Electronic effects on the structures and catalytic properties of (pyrazol-1-yl)phenylmethanone palladium(II) complexes

Four new (pyrazol-1-yl)phenylmethanone ligands and their palladium(II) complexes were synthesized and characterized by various analytical techniques. The electronic properties of substituents on the phenyl ring of the ligand have significant effects on the structures as well as the catalytic properties of the complexes toward ethylene oligomerization and the subsequent Friedel-Crafts alkylation of toluene by the ethylene oligomers. Electron-withdrawing groups (ca. Cl and F) of the ligands contributed to the formation of binuclear palladium complexes, whereas electron-donating groups (ca. H and CH₃) resulted in the formation of mononuclear complexes. These complexes on activation with EtAlCl₂ form active catalysts which dimerize ethylene to mainly butenes (C4) and subsequent Friedel-Crafts alkylation of toluene by butenes to regioisomers of butyltoluenes. This is the first example of pyrazolyl palladium(II) compounds that perform this tandem reaction of oligomerization and Friedel-Crafts alkylation.