A series of ligands and cobalt complexes were synthesized and characterized using NMR spectroscopy, elemental analysis and single-crystal X-ray diffrac-features a monomeric structure with κ 2 coordination of the silicon-bridged diphosphine ligand to the cobalt center.Using dried methylaluminoxane (DMAO) and AlEt 3 as co-catalysts and methylcyclohexane as solvent, the Co(II) complex proved to be moderately active and highly selective for ethylene dimerization. The effects of ligand structure, catalyst loading, reaction temperature, Al/Co molar ratio, DMAO/ AlEt 3 molar ratio and reaction time were investigated with respect to the catalytic activity and product selectivity of ethylene dimerization. Cobalt complex C1 exhibited moderate catalytic activity of 2.3 × 10 5 g (mol Co ) −1 h −1 , with 100% selectivity towards C 4 (87% 1-C 4 in the C 4 fraction).