The phosphine phosphonic amide ligand platform is highly versatile, with three positions that can be independently tuned. In this contribution, we wish to study the nickel complexes based on this ligand system. Interestingly, the nickel dibromide and nickel allyl complexes are not active in ethylene polymerization. In contrast, the nickel phenyl chloride complexes are highly active in ethylene polymerization in the presence of a sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate cocatalyst. In addition, these nickel complexes can initiate ethylene copolymerizations with polar functionalized comonomers including methyl 10-undecenoate, 6-chloro-1-hexene and 5-acetoxy-1-pentene. More interestingly, these nickel complexes can oligomerize 1-hexene and 6-chloro-1-hexene.

Two phosphine–sulfonate ligands, bearing both the ferrocene and the bi‐aryl units, were prepared and characterized. The corresponding palladium and nickel complexes are active in ethylene polymerization. In both the palladium and the nickel systems, the oxidation of the ferrocene unit leads to a decrease in catalytic activities and the polymer molecular masses. Interestingly, the neutral palladium catalyst is not active for norbornene polymerization, while the oxidized analogue shows good activity. As such, switchable polymerization could be achieved.

Heterogeneous catalysts have been dominant for industrial polyolefin production, offering many distinct advantages, such as controlling the morphology of the polymer and preventing reactor fouling. In this contribution, we designed several types of imine ligands bearing sodium-sulfonate ionic groups and the corresponding nickel/iron catalysts. These catalysts could be immobilized on SiO 2 with strong affinity and high catalyst loadings. The SiO 2 -supported catalysts behaved better than their homogeneous counterparts during ethylene polymerization with extremely high activity (2.6 × 10 4 kg• mol) and high thermal stability. In addition, the supported nickel catalysts generated free-flowing polyethylene with high molecular weight (M n up to 2.65 × 10 3 kg• mol -1) and excellent morphology control, indicating no reactor fouling due to the leaching of catalyst. Moreover, for copolymerization, immobilized nickel catalysts showed a higher tolerance of polar monomers, and the efficient copolymerization of ethylene with undecylenic acid was achieved with high activity (450 kg• mol) and a high incorporation ratio (up to 12.3%).

No abstract

The synthesis of ultrahigh molecular weight polyethylene (UHMWPE) using late transition metal catalysts is highly challenging. In this work, 3,5-bis­(trifluoromethyl)­phenyl and m-xylyl groups were selected to introduce at the ortho position of 4-(trifluoromethyl)­aniline and 4-methylaniline. These amines were condensed with 2,3-butandione and 3-substituted salicylaldehyde and subsequently with nickel precursors to afford cationic keto-imine-based Ni1 and Ni2, as well as 3-substituted neutral phenoxyiminato Ni3 and Ni4 catalysts. The properties of these nickel complexes in ethylene polymerization and copolymerization were studied in detail. Ni2 with a keto-imine framework was found to be highly active in ethylene polymerization with an activity of up to 6.9 × 106 g·mol–1·h–1, whereas the fluorinated Ni1 generated UHMWPE with M n of up to 2.79 × 106 g·mol–1, along with very low branch density and high T m values. These nickel catalysts also showed good activity and incorporation of long-chain special polar monomers. It is believed that the higher steric hindrance of fluorine atoms around the metal center may involve suppressing the chain transfer process.