Enhancing catalytic activity towards Heck-reaction by using 4,5,9,10-tetra(arylimino)pyrenylidenyldipalladium tetrachlorides

Abstract

A series of binuclear 4,5,9,10-tetra(arylimino)pyrenylidenyldipalladium(II) tetrachloride complexes (Pd1–Pd4) was synthesized and characterized by FT-IR and NMR spectroscopy as well as elemental analysis. The molecular structures of representative complexes Pd1 and Pd2 were determined by single crystal X-ray diffraction to reveal a square planar geometry around the palladium centre. The complex Pd1 dissolved in the presence of ethanol to form mono-palladium complex C1, whose structure was also confirmed by single crystal X-ray diffraction. All binuclear palladium complexes promote the Heck cross-coupling reactions with high activities; the reaction can be carried out for various substrates and activators (basic compounds) and also in various solvents. The binuclear palladium complexes exhibit significantly higher efficiency than do their mono-palladium complexes bearing 4,5-bis(arylimino)pyrenylidenes.