A simple, recyclable, and self-assembled palladium(ii)–alkyl Schiff base complex for Suzuki coupling reaction: chain length dependence and heterogeneous catalysis

Abstract

A series of self-assembled Pd(II)–alkyl Schiff base complexes [PdL_n–Si] (Cat. 1–5) [n = 0, 1, 3, 6, 10] having different chain lengths were synthesized and characterized by water drop contact angle (WDCA), atomic force microscopy (AFM), ultraviolet-visible spectroscopy (UV-Vis), Raman spectroscopy (RS), and X-ray photoelectron spectroscopy (XPS) analyses. Catalyst 3 with a moderate alkyl chain exhibited highly active and recyclable properties for the Suzuki coupling reaction, which indicated that the length of the alkyl chain significantly affects the catalytic activity due to a suitable orientation and electron-rich environment which make it easy to form palladium–ligand bonds, stabilize the active species and facilitate the insertion of this metal into the Ar–X bond. The catalytic mechanism was also investigated, in which a three-phase test indicated that the self-assembled complexes act as true heterogeneous catalysts. The catalytic process was analyzed by RS and XPS, indicating it is a surface catalysis process.