Direct immobilization of triphenylphosphine palladium complexes on the external surface of zeolite β

Abstract

Abstract The immobilization of a Pd complex on several supports was attempted using a simple method. For this purpose, bis(triphenylphosphine)palladium(II) dichloride(Pd(PPh 3 ) 2 Cl 2 ) was attached to several oxides including MgO,γ-Al 2 O 3 , TiO 2 , and zeolites. Pd(PPh 3 ) 2 Cl 2 supported on zeolite β remained mostly intact, whereas the complex completely decomposed to provide metal Pd or PdO on MgO and γ-Al 2 O 3 , as analyzed by Pd K-edge X-ray absorption fine structure spectroscopy (XAFS). The specific surface area was slightly reduced after Pd(PPh 3 ) 2 Cl 2 loading on zeolite β, probably due to the deposition of the complex on the external surface. From a comparison experiment using the adsorption of triphenylphosphine (PPh 3 ), it was supposed that the PPh 3 ligand of Pd(PPh 3 ) 2 Cl 2 was inserted into the pores of zeolite β located close to the external surface. The Pd complexes immobilized on zeolite β exhibited much higher activity for allylic alkylation compared with that of pristine Pd(PPh 3 ) 2 Cl 2 . Recycling of the zeolite β loaded Pd complex was possible after the used catalyst was rinsed with toluene. The activity of the Pd complex loaded on zeolite β was enhanced by the addition of a small amount of leucomalachite green (LMG) or leucocrystal violet (LCV).