Highly active self-assembled group-IV-metal multinuclear catalysts for ethylene polymerization

•Highly active multinuclear Group-IV-metal catalysts were developed.•Multinuclear catalysts were prepared by three linking strategies.•Multinuclear catalysts displayed higher activity and better thermal stability.•Polyethylene with higher MW was produced using multinuclear catalysts.•Multinuclear catalyst with shorter spacer displayed better propylene incorporation.

Group-IV metals play an important role in the production of practical catalysts for polyethylene industry. To develop new highly active catalysts, we designed a new self-assembly strategy that leads to a new family of group-IV-metal multinuclear catalysts with bis-phenoxy-imine ligands. These multinuclear catalysts are formed via three bridging strategies, by linking the imine-N, the 4-position of phenolate, or the mixed linking strategy. The coordination environment of the catalysts was investigated with far-IR and Raman. The multiple imine-H shift found in 1H NMR revealed that the multinuclear catalysts are typical multi-site catalysts comprising of different coordination geometries. All the multinuclear catalysts were more active and stable, and produced polyethylene of higher MW than the corresponding mono-nuclear catalysts. The bridging spacer has an evident effect on catalytic activity, stability, polymer MW and incorporation rate of propylene into the polyethylene backbone.

Graphical abstractA new family of multinuclear catalysts was developed by self-assemble of group-IV metals with bis-phenoxy-imine ligands via three linking strategies. All the new multinuclear catalysts displayed higher activity and better stability compared to corresponding mono-nuclear catalysts.Figure optionsDownload full-size imageDownload as PowerPoint slide