Palladium supported on structurally stable phenanthroline-based polymer nanotubes as a high-performance catalyst for the aqueous Suzuki–Miyaura coupling reaction

Abstract

Though the Suzuki–Miyaura coupling reaction has intrinsic advantages in organic synthesis, it is still a challenging task to develop a highly active and truly heterogeneous catalyst for the aqueous Suzuki–Miyaura coupling reaction (SMR). In this work, a series of phenanthroline-based polymers (PBPs; PBP1 to PBP8) were synthesized by a simple one-step AlCl₃-catalyzed Friedel–Crafts polymerization method. Systematic measurements of PBPs by N₂ adsorption–desorption isotherms, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) show that most of the PBPs have a nanosheet morphology, except PBP8 which has both one-dimensional nanotubular morphology and large surface area (745 m² g⁻¹). Benefitting from the porous nanotube morphology and the two N atoms contained in the phenanthroline unit of the polymer structure, polymer PBP8 shows adsorption effects and strong chelating stabilization on the Pd active metal (size, 2–5 nm). The Pd/PBP8 catalyst exhibits superior catalytic activity within 2 h (TOF value: 3077 h⁻¹) and reusability (7 cycles) in the SMR with typical reactants such as bromobenzene, phenylboronic acid and the base of K₃PO₄.3H₂O at 30 °C in a solvent mixture of water and ethanol (V_H2O : V_ethanol = 3 : 2).