The Design of Redox-Active, Olefin Polymerization Catalysts Using Late-Transition Metals

Polyolefins are the most widely produced and utilized polymers in the world. To overcome many of the obstacles associated with homogeneous, single-site catalysts, we have chosen to incorporate redox-active functionality into various ligand scaffolds. These ligand frameworks may facilitate the fine-tuning of the electronic environment around the metal center. Currently we have synthesized two new redox-active α [alpha] diimine ligands and are coordinating them with palladium-based metal precursors to give olefin polymerization catalysts. Each ligand was designed to include a different ferrocene moiety that has the ability to participate in redox chemistry. The redox capabilities of each catalyst will be examined to see if their activities can be fine-tuned in order to produce new polyolefins with new and/or enhanced mechanical properties. In addition to the α [alpha] diimine ligands, attempts to synthesize redox-active phenoxyimine ligands and one phenoxyketimine ligand, each including a different ferrocene moiety, has thus far proved elusive leading to complex product mixtures though. Currently, reaction conditions are being explored in order to isolate pure products. To compliment the ferrocenyl containing ligands above, acenaphthenequinone-based Brookhart-type ligands were also synthesized and coordinated with PdClMe(COD) [Chloromethyl(1,5-cyclooctadiene)palladium(II)] and NiBr₂(DME) [Nickel(II) bromide, dimethoxyethane adduct] to give previously reported olefin polymerization complexes. The redox potential of those complexes were explored using cyclic voltammetry and cobaltacene was chosen as a suitable chemical reductant. The kinetics of 1-hexene polymerization was examined using the oxidized and reduced catalysts, each of which demonstrated a different polymerization rate. In this case, the polymerization rate of the oxidized catalyst proved to be far more active than the reduced catalyst, a phenomena that we are currently investigating.