The Palladium Slow-Release Pre-Catalysts and Nanoparticles in the Phosphine-Free Mizoroki-Heck and Suzuki-Miyaura Reactions

The Mizoroki-Heck reaction of electron-rich aryl iodides was studied using a phosphine-free catalytic system with a broad range of pre-catalysts of varied stability and structure based on organoselenium chelators. The application of the mercury test by observing the response of the catalytic systems studied not only to the addition, but also to the withdrawal of Hg allowed us to establish a critical role of nanoparticles in the operation of the phosphine-free catalytic systems. A three-stage mechanistic scheme involving a slow stage served by mononuclear Pd species, and the main fast stage served by Pd nanoparticles, and terminated by the nanoparticle decay is proposed as a general mechanistic paradigm for the phosphine-free Mizoroki-Heck and the related Suzuki-Miyaura reactions.