Synthesis of a Palladium(IV) Complex by Oxidative Addition of an Aryl Halide to Palladium(II) and Its Use as Precatalyst In a C-C Coupling Reaction

摘要

The recent award of the 2010 Nobel Prize in Chemistry to Heck, Negishi, and Suzuki for their studies on catalytic cross couplings has recognized the important role of palladium in organic synthesis. Their methods were later improved by the use of Herrmann's palladacycles as precatalysts. Most of both types of reactions involve a palladium(0)/palladium(II) catalytic cycle. Palladium(O) species are the precatalysts in the classical reactions or form in situ from the Pd~(II) precatalyst as a Pd~0 complex or as Pd nanoparticles. However, based on various experimental data, Pd~(II)/Pd~(IV) catalytic cycles have been proposed as an alternative. Some computational studies also support this proposal. However, since the oxidative addition of an aryl halide to a Pd~(II) complex and the existence of Pd~(IV) complexes in these catalytic processes have not yet been conclusively demonstrated, the Pd~(II)/Pd~(IV) catalytic cycle has become one of the most intriguing open problems in catalysis. Herein, we discuss the first of these two topics.