Oxidized Charcoal-Supported Thiol-Protected Palladium Nanoparticles for Cross Dehydrogenative Coupling of Heteroarenes

This report describes the synthesis of thiol-protected Pd nanoparticles (NPs) (Pd-MUA) (MUA = 11-mercaptoundecanoic acid) supported on oxidized charcoal (OC-Pd-MUA) at room temperature. The Pd-MUA NPs and OC-Pd-MUA nanocomposites (NCs) were characterized with Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDX), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) techniques. The size distribution curve revealed that the diameter of the nanoparticles was in the range of ∼8–12 nm, and the surface area of the NCs was found to be 138.449 m²/g. The as-prepared OC-Pd-MUA NCs were used as a catalyst for the cross dehydrogenative coupling (CDC) of two different heteroarenes. Remarkably, the catalyst was found to be very efficient in activating various heteroarenes under mild reaction conditions. Most importantly, no homocoupled or other byproducts were observed during the heterocoupling reactions. Moreover, the catalyst can be potentially used for the homocoupling reaction of various heteroarenes. It is noteworthy that only 0.22 mol % catalyst loading was required to activate a broad substrate scope with large functional group tolerance. Notwithstanding, the efficacy of the catalyst was found to be retained even after six reaction cycles. The reusability and hot filtration tests validated the heterogeneous nature of the catalysis. In addition, the experimental and computational studies collectively suggested that thiophene derivatives react to produce energetically stable products compared with other heteroarenes during the reaction.