Formation and propagation of well-defined Pd nanoparticles (PdNPs) during C–H bond functionalization of heteroarenes: are nanoparticles a moribund form of Pd or an active catalytic species?

Examination of a series of C–H bond functionalization reactions of heteroarenes (e.g., indole, benzoxazole, benzthiazole, benzimidazole and purine derivatives) mediated by Pd(OAc)2, a commonly used C–H bond functionalization catalyst, reveals that well-defined Pd nanoparticles (PdNPs) are rapidly formed under working catalyst conditions. The PdNPs can be characterized ex situ after entrapment in a polymer matrix (polyvinylpyrrolidinone, PVP). Independently synthesized Pd(PVP)NPs are catalytically competent species, exhibiting catalyst activity commensurate with Pd(OAc)2 in several C–H bond functionalization reactions. Across a range of reactions, Pd concentration is a common variable, which can be linked to the propagation of PdNPs under working catalytic conditions using polar solvents like DMF, DMSO and acetic acid.