Phosphine-sulfonate-based nickel catalysts: ethylene polymerization and copolymerization with polar-functionalized norbornenes

In this contribution, the effect of substitution on biaryl-based phosphine-sulfonate nickel catalysts is investigated. A series of [κ2-(P,O)-2-(P-PhAr)-1-benzenesulfonato]NiPh(PPh3) nickel complexes (Ni–OMe, Ar = 2-[2′,6′-(OMe)2-C6H3]-C6H4; Ni–H, Ar = 2-(C6H5)-C6H4; Ni–OiPr, Ar = 2-[2′,6′-(OiPr)2-C6H3]-C6H4; Ni–F, Ar = 2-[2′,6′-F2-C6H3]-C6H4) are prepared and applied to the polymerization of ethylene as well as its copolymerizations with polar functionalized norbornene comonomers. These nickel complexes are highly active toward ethylene polymerization without the requirement of any cocatalyst. Specifically, the Ni–F complex exhibits high stability and high activity (up to 3.0 × 106 g mol−1 h−1), and catalyzes the formation of polyethylene of high molecular weight (Mn up to 216 200) and high melting point (Tm up to 139.6 °C). The polyethylene molecular-weight distribution from this system is very sensitive to the steric demand of the ligand, as well as the nature of the coordinating base, polymerization temperature, and ethylene pressure. This, in turn, provides a simple and efficient strategy for the control of the polyethylene molecular-weight distribution, which is an important parameter that determines multiple material properties such as viscosity, stiffness, and crystallinity. Ni–F also exhibits good ethylene-copolymerization behavior toward polar-functionalized norbornene comonomers, leading to moderate comonomer incorporation in copolymers of moderate molecular weight and high melting point.