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Buchwald-Hartwig amination is a cross-coupling reaction between aryl halides or pseudohalides and primary or secondary amines to produce aryl amines. The reaction has become a fundamental tool in organic synthesis for the formation of carbon-nitrogen bonds in a variety of biologically active molecules, natural products, pharmaceuticals, and material science. These reactions usually employ a palladium complex in homogeneous form along with a ligand to stabilize the metal center. In this regard, there are many disadvantages for using homogeneous catalysis including the potential contamination of the metal in the final product and lack of recyclability of the catalyst. Heterogeneous catalysis is an alternative attractive approach to construct carbon-nitrogen bonds in which the metal is fixed on variety of solid supports such as zeolites, polymers, mesoporous silica, and carbon materials. This would allow for ease of separation of the catalyst from the reaction and reusability for the subsequent runs. In this presentation, we will introduce the synthesis of amine-functionalized carbon nanotubes (CNTs) supported Pd nanoparticles (Pd/MWCNTs-NH2) via simple dry mixing of the corresponding palladium salts and amine-functionalized CNTs using the mechanical energy of a ball-mill mixer. The method is very straightforward and rapid and does not require any solvent or reducing agents, a feature that allows for large-scale preparation of these materials. The as-prepared catalyst demonstrated excellent catalytic activity for the Buchwald-Hartwig carbon–nitrogen cross-coupling reactions of variety of aryl halides and functionalized amines under microwave irradiation conditions and short reaction time. The Pd/MWCNTs-NH2 nanoparticles prepared by this simple, solventless, and inexpensive preparation provide a more direct, cost-efficient, and streamlined means to accomplish often-challenging Buchwald-Hartwig amination reactions. 

We have developed an efficient method to generate highly active nickel–palladium bimetallic nanoparticles supported on multi-walled carbon nanotubes (Ni–Pd/MWCNTs) by dry mixing of the nickel and palladium salts utilizing the mechanical energy of a ball-mill. These nanoparticles were successfully employed in Sonogashira cross-coupling reactions with a wide array of functionalized aryl halides and terminal alkynes under ligand and copper free conditions using a Monowave 50 heating reactor. Notably, the concentration of palladium can be lowered to a minimum amount of 0.81% and replaced by more abundant and less expensive nickel nanoparticles while effectively catalyzing the reaction. The remarkable reactivity of the Ni–Pd/MWCNTs catalyst toward Sonogashira cross-coupling reactions is attributed to the high degree of the dispersion of Ni–Pd nanoparticles with small particle size of 5–10 nm due to an efficient grinding method. The catalyst was easily removed from the reaction mixture by centrifugation and reused several times with minimal loss of catalytic activity. Furthermore, the concentration of catalyst in Sonogashira reactions can be reduced to a minimum amount of 0.01 mol% while still providing a high conversion of the Sonogashira product with a remarkable turnover number (TON) of 7200 and turnover frequency (TOF) of 21 600 h −1 . The catalyst was fully characterized by a variety of spectroscopic techniques including X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS).