Green synthesis of a palladium-polyaniline nanocomposite for green Suzuki-Miyaura coupling reactions

A palladium-polyaniline (Pd-PANI) nanocomposite was successfully synthesized using a one-pot green synthetic procedure in water by the reaction between aniline hydrochloride and potassium hexachloropalladate. Strong interaction between PANI and Pd was clearly evident in the UV-visible and Fourier transform infrared (FTIR) spectrum of the nanocomposite. Powder X-ray diffraction (XRD) patterns revealed the presence of Pd(0) in the nanocomposite with a fcc crystal structure. Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) imaging showed that the Pd-PANI nanocomposite has spherical morphology with an average particle size of 175 +/- 42 nm. High resolution TEM imaging and energy dispersive X-ray (EDX) spectroscopy studies revealed that very small nanoparticles of Pd (3.1 +/- 0.9 nm) were found dispersed throughout the PANI matrix. X-ray photoelectron spectroscopy (XPS) revealed the presence of Pd(0) in the nanocomposite. The catalytic behavior of the Pd-PANI nanocomposite was studied for Suzuki-Miyaura coupling reactions in the presence of different bases in both organic and aqueous media. The results revealed that the Suzuki-Miyaura reaction proceeds much faster in water than in toluene. The excellent catalytic activity of the nanocomposite resulted in 86 and 91% yield in water and toluene respectively, when potassium carbonate was used as the base.