Ethylene oligomerization using nickel-β-diimine hybrid xerogels produced by the sol–gel process

Nickel-β-diimine complexes have been used as homogeneous- and heterogeneous-phase oligomerization catalysts. The following complexes have also been heterogenized on silica using the sol–gel method: 1,5-bis(phenyl)-pentanediimine-dibromonickel(II) (A), 1,5-bis(2,6-dimethylphenyl)-2,4-pentanediimine-dibromonickel(II) (B) and 1,5-bis(2,4,6-trimethylphenyl)-2,4-pentanediimine-dibromonickel(II) (C). The synthesis of the xerogels was performed employing 3-chloropropyltrimethoxysilane (CPTMS), tetraethylorthosilicate (TEOS) and HF. The hybrid β-diimine/silica materials are used in combination with ethylaluminum sesquichloride (EASC) and have been shown to be outstanding ethylene oligomerization catalyst systems. Under mild reactions conditions, the homogeneous and heterogenized catalysts had high turnover frequencies (between 1800 and 210,000 h−1). The best selectivities were obtained with the heterogenized catalysts, which give 100% of C4 fraction with 1-butene selectivities of up to 91%.

Hybrid silica was synthesized by the sol–gel method and subsequently complexed with metal to form a heterogenized nickel-β-diimine/silica complex, which was employed in ethylene-oligomerization reactions.Figure optionsDownload high-quality image (146 K)Download as PowerPoint slideHighlights
► Three β-diimine ligands and their corresponding nickel-complexes were synthesized.
► Hybrid silica containing β-diimine groups were prepared by sol–gel process.
► Hybrid silica were complexed with nickel to form heterogenized nickel-complex.
► Ethylene oligomerization using nickel-β-diimines was described.
► Ligands nature were correlated with the catalytic activity and selectivity.