Robert S. Shue

Reactions of aromatics and olefins catalyzed by homogeneous palladium(II) compounds under oxygen

Abstract It has been found that the use of mild oxygen pressure in conjunction with homogeneous palladium(II) compounds in appropriate solvents allows olefin arylation and the oxidative coupling of olefins to proceed catalytically with respect to the metal. This is in contrast to the stringent conditions involving reoxidation catalysts, co-solvents and other adjuvants which were previously necessary to avoid quantitative reduction of palladium(II) to palladium(0) by reactions of this type. The scope and limitations of the reaction under these conditions are discussed. The new conditions allow olefin arylation to proceed normally with certain olefins, such as ethylene, which give mainly side reactions under previous conditions. Using the phenylation of styrene as a model reaction, the effects on the reaction of various parameters, such as catalyst ligands, oxygen pressure and catalyst level, were studied. Below a critical level of oxygen pressure, some catalyst reduction occurs even though catalytic yields of products may be obtained. Above this level, however, no catalyst reduction occurs and the reaction is essentially zero order with respect to oxygen.