Design and Synthesis of Late Transition Metal Complexes for Ethylene (co)Polymerizations
- Author(s): Crumrine, Justin Daniel
- Advisor(s): Guan, Zhibin
- et al.
Polyolefins comprise the largest group of commercially produced polymers worldwide, finding extensive uses as plastics, textiles, and elastomers. These polymers are produced by insertion polymerization, catalyzed by various transition metals, from the abundant gaseous fossil feedstocks, ethylene and propylene. Although there have been monumental achievements in designing suitable transition metal catalysts, both academically and industrially, the efficient copolymerization of ethylene or propylene with polar functional olefins remains a major challenge for the polymer science field. A scant few catalysts have been discovered that can perform this copolymerization and these were based on late transition metals due to their tolerance of polar functionality. This thesis presents work aimed at the development of late transition metal polymerization catalysts based on cobalt, palladium, and ruthenium.
A series of complexes based on Co(II) were designed, synthesized, and evaluated for olefin polymerization. Complexes of the general type CoCl(O,N,N) featuring novel anionic ligands with oxygen and nitrogen donor atoms (O,N,N = steric and electronic variants of phenolate-pyridine-imine ligands), were found to be active ethylene polymerization and oligomerization catalysts. A positive correlation with the ligand’s steric bulk and both polymerization and oligomerization activity was observed. These catalysts were inactive for copolymerization of ethylene with polar comonomers.
Another approach to solve this problem was based on Pd(α-diimine) complexes that contained tethered olefins or boronic ester groups. Pd(α-diimine) complexes are known to be able to copolymerize ethylene with polar acrylate comonomers. It was hypothesized that the pendant, Lewis acidic, boronic ester group could influence incorporation ratios through interactions with the Lewis basic oxygen atom of the acrylate monomer. However, no effect was observed for the boronic ester modified complex. The tethered olefin containing complexes were observed to have longer catalyst lifetimes, at the expense of activity, due to the hemilabile ability of the olefin to coordinate to the active Pd species.
Other investigations included the synthesis of various complexes based on ruthenium employing N-heterocyclic carbene and pyridine based ligands. These complexes displayed very low or no activity in catalyzing the polymerization of ethylene, and were inactivated by the addition of polar monomers.