catalyzed by gold nanoparticles (Au/TiO2) under basic conditions. Our methodology creatively solved the incompatibility problem of acid-sensitive functional groups with conventional acid conditions needed for alkyne hydration. In addition to alkyne hydration, both weak-basic anilines and basic aliphatic amines are also good nucleophiles for activated alkynes; this allowed the easy construction of C-N bond under the mediation of Au/TiO2. The Au-TiO2 catalysts are easily handled and fairly air-stable. they can be recycled easily by simple filtration and work well in flow reactors with only slight loss of catalytic activity after repeated use.

Gold nanoparticle-catalyzed alkyne activation: Hydration under basic conditions and hydroamination

251st National Meeting (2016)

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