Pd Catalyst Based on Hyperbranched Polypyridylphenylene Formed In Situ on Magnetic Silica Allows for Excellent Performance in Suzuki-Miyaura Reaction.

Here, for the first time, we developed a catalytic composite by forming a thin layer of a crosslinked hyperbranched pyridylphenylene polymer (PPP) on the surface of mesoporous magnetic silica (Fe3O4-SiO2, MS) followed by complexation with Pd species. The interaction of Pd acetate (PdAc) with pyridine units of the polymer results in the formation of Pd2+ complexes which are evenly distributed through the PPP layer. The MS-PPP-PdAc catalyst was tested in the Suzuki-Miyaura cross-coupling reaction with four different para-Br-substituted arenes, demonstrating enhanced catalytic properties for substrates containing electron withdrawing groups, and especially, for 4-bromobenzaldehyde. In this case, 100% selectivity and conversion were achieved with TOF of >23,000 h-1 at a very low Pd loading (0.032 mol%), a remarkable performance in this reaction. We believe these exceptional catalytic properties are due to the hyperbranched polymer architecture, which allows excellent stabilization of catalytic species as well as a favorable space for reacting molecules. Additionally, the magnetic character of the support allows for easy magnetic separation during the catalyst synthesis, purification and reuse, resulting in energy and materials savings. These factors and excellent reusability of MS-PPP-PdAc in five consecutive uses make this catalyst promising for a variety of catalytic reactions.