A highly crosslinked, mesoporous poly(ionic liquid) containing salen–Pd for efficient, eco-friendly Suzuki–Miyaura coupling reactions

Abstract

Pd-catalyzed Suzuki–Miyaura cross-coupling reactions have attracted considerable attention. Porous organic polymers (POPs) are potential heterogeneous catalysts to overcome the shortcomings of the homogeneous reaction. However, most POPs are microporous, which strongly hindered the mass transfer process during the catalytic reaction. In this work, a Pd-containing, highly crosslinked, mesoporous poly(ionic liquid) (SMPIL–Pd) was designed as a heterogeneous catalyst for efficient Suzuki–Miyaura coupling reactions. This catalyst was fabricated by hyper-crosslinking of a salen-containing mesoporous poly(ionic liquid) via a simple Friedel–Crafts alkylation reaction followed by Pd(II) coordination via the –N₂O₂– tetradentate structure of the salen structure. A series of characterization studies revealed that SMPIL–Pd possesses predominant porosity and extremely rigid networks, highly dispersed catalytic active sites, mesoporous structures, and large specific surface areas. Consequently, this catalyst exhibited excellent catalytic activity towards Suzuki–Miyaura coupling reactions under an air atmosphere in 50% aqueous ethanol. SMPIL–Pd also demonstrated outstanding stability and recyclability, and it can be reused seven cycles without a significant loss of activity.