Pd-catalyzed ethylene/methyl acrylate cooligomerization: the effect of a new nonsymmetric alfa-diimine with the 1,4-diazabutadiene skeleton

Palladium(II) complexes with a nonsymmetric bis(aryl-imino)diazabutadiene ligand (ArDAB) have been synthesized and characterized. The new ligand is featured by one aryl ring substituted in ortho positions with methyl groups and the other ring bearing a trifluoromethyl group on the meta positions, leading to a subtle steric and electronic difference on the two nitrogen-donor atoms. This peculiar substitution makes the direct synthesis of the ligand not feasible, and the relevant Pd(II) complex, [Pd(CH3)Cl(ArDAB)], is directly obtained through a template reaction. The corresponding cationic complexes with either acetonitrile or dimethyl sulfoxide have been synthesized and characterized. The X-ray crystal structure of a palladium complex with an -diimine and dimethyl sulfoxide is reported. The monocationic complexes have been tested as precatalysts in the ethylene/methyl acrylate cooligomerization under mild reaction conditions of temperature and pressure. The comparison with the catalytic behavior of the precatalysts with the corresponding nonsymmetric ArBIAN ligand indicated that the active species with the currently investigated ligand is more productive, leading to the formation of ethylene oligomers and ethylene/methyl acrylate cooligomers.