Alkali-exchanged sepiolites containing palladium as bifunctional (basic sites and noble metal) catalysts for the Heck and Suzuki reactions Original Research Article

Alkali-exchanged sepiolites-containing PdCl2 act as bifunctional heterogeneous catalysts for the Heck and Suzuki cross-coupling in the absence of extrinsic base. The catalyst becomes deactivated upon reuse and partial reactivation can be achieved by mild steaming at 150 °C. Sodium sepiolites were found the most suitable support of the series. Surprisingly, natural sepiolite exhibiting very weak basicity being not able to catalyse the Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate is an adequate basic support for PdCl2. Titration shows that natural sepiolite contains 0.065 equivalents of basic sites/100 g against strong acids. Upon deactivation of natural sepiolite, no measurable reactivation for the solid could be achieved. We suggest that natural sepiolite undergoes an irreversible depletion of the basic sites during the course of the Heck or Suzuki reactions.