Preparation and application of SBA-15-supported palladium catalyst for Suzuki reaction in supercritical carbon dioxide

Abstract

The external and internal surfaces of SBA-15 were modified by (MeO)₃SiPh and a phosphine ligand, (MeO)₃SiCH₂CH₂CH₂SCH₂C₆H₄PPh₂, before and after the template Pluronic P123 copolymer was removed, respectively. Palladium was then tethered within the cavity of the mesoporous material Ph-SBA-15-PPh₃via a ligand-exchange reaction to provide a new supported palladium catalyst Ph-SBA-15-PPh₃-Pd. This catalyst was demonstrated to be a robust and active catalyst in Suzuki reaction of a wide range of aryl bromides with arylboronic acids in supercritical carbon dioxide. After the reaction mixtures were treated at 90 °C for 24 h, the crude coupling products were obtained as crystalline solids when the reaction temperature was lowered to room temperature and the carbon dioxide was then slowly released. The pure products can be obtained by simple recrystallization in good to excellent yields. The Ph-SBA-15-PPh₃-Pd catalyst has low leaching loss and can be reused at least 7 times without loss of activity.