Investigations into the Stability of Tethered Palladium(II) Pincer Complexes during Heck Catalysis

A variety of palladated PCP pincer complexes are covalently tethered onto polymeric and silica supports via either amide or ether linkages and are evaluated in the Heck reaction of iodobenzene and <i>n</i>-butyl acrylate. The decomposition under reaction conditions of all complexes studied is established through poisoning and kinetic studies. Furthermore, the initial steps of the decomposition pathway of PCP as well as SCS pincer Pd(II) complexes are proposed and validated using in situ NMR, mass spectroscopy, and XAS as well as computational methods. These findings together with our previous reports strongly suggest that all Pd(II) pincer complexes are simply precatalysts during the Heck reaction that decompose to form catalytically active Pd(0) species.