Mono(phenoxy-imine) Group 4 Trialkyl Complexes: A Family of Olefin Polymerization Catalysts

Organometallic catalysis relies on the proper pairing of ligands with metal precursors, and the traditional method of developing molecular catalysts mainly focuses on ligand engineering. However, the exploration of metal precursors is largely underdeveloped. Here, we report a bulky metal precursor strategy to unlock new catalysts. The reaction of phenoxy-imine (FI) ligand with M(CH2SiMe3)4 (M = Ti, Zr, Hf) produced a family of mono-FI group 4 trialkyl complexes, which featured easy synthesis, diverse structures, high yields, and low cost. These complexes are efficient single-site ethylene (co)polymerization catalysts, as their activities are comparable to those of commercially relevant catalysts under identical polymerization conditions. Notably, the highly tunable nature of the ligands allows for the control of molar mass and comonomer incorporation over a wide range, rendering them good candidates for diverse applications. With the new method, previously challenging-to-obtain binuclear olefin polymerization catalysts were also easily synthesized. They showed superior performance compared to their mononuclear analogues, with an unprecedented significant increase in both molar mass and 1-octene enchainment observed at high activities. Specifically, binuclear catalyst containing both rigid and flexible fragments showed >30% 1-octene incorporation, which is higher than any of the mononuclear analogues. Such strong binuclear effects may be partially due to the metal–metal cooperative effect.