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

The immobilization of a Pd complex on several supports was attempted using a simple method. For this purpose, bis(triphenylphosphine)palladium(II) dichloride(Pd(PPh3)2Cl2) was attached to several oxides including MgO, γ-Al2O3, TiO2, and zeolites. Pd(PPh3)2Cl2 supported on zeolite β remained mostly intact, whereas the complex completely decomposed to provide metal Pd or PdO on MgO and γ-Al2O3, as analyzed by Pd K-edge X-ray absorption fine structure spectroscopy (XAFS). The specific surface area was slightly reduced after Pd(PPh3)2Cl2 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 (PPh3), it was supposed that the PPh3 ligand of Pd(PPh3)2Cl2 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(PPh3)2Cl2. 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).