Tandem ethylene dimerization and Friedel-Crafts alkylation of toluene catalyzed by homo- and heterogeneous nickel(II) and palladium(II) pre-catalysts

Palladium(II) and nickel(II) complexes (1-4) of the Schiff base ligands, N-(2-pyridinylmethylene)-3-(triethoxysilyl)-1-propanamine (L1) and N-(1-(pyridin-2-yl)ethylidene)-3-(triethoxysilyl)-1-propanamine (L2), have been synthesized and characterized by FT-IR and elemental analysis. The palladium complexes were also characterized by multinuclear NMR studies and the molecular structure of one of palladium complex, 1, was authenticated by X-ray crystallography. Complex 1 and the two nickel complexes, 3 and 4, were evaluated as pre-catalysts for ethylene oligomerization reactions using EtAlCl₂ as co-catalyst. On activation with EtAlCl₂, the complexes form active catalysts which dimerize ethylene to mainly butenes and subsequently, and these butenes undergo Friedel-Crafts alkylation of toluene (the solvent used for the ethylene reactions); leading to the formation of regioisomers of mono-, di- and tri-butyltoluenes. The nickel complexes, 3 and 4, were also immobilized on silica support to give the nickel pre-catalysts m1 and m2, which are also active for ethylene dimerization and subsequent Friedel-Crafts alkylation of toluene.