Cis-Chelating Diphosphanes for Intracavity Nickel(II)-Catalyzed Ethylene Oligomerization

Area of Science:

• Supramolecular Chemistry
• Organometallic Chemistry
• Catalysis

Background:

• Cyclodextrins (CDs) are versatile hosts for encapsulating guest molecules.
• Metal complexes confined within supramolecular hosts offer unique catalytic properties.
• Ethylene oligomerization is a key industrial process for producing linear alpha-olefins.

Purpose of the Study:

• To synthesize and characterize novel cyclodextrin-derived diphosphine ligands.
• To investigate the catalytic activity and selectivity of Ni(II) and Pd(II) complexes with these ligands in ethylene oligomerization.
• To elucidate the role of the cyclodextrin cavity in influencing catalytic performance.

Main Methods:

• Synthesis of four cis-chelating diphosphanes based on cyclodextrins.
• Complexation of Ni(II) or Pd(II) metal centers within the cyclodextrin cavities.
• Ethylene oligomerization reactions using modified methylaluminoxane (MMAO) as activator.
• Analysis of catalytic activity and product selectivity (GC analysis).
• Computational studies (DFT) to understand reaction mechanisms.

Main Results:

• Nickel(II) complexes of CD-diphosphanes effectively catalyze ethylene oligomerization.
• Product selectivity is influenced by the cyclodextrin cavity size and ligand structure.
• 1-Butene is the predominant product, achieving up to 90% selectivity within C4 fractions.
• Catalyst activity is modulated by the P2Ni fragment's position relative to the cavity.

Conclusions:

• CD-encapsulated metal complexes provide a powerful platform for selective olefin oligomerization.
• The confined supramolecular environment restricts olefin isomerization, favoring alpha-olefin formation.
• These findings open avenues for designing advanced catalysts with tailored selectivity.