Bulky o-Phenylene-Bridged Bimetallic α-Diimine Ni(II) and Pd(II) Catalysts in Ethylene (Co)polymerization

The bimetallic synergistic strategy has attracted interest and been frequently explored in late-transition-metal-catalyzed olefin (co)polymerization. In this contribution, a series of bulky o-phenylene-bridged bimetallic α-diimine Ni(II) and Pd(II) catalysts were designed, synthesized, and investigated in ethylene polymerization and copolymerization with polar monomers. The molecular structures of bimetallic Pd(II) complexes have been determined by X-ray diffraction. The bimetallic Ni(II) catalysts exhibit excellent activity and generate high-molecular-weight polyethylene with lower branching density in comparison with the corresponding monometallic analogues. Moreover, the mechanical properties of the obtained polyethylene products could be adjusted in a wide range by the structures of the Ni(II) catalysts and the polymerization conditions. In particular, polyethylene materials generated by Ni2-Me and Ni2-iPr exhibited excellent mechanical properties and up to 86% strain recovery value (SR), comparable to the best reported recovery values of polyethylene thermoplastic elastomers. Furthermore, bimetallic α-diimine Pd(II) catalysts are more efficient than the corresponding monometallic analogues in terms of polymerization activity, molecular weight, and branching density. In addition, these bimetallic Pd(II) complexes are also tolerant of polar monomers in copolymerizations with ethylene.