Formation of dispersed palladium–nickel bimetallic nanoparticles in microemulsions: synthesis, characterization, and their use as efficient heterogeneous recyclable catalysts for the amination reactions of aryl chlorides under mild conditions
A simple method for preparing spherical palladium–nickel bimetallic nanoparticles with a molar ratio of 1.0 (Pd0.5–Ni0.5 B-NPs) has been adopted using a water-in-oil microemulsion system of water/aerosol-OT/isooctane at room temperature. The morphology, size, structure, and elemental composition of these particles as the superior catalyst were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive analysis using X-rays (EDAX), and X-ray fluorescence (XRF) analyses. The effects of the reaction parameters on the Buchwald–Hartwig amination reaction yield in the presence of these NPs as catalyst have been screened and the results are evaluated by using chlorobenzene and morpholine as a model reaction. Initially, differences in the catalytic properties of some synthesized NPs have been compared. In this context, Pd–Ni B-NPs with the molar ratio of 1 : 1 (Pd/Ni = 1) showed the highest catalytic activity for this reaction. The Pd0.5–Ni0.5 B-NPs are stable and the leaching of catalyst in solution is very low. Therefore, they has been employed as efficient catalysts in the C–N coupling reaction. Finally, a mechanism for an amination reaction on the Pd/Ni catalyst surface was proposed.