Nickel-beta-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 beta-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 210,000h(-1)). The best selectivities were obtained with the heterogenized catalysts, which give 100% of C-4 fraction with 1-butene selectivities of up to 91%. (C) 2012 Elsevier B.V. All rights reserved.