Benchtop-Stable Carbyl Iminopyridyl Ni^II Complexes for Olefin Polymerization

Area of Science:

• Catalysis
• Polymer Chemistry
• Organometallic Chemistry

Background:

• Traditional Ni-catalyzed olefin polymerization relies heavily on ligand design for controlling polyolefin structures.
• The activation process of Ni(II) precatalysts often involves in situ alkylation, which can be complex and limit catalyst scope.

Purpose of the Study:

• To develop air-stable Ni(II) precatalysts activated solely by halide abstraction.
• To investigate the role of cocatalyst-derived ion pairs in olefin polymerization.
• To achieve broader control over polyolefin molecular weights and microstructures by manipulating the activation process.

Main Methods:

• Design and synthesis of air-stable alkyl- or aryl-functionalized Ni(II) precatalysts.
• Activation of precatalysts using organoboron and organoaluminum cocatalysts.
• Polymerization studies under high ethylene pressure.
• Density Functional Theory (DFT) calculations to elucidate reaction mechanisms.

Main Results:

• Precatalysts activated by halide abstraction yielded higher molecular weight homo/copolymers compared to traditional methods.
• Organoboron cocatalysts formed well-defined ion pairs, leading to more controlled polymerization than organoaluminum cocatalysts.
• High ethylene pressure enabled broader branching densities and gradual short-chain branch incorporation.
• A phenyl group on the bridging carbon increased polymer molecular weight compared to methyl-substituted analogs.

Conclusions:

• Air-stable Ni(II) precatalysts activated by halide abstraction offer a new route to polyolefin synthesis.
• Ion pair interactions are crucial for controlling polymerization outcomes, with well-defined ion pairs promoting higher molecular weights.
• This approach provides a versatile platform for tuning polyolefin micro- and macrostructures, reducing reliance on intricate ligand design.