Deactivation pathways of neutral Ni(II) polymerization catalysts

Area of Science:

• Organometallic Chemistry
• Catalysis Research
• Nickel Complexes

Background:

• Understanding the behavior of neutral Ni(II) catalysts is crucial for developing efficient catalytic processes.
• Direct observation of catalyst activation and deactivation pathways provides fundamental insights into reaction mechanisms.

Purpose of the Study:

• To synthesize and characterize a novel Ni(II) complex as a precursor for studying catalyst activation and deactivation.
• To investigate the reactivity of this precursor with ethylene, including insertion, decomposition, and dimerization reactions.
• To determine the influence of water on the catalytic performance of the Ni(II) system.

Main Methods:

• Synthesis of a novel dimethyl sulfoxide (DMSO)-coordinated nickel(II) complex, [(N,O)Ni(CH(3))(DMSO)] (1-DMSO).
• Reaction of 1-DMSO with ethylene to form the ethyl complex [(N,O)Ni((alpha)CH(2)(beta)CH(3))(DMSO)] (2-DMSO).
• Kinetic studies to determine rate constants and thermodynamic parameters for various reaction pathways, including decomposition and reactions with hydride complexes.

Main Results:

• 1-DMSO was identified as a reactive precursor enabling direct observation of Ni(II) catalyst activation and deactivation.
• Ethylene insertion into the Ni(II)-Me bond formed the ethyl complex (2-DMSO), which could undergo interconversion via a Ni(II)-hydride intermediate.
• Key decomposition pathways were identified, including bimolecular elimination of ethane from the Ni(II)-Me complex and reaction of Ni(II)-Et with Ni(II)-H.
• Hydrolysis by water was found to be a minor decomposition route, with no significant impact on ethylene insertion or dimerization rates.

Conclusions:

• The novel Ni(II) precursor provides a unique platform for mechanistic studies of nickel-catalyzed reactions.
• Understanding catalyst deactivation pathways, such as bimolecular elimination and reactions with hydrides, is essential for catalyst design.
• The observed insensitivity to water suggests robustness of the catalytic system under certain conditions.