Ethylene Polymerization by Xanthene‐Bridged Dinuclear α‐Diimine NiII Complexes

The synthesis, characterization, and ethylene polymerization properties of a series of xanthene‐bridged dinuclear α‐diimine NiII complexes are described. The dinucleating α‐diimine ligands were prepared from the xanthene‐bridged di‐anilines, which were synthesized and isolated on the multigram scale without using column chromatography. The di‐anilines could potentially be used to prepare various dinucleating imine‐containing olefin polymerization ligands. In ethylene polymerization, the dinuclear α‐diimine NiII complexes showed good thermal stability and high catalytic activity. In addition, the polyethylene generated by these dinuclear α‐diimine NiII complexes showed high molecular weight, narrow polydispersity, and very low branching density. Metal–metal cooperativity effects was invoked to explain the slow β‐hydride elimination process and the correspondingly slow chain‐walking process.