The recyclable cyclopalladated ferrocenylimine self-assembly catalytic film and investigation of its role in the mechanism of heterogeneous catalysis

Abstract

An efficient, reusable and stable catalyst nano-sheet film (Si-CDI-Pd) was developed, in which cyclopalladated ferrocenylimines were grafted onto silicon, glass and quartz surfaces by covalent bonds. Water contact angle, ultraviolet-visible spectroscopy (UV-Vis), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), low-angle X-ray diffraction (LAXD) and cyclic voltammetry (CV) were used to characterize the structural and compositional information of the modified surfaces. The immobilized catalyst films were tested for the Suzuki–Miyaura reaction and displayed high activity for the preparation of various biaryls at elevated temperatures in neat water without ligands. It also presented good stability and reusability. It can be reused at least 8 times with little Pd leaching into the crude product. The reasonable and feasible reaction mechanism of the heterogeneous Suzuki–Miyaura reaction based on the results of AFM, XPS, and CV tests of different reaction times were explored in detail, in which a cycle of Pd^II to Pd⁰ and Pd⁰ to Pd^II on the surface was clearly detected and illustrated. In this approach, Pd⁰ on the surface of nano-sheet films as an active surface to catalyze the coupling reaction of aromatic halides and borophenylic acid proceeded via a mechanism of surface-catalyzed process.