Diphosphines with expandable bite angles: highly active ethylene dimerisation catalysts based on upper rim, distally...

Area of Science:

• Organometallic Chemistry
• Catalysis
• Supramolecular Chemistry

Background:

• Calix[4]arenes are versatile platforms for designing complex molecular architectures.
• Diphosphine ligands play a crucial role in coordination chemistry and homogeneous catalysis.
• Nickel complexes are widely studied for olefin oligomerization reactions.

Purpose of the Study:

• To synthesize and characterize novel calixarene-based diphosphine ligands.
• To investigate the coordination behavior of these ligands with Ni(II) ions.
• To evaluate the catalytic performance of the resulting nickel complexes in ethylene oligomerization.

Main Methods:

• Synthesis of cone-5,17-dibromo-11,23-bis(diphenylphosphino)-25,26,27,28-tetrapropoxycalix[4]arene (1) and cone-5,17-bis(diphenylphosphino)-25,26,27,28-tetrapropoxycalix[4]arene (2).
• X-ray crystallography for structural determination of a Ni(II) complex.
• Variable-temperature 1H and 31P NMR spectroscopy to study complex dynamics.
• Ethylene oligomerization reactions using methylaluminoxane (MAO) as a co-catalyst.

Main Results:

• Quantitative formation of Ni(II) chelate complexes with both ligands was observed.
• X-ray structure revealed a unique Ni atom positioning and C(1) symmetry.
• Variable-temperature NMR studies identified distinct dynamic motions of the complexes.
• The nickel complexes, activated by MAO, demonstrated high activity in ethylene dimerization, producing 1-butene selectively.

Conclusions:

• The preorganized calixarene diphosphine ligands form stable chelates with Ni(II).
• The dynamic behavior of the nickel complexes influences their catalytic properties.
• These systems represent highly active and selective catalysts for ethylene dimerization, with potential for controlled 1-butene production.