Highly Dispersed Palladium-Polypyrrole Nanocomposites: In-Water Synthesis and Application for Catalytic Arylation of Heteroaromatics by Direct C-H Bond Activation

Pd@PPy hybrid catalytic materials are synthesized in water via redox polymerization reaction of pyrrole with [Pd(NH3)(4)Cl-2]. The nanocomposites formed are composed of highly dispersed palladium particles which are either zerovalent or easily reducible, and are embedded in spherical polypyrrole globules. A unique combination of high palladium dispersion (NP size: 2.4 nm) and elevated palladium content (35 wt%) is obtained. The components of these novel nanocomposites are characterized by means of FTIR, XPS, XRD, SEM, and TEM microscopy techniques. The process of formation in solution is also monitored using UV-visible and DLS techniques. The application of these novel hybrid nanomaterials in the palladium-catalyzed direct arylation of heteroaromatics is reported. High efficiency in C-C bond formation is obtained using these materials. Furans and thiophenes are arylated by using bromoarenes. Pd@PPy nanocomposites can efficiently couple n-butyl furan and n-butyl thiophene with bromobenzene and bromoquinoline, as well as with activated or deactivated electron-poor and electron-rich functionalized bromoarenes. Thus, a clean reaction process is developed that combines the absence of organic ligand in catalytic reactions and easy recovery of Pd@PPy nanocomposite via simple filtration. Preliminary kinetic and post-catalysis studies suggest a molecular or colloidal soluble active species. These very active species are efficiently delivered by the nanocomposites and susceptible to a surprisingly uniform back redeposition within the polypyrrole support.