Palladium-Catalyzed Ethylene/Methyl Acrylate Co-Oligomerization: The Effect of a New Nonsymmetrical -Diimine with the 1,4-Diazabutadiene Skeleton

Pd-II complexes with a nonsymmetrical bis(aryl-imino)diazabutadiene ligand (ArDAB) have been synthesized and characterized. The new ligand features one aryl ring substituted in the ortho positions with a methyl group and the other ring that bears a trifluoromethyl group on the meta positions, which leads to subtle steric and electronic differences at the two N donor atoms. This peculiar substitution makes the direct synthesis of the ligand unfeasible, and the relevant Pd-II complex, [Pd(CH3)Cl(ArDAB)], is obtained directly through a template reaction. The corresponding cationic complexes with either acetonitrile or DMSO were synthesized and characterized. The X-ray crystal structure of a Pd complex with an -diimine and DMSO is reported. The monocationic complexes were tested as precatalysts in ethylene/methyl acrylate co-oligomerization under mild reaction temperature and pressure conditions. A comparison of the catalytic behavior of the precatalysts with the corresponding nonsymmetrical aryl -diimines with an acenaphthene skeleton indicated that the active species with the new ligand is more productive and leads to the formation of ethylene oligomers and ethylene/methyl acrylate co-oligomers.