Synthesis of and ethylene oligomerization with binuclear palladium catalysts having sterically modulated bis-imine ligands with methylene spacer

Sterically modulated bis-imine ligands (L¹-L³) were prepared by reacting 4,4′-methylene bis-(2,6-dialkyl aniline) and antipyrine-4-carboxaldehyde in a 1:2 stoichiometric ratio. The reactions of L¹-L³ with dichloro(cycloocta-1.5-diene)palladium(II) PdCl₂(cod)] yield the corresponding binuclear palladium complexes with the general formula Pd₂Cl₄L (L = L¹, L², and L³). The binucleating ligands bind to the palladium ion via the lone pair on the imine nitrogen and amide oxygen atoms, resulting in a square-planar geometry around the metal center. All the palladium catalysts efficiently oligomerize ethylene to produce C₄-C₂₀ fractions at activities of up to 1308 kg-oligomer mol-Pd⁻¹ bar⁻¹ h⁻¹ at 30 °C in combination with ethylaluminum sesquichloride. The formation of active sites by the change in geometry of the metal complexes could be traced using spectroscopic and electrochemical techniques.