(Pyrazolyl)-(phosphinoyl)pyridine iron(II), cobalt(II) and nickel(II) complexes: Synthesis, characterization and ethylene oligomerization studies

• Ni, Co and Fe complexes were evaluated as ethylene oligomerization catalysts.
• Pre-catalysts activated with EtAlCl2, MAO and AlMe3 co-catalysts.
• Activity and selectivity were co-catalyst, solvent and complex structure dependent.
• Selectivity of oligomer products was mainly towards 1-butene.

New (pyrazolyl)-(phosphinoyl)pyridine ligands 2-((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-6-((diphenylphosphinoyl)methyl)pyridine (L1b) and 2-((3,5-diphenyl-1H-pyrazol-1-yl)methyl)-6-((diphenylphosphinoyl)methyl)pyridine (L2b) were synthesized in high yields. Reactions of L1b and L2b with Fe(II), Co(II) and Ni(II) salts afforded complexes [NiCl2(L1b)] (1), [NiBr2(L1b)] (2), [CoCl2(L1b)] (3), [FeCl2(L1b)] (4), [NiBr2(L2b)] (5), and [CoCl2(L2b)] (6) in good yields. The compounds were characterized by NMR spectroscopy, mass spectrometry and elemental analyses. Molecular structures of complexes 1, 5 and 6 were confirmed by single crystal X-ray crystallography to contain one tridentate bound NˆNˆO L1b and L2b ligands. Complexes 1–6 formed active catalysts in ethylene oligomerization reactions upon activation with EtAlCl2, methylaluminoxane (MAO) or trimethylaluminium (AlMe3) as co-catalyst to produce C4 as the major product as well as C6 and C8 oligomers. The nature of solvent and co-catalyst, significantly affected both the activities and product compositions of the resultant catalysts.

Activation of (pyrazolyl)-(phosphinoyl)pyridine iron(II), cobalt(II) and nickel(II) with MAO in toluene solvent resulted in the formation of active catalysts to afford C4, C6 and C8 while activation of these complexes with EtAlCl2 in either hexane or chlorobenzene solvents produced mainly C4 and C6 oligomers.Figure optionsDownload as PowerPoint slide