Preparation of magnetically recoverable carbon nanotube-supported Pd(II) catalyst

Multi-walled carbon nanotubes were filled or externally decorated with iron oxide nanoparticles to make them magnetically-recoverable. In the first case, the external surface was treated to be free of defects and oxygenated groups to favor internalization. A thermal decomposition route was followed in the second case. The formed nanoparticles were characterized and shown to consist in magnetite and/or maghemite. Moreover, when placed on the external surface of carbon nanotubes, they remained small and well-dispersed, leaving high proportion of free carbon surface for further functionalization. The intact sp(2) carbon atoms were subsequently attacked by means of xanthate radical chemistry, followed by post-functionalization to graft a dipyridylamine ligand on the surface of both solids and pristine carbon nanotubes for comparison. Solids at each step of the syntheses were characterized by X-ray photoelectron spectroscopy (XPS). Palladium coordination onto the surface ligand was studied and the precursor [Pd(COD)Cl-2] complex gave the best results to afford CNT-supported molecular Pd(II) catalysts. XPS confirmed the + 2 oxidation state of palladium on the carbon surface. The so-prepared magnetically-recoverable catalysts were successfully used in Suzuki-Miyaura cross-coupling catalytic application.