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This paper reports the development of a new family of highly active Pd nanoparticle catalysts supported on partially reduced graphene oxide nanosheets for carbon–carbon cross-coupling reactions. We report, for the first time, the synthesis of Pd nanoparticle catalysts supported on partially reduced graphene nanosheets (Pd/PRGO) by pulsed laser irradiation of aqueous solutions of graphene oxide and palladium ions without the use of chemical reducing or capping agents. The redox reactions initiated by the photoexcitation of GO using two 532 nm photons in different reducing environments of appropriate protic solvents (water, methanol, and ethanol) result in the formation of Pd nanoparticles with different sizes supported on the PRGO nanosheets. The laser irradiation process leads to the formation of multiple defect sites on the surface of the PRGO nanosheets which provide an excellent environment for anchoring the Pd nanoparticles, thus impeding the particles’ migration and increasing the catalyst–support interaction. This consequently contributes to the enhanced catalytic performance and recyclability of the catalyst. The Pd/PRGO catalyst generated in water demonstrates excellent catalytic activity for Suzuki, Heck, and Sonogashira cross coupling reactions, with good recyclability for Suzuki coupling with a turn over number (TON) of 7800 and a remarkable turnover frequency (TOF) of 230,000 h–1 at 120 °C under microwave heating. The results indicate that the defect sites generated on the PRGO nanosheets by the laser photochemical process play a major role in imparting the exceptional catalytic properties to these catalysts.

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Palladium nanoparticles supported on single-or multi-walled carbon nanotubes (Pd/SWCNT and Pd/ MWCNT) were prepared by a rapid, solventless method that does not require reducing agents or electric current. The method involves a straightforward process using dry mixing of a precursor Pd salt (e.g., palladium acetate) with carbon nanotubes at ambient temperature by ball-milling (mechanochemical route) or with subsequent annealing at 300 C (thermal route) in an inert atmosphere. The Pd/MWCNT sample with Pd nanoparticle size of 1-3 nm and uniform dispersion prepared by mechanochemical ballmilling at room temperature [designated as (Pd/MWCNT) M ] displayed remarkable catalytic activity towards Suzuki cross coupling reactions with a high turn over number (TON) of 7250 and turn over frequency (TOF) of 217 500 h À1 . These nanoparticles were characterized by a variety of techniques including transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Additionally, the (Pd/MWCNT) M sample was successfully employed in Suzuki cross coupling reactions with a wide variety of functionalized substrates.

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Conjugated polymers have emerged over the past several decades as key components for a range of applications, including semiconductors, molecular wires, sensors, light switchable transistors and OLEDs. Nevertheless, the construction of many such polymers, especially highly substituted variants, typically involves a multistep synthesis. This can limit the ability to both access and tune polymer structures for desired properties. Here we show an alternative approach to synthesize conjugated materials: a metal-catalysed multicomponent polymerization. This reaction assembles multiple monomer units into a new polymer containing reactive 1,3-dipoles, which can be modified using cycloaddition reactions. In addition to the synthetic ease of this approach, its modularity allows easy adaptation to incorporate a range of desired substituents, all via one-pot reactions.

N-Chelation-directed C-H activation reactions that utilize the Pd(II)/Pd(IV) catalytic cycle have been previously reported. To date, these reactions employ only homogeneous palladium catalysts. The first use of a solid-supported Pd(II) catalyst [Pd(II) nanoparticles on multiwalled carbon nanotubes, Pd(II)/MWCNT] to carry out N-chelation-directed C-H to C-O, C-Cl, and C-Br transformations is reported. The results presented demonstrate that the solid-supported Pd(II)/MWCNT catalyst can effectively catalyze C-H activation reactions using the Pd(II)/Pd(IV) catalytic cycle.

A palladium-catalyzed one-step synthesis of imidazoles from imines and acid chlorides is described. A plausible mechanism for this multicomponent reaction is provided, which explains the selective incorporation of two different imines into the final product with perfect regiocontrol. Overall, this catalytic process provides a modular method to prepare imidazoles directly from building blocks that are all either commercially available or readily generated.