Novel ordered cyclopalladated aryl imine monolayers—Structure Designing for Enhancing Catalytic Performance

Abstract

Two new Schiff-based cyclopalladated aryl imine catalysts (denoted as Fc-Pd and B-Pd) were prepared and their ordered self-assembled molecular monolayers (called as Si@F-Pd and Si@B-Pd) were fabricated. Their catalytic performances were evaluated using Suzuki coupling reaction as a templet with water as solvent, in which the structure on their catalytic properties and mechanism were systematic studied. Si@F-Pd and Si@B-Pd exhibited higher catalytic active with higher turnover number (TON) (149095 and 173214) and could be recycled at least 8 time and 6 time, respectively. The molecular structure and geometry of the catalyst was an important factor for their catalytic performance and stability, in which that large steric and structure made it easy to alter the electronic environment and structure, regulate the state of catalytic active surface which are contributed to their high catalytic activity. It was the fact that the electron rich of Pd may be formed by transferring electrons from ligand to Pd which became more nucleophilic for enhancing the facile oxidative addition with aryl halides. The catalytic mechanism proceeded a quasi-homogenous property on the surface in the form of leaching and re-deposition manner. Si@Fc-Pd acted as catalytic sites (surface) and sources or likely a reservoir for active species leaching, which formed a cycling state of equilibrium. It was clarified that the homogeneous and heterogeneous catalysis occurred at the same period on the surface and in solution, which was confirmed by hot-filtration, poison text, three-phase text, AFM, CV, XPS and ReactIR.