Nickel and palladium complexes bearing ortho-phenoxy modified anilido-imine ligands: Drastic steric effect on coordinated geometry, and catalytic property toward olefin polymerization

A series of new nickel complexes and palladium complexes bearing ortho-phenoxy modified anilido-imine ligands have been synthesized and characterized. X-ray diffraction analyses of the single crystal structures reveal that there are no direct metal-O interactions in all of the complexes. The steric hindrance of complexes has an importance influence on their coordinated geometries. The bulky complexes with 2,6-diisopropylphenyl substituent exist as a dimers with bromine-bridged structure while those with 2,6-dimethylphenyl or phenyl substituents adopt a distorted tetrahedral geometry with four nitrogen atoms of two anilido-imine ligands. The nickel complexes exhibited high activity up to 7.33 × 10⁶ g/(mol of Ni · h) and palladium complexes showed very high activity up to 2.63 × 10⁸ g/(mol of Pd · h) for norbornene polymerization with methylaluminoxane as cocatalyst. The nickel catalysts were attempted to polymerize ethylene at atmosphere pressure, however, only oligomers were produced.